218 thoughts on “Close Air Support fighter proposal 3”

1. This may sound a bit crazy, but may I dare suggest the Gsh-6-30 instead of the proposed cannon?

   The bulk of the problems occurred because the cannon was mounted below the fuselage.

   See here for an in depth description of issues experienced:
   http://www.quarry.nildram.co.uk/GSh-6-30.htm

   The advantage of gas operated guns over electric guns is that they spin up to maximum much faster. I suspect that with some refinements, the problems associated with this gun could be resolved.

   It’s used these days in the Kasthan-M CIWS (videos and links save Wiki in Russian):

   http://militaryrussia.ru/blog/topic-16.html

   http://en.wikipedia.org/wiki/Kashtan_CIWS

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   1. Thanks. I’ll think about it.

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   2. I think Andrei made this suggestion earlier in the other thread as well.

      Hmm, the other option is to build a CAS aircraft around multiple 30mm revolvers or even a slower rate of fire 35 to 40mm gun.

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   3. Problem is, I can’t find its side drawing, which I need for design work (to get accurate idea of how large aircraft will be).

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      1. Still looking for a drawing but:

         http://russianammo.org/Russian_Ammunition_Page_30mm.html

         “The double-barrel GSh-30 measures 2044x222x195mm and is used in fixed installations and underwing gun-pods and has a barrel length of 1500mm. The GSh-30K is a modified version with 2400mm long barrels and an evaporating-type of barrel cooling and variable rate of fire, it is used in fixed helicopter-borne mounts and measures 2944x222x195mm. ”

         “The six-barrel rotary cannon is mounted on bomber-aircrafts as defensive cannon and has a Vo of only 850m/s.
         It is gas operated and 2040mm long and like the above cannons belt fed. ”

         I think the naval version has a higher muzzle velocity (likely due to longer barrels and bigger rounds).

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      2. Yet another option for a lower calibre weapon would be the Gsh-6-23, which was used in Soviet fighters. But I think at that point, it may be best to go back to higher calibre 30 mm weapons.

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2. I wonder if the Oerlikon 35 mm twin cannon could be modified and used on an aircraft? Denel also made a good twin cannon, although it was for CIWS on naval ships. Muzzle velocity of both guns is about 1150 m/s.

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   1. I’ll take a look at it…

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   2. Rate of fire for Oerlikon is 1100 rpm combined, looks a bit slow for ground attack.

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      1. I guess so. It’s the calibre versus rate of fire trade-off. Perhaps 30mm is the optimal point? Unless someone makes a gas operated rotary gun anyways of higher calibre.

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      2. “Perhaps 30mm is the optimal point?”

         Looks that way.

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   3. Hi Chris. Regarding 35mm revolvers. The 3 book series ‘Flying Guns’ (specifically the Modern Era edition) by Anthony G Williams and Dr Emmanuel Gustin had an interesting take on this on page 180.

      “For ‘tank busting’, the USAF’s 30mm GAU-8/A with its DU ammunition currently has no rival, although its size and weight require an aircraft specifically intended for the role to be designed around it. As tank armour improves, so the 30mm calibre becomes more marginal in its effectiveness. If the development of guns for this purpose were to continue, the Oerlikon KDG 35mm revolver cannon would make an interesting alternative, as it has twice the muzzle energy of the GAU-8/A.”

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      1. Thanks for the suggestion, I’m going to redesign a CAS proposal for the nth time, so I’ll take a look into it.

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   4. A link: http://warfaretech.blogspot.com.au/2014/03/oerlikon-35mm-cannon.html

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3. Cannon Issue:

   Whats wrong with GSh-30-2?
   Its on Su-25 ,not subjected to ITAR Perhaps its longer barrel version GSh-30-2K from Hind could be adapted to your AC and revolver should be easily repairable by in field than fancy GAU-12

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   1. Yeah that’s another cannon definitely worth exploring.

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   2. I’ll think about it.

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4. This is the appropriate blog for anyone who wants to learn about this topic. You realize a great deal its practically hard to argue with you (not too I actually would likely want…HaHa). You definitely place a new spin and rewrite on a topic thats recently been written about for years. Great goods, just fantastic!

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5. http://www.flightglobal.com/news/articles/low-cost-scorpion-fighter-starts-flight-tests-394085/

   http://www.flightglobal.com/blogs/the-dewline/2013/12/scorpions-wind-change/

   Picard: Take a peek at these links; are you sure someone is not stealing your ideas? No gun…

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   1. It isn’t unusual for several people to have similar ideas completely independently… for them to have good ideas is quite bit rarer, but still happens.

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      1. Their plane seems to use more composites than what’s being proposed here. The question is, how easy to maintain would a plane that used composites heavily be?

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      2. That depends on type of composites, but using composites for CAS fighter is a problematic proposal.

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      3. If you look at the article:

         “Textron subsidiary Cessna constructed the all-composite Scorpion airframe using a low-cost technique, but it is ready to enter full-rate production, Tutt says.”

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10. The engine is a bit low, Americans use rough landing strips for A-10s. So it might suck in some dust

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    1. Su-25s engine isn’t higher yet it doesn’t have trouble with all kinds of rough strips
       

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       1. Yeah but the SU-25 is pointed up a little.

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11. If I can add a comment… the A-10 had its engines placed where they are as well as high and separate to mask its infrared signature from the ground as well as to lower the possibilities of disabling both engines with one hit. BUT they did consider the lower engines in one of the alternate designs because it would make repairs and maintenance in rough air fields easier and that advantage was discarded only reluctantly in favor of the higher engine location they have now.

    But the A-10 could have looked just like that SU-25 had some different people prevailed on that issue.

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    1. Lower engines you can work them easier from the ground… those high engines require ladders and elevated platforms.

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    2. Su-25 is actually based on the US A-9 proposal.

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13. Do you see any advantages that gunship style CAS plane like the AC-130, might have over a more conventional plane? Is there any advantage to circling around the target firing high calibre cannon? `Or is the AC-130 just typical USAAF wastefulness and duplication.

    A bit off topic, but it was discussed in the comments of your previous CAS proposal: artillery. I am new reader of your site and have in the last week or so read every article available (great stuff) and I normally agree with everything you say. But not regarding self propelled artillery. I cannot disagree regarding its limitations in terms of cost, maintenance and strategic mobility. These however, are all worthwhile tradeoffs. A competent opponent will have counter-battery radar, meaning that towed artillery which is cumbersome to emplace and remove, and is completely unprotected will take very serious losses. SP guns on the other hand can shoot-and-scoot; enabling them to evade counter-battery fire and absorb blast and shell fragments, where the crews of towed artillery would be slaughtered.

    Complexity is not always better, but neither is simplicity. How long would a Spitfire last against a Eurofighter, and this is not a false comparison as towed artillery is in essence unchanged since WW2.

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    1. “Do you see any advantages that gunship style CAS plane like the AC-130, might have over a more conventional plane?”

       Loiter time, maybe, and ability to take out bunkers and such. But being huge, it will be more vulnerable than the A-10.

       “A competent opponent will have counter-battery radar, meaning that towed artillery which is cumbersome to emplace and remove, and is completely unprotected will take very serious losses.”

       Static artillery is always dug-in, meaning that you need a direct hit to take it out. That being said, it is vulnerable to its crew getting taken out, but on the other hand mobile artillery is more easily discovered and attacked.

       “Complexity is not always better, but neither is simplicity. How long would a Spitfire last against a Eurofighter, and this is not a false comparison as towed artillery is in essence unchanged since WW2.”

       There is an article called “Quality vs quantity” on this blog, take a look at the graphs included – basically, increasing complexity does pay off dividends up to a certain point, but after that point it becomes counterproductive. And weapon that is best in one-on-one comparision may not be best in the war.

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       1. ““Quality vs quantity”” – The classic example is when you are flying an attack mission and the quantity of the opposing aircrafts exceed the quantity of your AA missiles… even if every missile hits its target you will eventually be disarmed and forced to flee.

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    2. Bruno, I just saw your post about towed artillery. Yes, you are correct but at the same time you are also overlooking some important advantages of towed artillery; mostly mobility.

       Towed artillery can be moved by helicopters and smaller aircrafts to remote locations where the enemy has no artillery or locations where there is no enemy artillery. An amphibious landing is an excellent example of its use as well as in mountainous terrain where a firing position can support a number of outposts.

       And for remote locations artillery will provide timelier fire than the alternative which will be aircrafts who as a rule must have the request of fire support cleared by an officer with delays of tens of minutes and sometime hours. And they do so at a fraction of the cost since you need to include the cost per flying hour of the aircraft in your calculation as well as the cost of the air-base.

       So for remote locations as well as to sneak in where an enemy has no heavy weapons it is a great option.

       And tracked artillery against a “competent” opponent would be vulnerable to aircrafts so if it is fighting in that environment it will also require an air umbrella or AA defenses. In a remote location there might be none of that to deal with making the towed artillery’s mobility a even bigger asset.

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       1. “And for remote locations artillery will provide timelier fire than the alternative which will be aircrafts who as a rule must have the request of fire support cleared by an officer with delays of tens of minutes and sometime hours.”

          This is one of reasons that make fast jest useless for CAS – A-10 or ALX can loiter near the front lines, with some A-10/ALX elements responding to CAS requests coming directly from engaged units, others acting as “free hunters” and attacking targets of opportunity (even behind enemy lines – battlefield interdiction is just as important as close air support) and remainer being under control of divisional headquarters.

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    3. “AC-130 just typical USAAF wastefulness and duplication.” – If all air operations where in the air-war front lines the C-130 would be a sitting duck. But in many conflicts you must deal with infiltrators behind your lines or irregulars in your front lines and in those instances the AC-130 can fly high enough to avoid man-portables and deliver rather inexpensive fire support.

       You do not want a huge proportion of your airforce to be made of them but you can use a few.

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    4. “Do you see any advantages that gunship style CAS plane like the AC-130, might have over a more conventional plane? Is there any advantage to circling around the target firing high calibre cannon? `Or is the AC-130 just typical USAAF wastefulness and duplication.”

       I personally don’t see the need for something like the AC-130. It would be very vulnerable in a nation state conflict. It would not be able to maneuver nearly as well to avoid ground fire and incoming missiles. The only maybe advantage is that it could be on station for longer periods of time.

       But then consider the alternatives. For say, 1,000 AC-130s, how many AX-type aircraft could be built?

       I do see the need for a bigger, more powerful version of the AX (for killing ~70 ton MBTs and perhaps heavy fortifications), but it’d be a specialized unit, and you’d still want it as small as possible.

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       1. In low intensity conflict, at night and with air supremacy the current gunships still get shot down. To me they pack the right tools, but in the wrong platform and are too expensive to be procured in useful numbers. They have to operate at medium altitude to avoid small arms, are huge targets and rely on their countermeasures suites to live against manpads or fly higher ( out of effective range of many of their weapons) when the manpads threat is prevalent.

          The WW2 Tsetse Mosquito on the other hand was relatively cheap ( made mainly of plywood), easy to repair, fast and packed a 700kg 57mm cannon with 25 rounds along with crew armour.

          If you take those same qualities and put them in a modern package with a side firing large calibre cannon or similar the results would be interesting to say the least. Clearly a level of stealth, in terms of IR emissions and visibility to the Mk1 eyeball and ear would be necessary. Also visibility / sensors such that the WSO could act as an artillery observer. Fulda lights and an asymentric design, with the engine exhausts not visible from the armoured side might be one avenue…

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       2. That, and how many far more survivable Tucanos/Super Tucanos could be procured for cost of one gunship?

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14. http://foxtrotalpha.jalopnik.com/the-usafs-rationale-for-retiring-the-a-10-warthog-is-bu-1562789528

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16. http://www.pogo.org/our-work/straus-military-reform-project/weapons/2013/the-a-10-warthog-a-core-defense-issue.html

    Sprey Response to Question on Desired Improvements to the A-10: Desired improvements include

    •More thrust to escape target area defenses, but without reducing fuel efficiency to maintain or extend loiter;
    •Tighter/quicker turn around for even faster re-attack;
    •Improved gun with faster spin up rate for the very first rounds (which are always the ones most on target);
    •More variety in the types of gun rounds;
    •Make the entire aircraft smaller;
    •Make aircraft even quieter;
    •Even more flexibility where the aircraft can land/take off to enable closer contact with ground forces.

    [audio src="http://www.pogoarchives.org/straus/a-10/A10Conference_pt2_questions.mp3" /]

    Go to the 15 minute point on the clip above to hear Sprey’s thoughts on an improved A-10

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    1. Yes, all are valid points, but I’m afraid that USAF isn’t interested in designing a new CAS fighter.

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       1. Yep, unfortunately I think you’re right there Picard. I have even more respect for Sprey and others who refuse to give up. One of John Boyd’s Officers felt like things were stacked up way against him. Boyd’s view “you can’t give the bastards a free run, at least make them earn it”.

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       2. Indeed. It becomes even more impressive when you consider that they basically had to use guerilla tactics to get the F-16 and A-10 into production.

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       3. Exactly right. Most books never give Boyd or Sprey a mention for their work unfortunately. No mention that the USAF never wanted the F-16 or A-10 or even that Boyd came in and saved the F-15 from being a 80,000 Ib swing wing to a 40,000 Ib fixed wing.

          I had grown up -perhaps- proud of myself of how much I knew ie. aircraft specs etc…. then I read ‘boyd – the fighter pilot who changed the art of war’ Wow! …In short, it was a re-education. I felt so strongly about what I had just read, I wrote to the author Robert Coram, Sprey, Winslow Wheeler and others. I was so grateful that Boyd’s story was told. It appears I’m not the only one who felt the same way. During an interview, Coram stated that he receives letters from people everyday. People say they read the entire book in one sitting. The interviewer asked why is this happening? Coram said, ‘because of how much boyd did and how badly he was treated’.

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       4. And, ironically, Boyd seems to be respected more in the US Army and USMC than in USAF.

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    2. This aircraft actually fulfills the overwhelming majority of Sprey’s requirements. It’s a smaller, more agile target. That makes it harder to hit. If I recall correctly, the TW ratios are more favorable for this aircraft. It looks to be quite durable. The engines are well spaced and most of the shots to the engine will have to go thought the wing. The other thing to remember is that there is no fuel in the wings in this design. Furthermore, it’s a cheaper aircraft, so you can get more sorties.

       I think that the only thing I disagree with is the use of an electric gatling cannon – it has to be gas operated or use a rotary gun. At the moment, I do not think that there are any 35mm rotary type guns designed for burst firepower. There have been 35mm guns designed for AA, and the highest muzzle velocity of them was a 1400 m/s 35mm gun firing tungsten rounds. I wonder if a higher caliber with some modification could have a good “burst” ability. The goal is to be able to destroy the 65-75 metric ton heavy tanks that permeate through most of today’s armies. Such a weapon does not exist I fear. Of course, the problem is that most armed forces do not understand or remain willfully ignorant of what makes a GOOD weapon for this job or for that matter what makes a good CAS aircraft.

       I think Picard said in one of his other comments he has further revisions planned.

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       1. “I think Picard said in one of his other comments he has further revisions planned.”

          I did, in particular placing engines closer to the fuselage so as to reduce roll inertia, but in the end I decided against it*, so it will remain as it is. Overall, all proposed aircraft seem to be at thier final, with no further revisions necessary.

          *for multiple reasons, first, I realized that it would have placed engines too close to the fuel tanks. I solved that by spacing engines away from fuel tanks, while still in the body, but that again increases roll inertia, and aircraft ended up being larger and heavier than the ALX, so overall inertia was increased as well.

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       2. All tanks have a huge thermal signature. So it is little disadvantage if the M-1 is the highest. This is just a marketing ploy.

          The turbine is better for sustained speed but not as good if you have to accelerate from one spot to another. That the M-1 has been used mostly in a stop-and-go fashion has been a problem.

          If you take out the turbine and replace it with a diesel there will be less space inside for certain things like ammunition.

          The M-1 is very specialized design. Conceived to fight the Soviet Union primarily close to the point of attack projected to have been at the Fulda Gap.

          http://en.wikipedia.org/wiki/Fulda_Gap

          So it was conceived to be close to the action when it occurred so logistic was not so critical, fight on that terrain only (no expeditionary fighting) and quite frankly not expected to survive in great numbers the initial onslaught of the Soviets… just simply buy time. It as well as the Apache and the A-10 where specialized machines for that environment that where latter used in other situations. Of the the three the most flexible and adaptable was the A-10 followed by the Apache.

          But the M-1 is getting old and will have to be replaced. I will bet that with expeditionary fighting in mind it will not be with another turbine engine.

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       3. “All tanks have a huge thermal signature. So it is little disadvantage if the M-1 is the highest. This is just a marketing ploy.”

          There is huge and then there is huge. Tanks often have to be masked, and higher the IR signature, longer does it take for tank to cool off to appropriate level.

          “The turbine is better for sustained speed but not as good if you have to accelerate from one spot to another.”

          True. This means that it is only advantageous on large, flat, open terrain, but is actually an inferior choice when tank has to “sprint” from cover to cover, which is a standard employment tactic in European-type terrain.

          “If you take out the turbine and replace it with a diesel there will be less space inside for certain things like ammunition.”

          M1 doesn’t have much main gun ammo compared to other tanks used by NATO countries (40/42 120 mm rounds, compared to 52 120 mm rounds for Challenger II, 40 120 mm rounds for the Leclerc, 42 120 mm rounds for Lepard 2 and 42 125 mm rounds for M84A4; MG ammo is 900 12,7 mm and 10.400 7,62 mm rounds for the M1, 1.100 12,7 mm and 3.000 7,62 mm rounds for the Leclerc, 4.750 7,62 mm rounds for Leopard 2, so there is that advantage).

          “But the M-1 is getting old and will have to be replaced. I will bet that with expeditionary fighting in mind it will not be with another turbine engine.”

          True, I remember some talk about M1s gas turbines being replaced with diesel engines.

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17. Yep. When Boyd died, his friends didn’t send his papers to the USAF, they sent it to the Marines as they knew the Marines appreciated him more. Even at his funeral, the marines gave him a fitting send off, the USAF didn’t.

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    1. And both US Army and USMC embraced Boyd’s philosophy, which led to quick collapse of the Iraqi military in both Gulf Wars.

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       1. The Republican Guard got away in the First Gulf War. One very serious issue was the flaws in generalship. It’s well .. a mobile city as I described in the other post. The OODA loop is too big.

          The USAF then insisted that it could destroy the Republican Guard through strategic bombing. This failed. I suppose this is something of a modern “Dunkirk”.

          Another was the flaws in the M1 tank. You know the fuel quotes that you get? They are much worse. You see, the M1 tank has the ability on its jet turbine to use all types of fuel. The problem is that when you use anything other than the optimal fuel, the efficiency dropped. I do not know what it was like in the Gulf War I entirely, but after the 2003 invasion in Iraq, the Pentagon was supplying 14 different types of fuel to the US occupation force there.

          By default the M1 uses diesel fuel for its turbine engine. Fuel consumption is as follows (I’ve converted the figures to metric) for the M1A1.
          – Roads: It needs 4.7L to go 1km
          – Cross country: It needs about 16.5L to go 1km
          – Idle: Officially the figures say approximately 38L per hour. In practice in the desert, the figures were 60.6L per hour for an M1A1 during the Gulf War.

          The M1A2 is probably worse because of its higher mass. Each M1 tank has a fuel tank of 495 gallons (1874 litres). You can do the math. Hint: You cannot go very far without refueling. Compounding the problem, the IR signature from this very hot exhaust is very visible.

          JP-8, which is what the M1 used in an effort to standardize fuel reduced the max range by 5%.

          Those figures by the way, are not the worst case scenarios. There’s an old US Naval Institute article published in 1991 about this. I don’t have the link but apparently under some situations, the M1 can use in excess of 21L to go 1 km. Anyways, the tank used up 60% of its 1874L fuel to go 80 km and this was on partial road. This was in actual combat, so perhaps it is more realistic than the figures I put above.

          For a comparison
          – The Leopard 2 (older model, so the 2A7 current model probably has worse efficiency since the mass went up) used about 1 L every 2.35 km. This I think was a mix of road, but mostly cross country.
          – Not sure about idling though. However, the UK’s Challenger 2 uses about 20L/hour at idle. I’d imagine the Leopard 2 would be somewhat higher.
          – Leopard 2 carries a 1160L fuel tank.

          There’s only a few advantages for this gas turbine:
          – A jet turbine has a mass of 5 metric tons less. The Honeywell AGT1500 has a mass of about ~1150kg. The Leopard 2’s diesel is a bit in excess of 6,500 kg.
          – I think modern diesels have a much lower mass.
          – Jet turbines can use mixed fuel.
          – Apparently people have said jet turbines used to be quieter, although modern diesels have caught up.

          Anyways, this refueling effort has created plenty of problems for the US. In particular, the logistics tail is huge.

          I think that the Leopard 2 may have had an upgrade to its engines so the fuel consumption figures may be even more in favor of the Leopard 2. I need to do more reading on this one though.

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       2. “One very serious issue was the flaws in generalship.”

          Another was that US M1 tanks ran out of the fuel while trying to cut off Republician Guard’s line of retreat. That is what you get when you use a system that gives you a minor tactical advantage (nonexistent, really, as Leopard II is just as fast as the M1 without using the gas turbine) for a major strategic disadvantage.

          “You see, the M1 tank has the ability on its jet turbine to use all types of fuel.”

          In other words, just like any multifuel diesel engine used in European tanks.

          “– Apparently people have said jet turbines used to be quieter, although modern diesels have caught up. ”

          But gas turbine can be detected by IR sensors at very large distances, while sound travels for comparably short distances in the air.

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       3. I should also mention that the diesel engines tend to be more reliable than the gas turbine engines used in the M1. It’s become a problem for the tanks.

          I think the desert has also been a problem for the tanks (possibly due to sand being ingested into the engines).

          The Dutch has similar problems with the Pzh2000 as with its diesel engine.
          http://www.pmulcahy.com/self-propelled_artillery/german_sp_artillery.htm

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       4. “By default the M1 uses diesel”

          Oops I think this is a typo. It should be JP-4 that was the original fuel. They swapped it over to JP-8, which became the standard fuel, albeit at the expense of range.

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       5. Yes, by default it uses jet fuel, which is one of reasons why it is used by the US military.

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       6. BTW, I believe that ethanol can be used to power both diesel and jet engines, so that solves logistical issues… jet fighters, turboprop aircraft and ground troops can all use same fuel.

          Only problem would be if your armored divisions started to drink themselves into engine shutdown (though, relistically, there is no danger of that as 100% alcohol can easily be lethal).

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18. What also is interesting is the real cost of the M1 Abrams today. The M1A2 upgrade program went “wildly” overbudget, and the cost of electronics ended up being around ~$6 million USD (in 1990s dollars, so even more today) per tank. Due to the state of accounting, it is not possible to get real costs, but the unit cost of an M1A2 is probably north of $10 million USD.

    The last I heard, as much as 25% of the maintenance budget for all land vehicles in the US Army went to M1 engine maintenance owing to its reliability issues. Another 25% goes to the rest of the tank.

    Another was that US M1 tanks ran out of the fuel while trying to cut off Republician Guard’s line of retreat. That is what you get when you use a system that gives you a minor tactical advantage (nonexistent, really, as Leopard II is just as fast as the M1 without using the gas turbine) for a major strategic disadvantage.

    The only advantages then are the lower mass of the tank (which is more than offset by the huge logistical “tail”), but that has since disappeared, and one I did not write before, jet turbines have a somewhat faster acceleration.

    Really going back to when the tank was first designed, the reasons for adding the turbine were mostly political – to save an in trouble company at the time (Chrysler) over other considerations. The UH-60, AH-64, and SH-60 were supposed to have the AGT1500, but that never happened, so it made things more complex rather than less complex. Chrysler later sold its tank division to General Dynamics, who operates it today.

    In other words, just like any multifuel diesel engine used in European tanks.

    Pretty much.

    Standardization around diesel would bring other benefits. Most vehicles on the ground today use diesel.

    But gas turbine can be detected by IR sensors at very large distances, while sound travels for comparably short distances in the air.

    Yep. There is that. If you ever hear an Abrams, it doesn’t get rid of the other problems noise wise, like the tracks. Actually, they wanted to replace the tracks too with the Leopard 2’s tracks. That and the diesel got put off for political reasons.

    The M1’s turbine puts out about 4 times more heat compared to a diesel (which makes sense when you consider fuel consumption figures). This is actually a bigger problem then it sounds. It’s easier to find it with IR sensors and worse, IR guided missiles. The other problem is that when you move your tank and put it into a position to ambush, it takes much longer for the tank to cool down after you idle the engine. Considering the heat, someone once joked that you could have a jet fighter fire AAMs and they would probably home in on the Abrams due to the immense heat that it gives off. This could be a problem though for ATGMs.

    You will notice that most infantry these days do not “hitch a ride” on the back of a tank these days. That’s because the hot exhaust would make it too dangerous to do so.

    Basically there’s no reason to use a gas turbine today. It’s a terrible decision that is mostly for political reasons. The US Army has attempted to argue though that the cost of upgrading to a diesel would cost more than keeping the status quo for the 8,000 or so tanks (of which I think around 6,000 are in service).

    Interesting article on costs:
    http://www.defensemedianetwork.com/stories/abrams-dieselization-project-doing-the-math/

    I get the impression though reading that they are trying to drag their feet on diesel.

    BTW, I believe that ethanol can be used to power both diesel and jet engines, so that solves logistical issues… jet fighters, turboprop aircraft and ground troops can all use same fuel.

    Only problem would be if your armored divisions started to drink themselves into engine shutdown (though, relistically, there is no danger of that as 100% alcohol can easily be lethal).

    Ethanol has a lower energy density. Chemically, adding an “OH” group at the end drastically lowers the density – by as much as 30%. That makes it problematic for aircraft.

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    1. “The last I heard, as much as 25% of the maintenance budget for all land vehicles in the US Army went to M1 engine maintenance owing to its reliability issues. Another 25% goes to the rest of the tank. ”

       I knew it was bad, but I didn’t expect that.

       “jet turbines have a somewhat faster acceleration.”

       From what I know, tanks with jet turbines have higher top speed but slower acceleration.

       “If you ever hear an Abrams, it doesn’t get rid of the other problems noise wise, like the tracks”

       I watched some videos of M95 Degman, and tracks made almost as much noise as the diesel engine.

       “Considering the heat, someone once joked that you could have a jet fighter fire AAMs and they would probably home in on the Abrams due to the immense heat that it gives off.”

       Well, it does have what is basically a jet engine in its a**.

       “Ethanol has a lower energy density. Chemically, adding an “OH” group at the end drastically lowers the density – by as much as 30%. That makes it problematic for aircraft.”

       Took a look… ethanol has density of 0,789 kg/l and energy density of 26,8 MJ/kg, while jet fuel has density of 0,804 kg/l and energy density of 43 MJ/kg. So for the same fuel volume, ethanol is 61% as energetic as jet fuel.

       So not a good choice for jet aircraft, unless you are desperate. Not sure about prop aircraft, though.

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       1. They did a study about it. The Defense Science Board Task Force on Improving Fuel Efficiency of Weapons Platforms is the name of the study.

          Anyways, fuel consists of an estimated 70% of mass of logistics in the US military. Anyways, a 50% increase in fuel efficiency would lead to a 20% faster buildup during the Gulf War, which would have meant they could have fought 1 month earlier. A diesel engine could reduce fuel consumption by as much as 75%.

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       2. And had they bought A-10s and some turboprop FACs instead of B-1s, B-2s and B-52s…

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    2. That being said, biofuel is an option.

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    3. http://www.rechargenews.com/news/biofuels/article1284123.ece

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       1. Well, they are retiring the A10, so I guess that project will probably be put on hold unless there’s another aircraft being tested. The question is all about the Energy Return on Investment of biofuels.

          Fascinating thing about the fuel consumption of the US military was how it influenced the insurgency after the 2003 invasion. It became apparent that the US was very reliant on its long tail. Anyways, insurgents deliberately attacked the logistics vehicles. Compounding the problem, the US in response to mines (IEDs) had to up-armor its existing vehicles or replace them with heavier mine resistant vehicles, which in turn drove up fuel and spare parts even more. The network of pipelines, supply trucks, etc, proved very vulnerable. The other issue is, you cannot defend everything unless you have truly overwhelming numbers.

          Article that might be worth reading:
          http://www.theatlantic.com/magazine/archive/2005/05/gas-pains/303897/

          I’d bet it’s even worse than since 2005 when that article was written as time went on. That and the more force you use, the more you anger the local population. This ISIS takeover is just the latest blowback in Iraq.

          From what I know, tanks with jet turbines have higher top speed but slower acceleration.

          To be honest, it doesn’t really matter. Jet engines are not good for tanks either way.

          Getting the power to weight ratio up may be the way to get good tank performance. Alternatively, maybe a hybrid-electric drive could work. It would save a moderate amount of fuel and provide extra power where it is needed.

          I watched some videos of M95 Degman, and tracks made almost as much noise as the diesel engine.

          Standing near a moving tank in real life (Leopard 2), the best way to describe it would be sounding like a diesel locomotive, only with the noise of tracks instead of rails.

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       2. “This ISIS takeover is just the latest blowback in Iraq. ”

          True, though it isn’t just about force. US used Iraq as a social experiment for extreme neoliberal approach, and that is what caused insurgency in the first place. But of course, it is easier (and more profitable for capitalists) to blame it on Al Quaeda instead of admitting that, just maybe, their own approach was wrong. Try to find Naomi Klein’s “Shock Doctrine” for a more detailed overview.

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       3. Yeah I read it. A lot of Americans I have noticed don’t understand why there’s so much anti-American sentiment in South America. Well … it’s not entirely without justification I fear, that sentiment. I don’t think they will understand why relations are so tense between Iran and the US too (hint: in 1953, the US helped overthrow their government for oil).

          Domestically, you can definitely see that doctrine coming into the Western world. Inequality in the US especially, the rise of gated communities, the decline of infrastructure, and other trends described in the book.

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19. @HGR

    The issue is that the M1’s thermal signature is 4 times bigger. Thermal signature is roughly going to be proportional to fuel consumption. For similar reasons, large fighters are more likely to be detected first. Bigger engine = more fuel = easier to find on IRST.

    The problem is, it makes it easy to find a tank that emits a bigger thermal signature. That makes it easier to get the first shot off. It’s always about being the first to detect the enemy and first to fire.

    During the Gulf War, a T-62 managed to take out 2 M1A1 tanks. The tank commander was very smart. He kept his engines off, and he did not get out to expose himself or his crew. Tanks that left their engines on were quickly taken out. Tanks that left their engines off but had a guy standing outside to see were also taken out. Ir sensors are good enough to see people a couple of km away provided nothing covers the horizon. The easy solution was to shoot at their “feet”. That by the way, is one of the reasons why I’m unsure about open top designs. The crew of that T-62 stayed inside the tank and hand cranked the turret to aim. He killed 2 M1s before the heat of the gun barrel gave him away.

    Since the past 20 years, IR sensors have gotten better.

    There are other problems. Even with the engine off, the sun can heat the back of a tank and warm up the tank. That can make it visible to IR sensors, especially if you are talking after sunset. There’s got to be something on the tank to prevent that.

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    1. “Gulf War, a T-62 managed to take out 2 M1A1 tanks” – first time I have ever heard this. Taking out a heavy tank like the M-1 is relative expression. Most of the time they are disabled and unable to continue.

       They are working on Diesel engines for the M-1, That is according to Wiki and I have read so in other forums. But there has been no action yet. I think they view something like this Diesel engine as a stop-gap solution until something else comes along that will be the definite replacement. But one thing we know is that the Army does not want any more M-1s but I have not read anything solid about a future heavy tank. I know they would like something light and transportable by C-130.

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       1. He shot at the side armor of the M1.

          Anyways, if you want details, this is a good book about it:

          The point is, a tank like the M1 can be taken out with hits to the side or rear. Mines can take out a tank from below, and aircraft can hit a tank from the top.

          The thing about tanks is for all the talk about tanks being obsolete, one question becomes, replace it with what? You still need an armored vehicle on the ground to fight. Aircraft have their limits in this regard. And obviously soldiers are not going back to 100% foot slogging nor can they rely solely on wheeled vehicles.

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20. Pingback: NATO air forces proposal 3 « Defense Issues

21. Some interesting links:

    http://www.thedailybeast.com/articles/2014/10/12/american-warplane-s-forgotten-nazi-past.html#

    View at Medium.com

    View at Medium.com

    I can also highly recommend the 3 book series ‘Flying Guns’ (WW1 / WW2 / Modern Day)
    by Anthony G Williams and Dr Emmanual Guslin.

    These are not light weight by any means. They concentrate on the guns, the ammo. HUGELY detailed. Detailed tables with formulas to show the difference (for example), SU25 gun vs A10. Turns out a Frogfoot’s 30mm round has 80% of the power of the Warthog’s 30mm. On top of the that, the A10 carries 5 times as many rounds so is in effect 6 times more destructive (not including weapons under the wings).

    Sprey has commented that in a follow-on A-10, that the same proven GAU-8a ammunition be used with an aim for greater variety of types of ammo be available for different requirements. No doubt, the aim is to use the same ammo put in a smaller package as a follow on A-10 at 50% the size is attractive.

    I’m quite open to a best of both worlds type situation. Frogfoots revolver gun setup with GAU-8a ammo as long as the follow A-10 could take out just as many tanks with the gun or more.

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    1. To be honest, I think that a custom designed gun might be needed for a truly ideal CAS aircraft – maybe higher calibre, but also high calibre guns run now don’t have the spinup time needed to be truly great.

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22. Opps – the other links didn’t come through…
    View at Medium.com
    View at Medium.com

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23. View at Medium.com

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24. Search on:
    1. war-is-boring/pilots-plan-tomorrows-a-10
    2. war-is-boring/stuka-and-sturmovik-the-aircraft-that-inspired-the-a-10

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    1. Comments with links typically require me to approve them in order to prevent spam. But if they don’t come through, do remind me as I may miss them among other comments.

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25. @Picard,

    Rudel was a pretty firm Nazi believer.

    Most of the military though not. Some like Erich von Manstein and Gerd von Rundstedt were openly disdainful of Nazi ideology. The majority of the Waffen SS would have preferred if their units were disbanded and to fight as a part of the regular army.

    A very high proportion of U-boat crews were pro-Nazi.

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    1. Rommel also didn’t care much about Nazi ideology, and in fact most of the Army as well as much of the surface navy continued tradition of Prussia and Imperial Germany. One commander of a German cruiser (can’t remember the name) covered himself in the Imperial German flag before shooting himself when his ship was interned in Argentina.

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    2. That was Hans Langsdorff and the ship was the Admiral Graf Spee, a cruiser that had been noted for its honorable conduct. He scuttled his ship and committed suicide, hoping to spare his crew after it had been heavily damaged.

       But yes, most of the top commanders did not care for the Nazi ideology.

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       1. Thanks, I’ve forgotten the names.

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26. One of the big issues that I see is that with a lack of CAS becoming a priority, this means in turn that the R&D money has been spent elsewhere.

    Areas of improvement I could see are:
    1. A fast spin-up high calibre gun, firing tungsten sabot and various selectable rounds
    2. Improving reliability and flight to maintenance ratios (it will be incremental)
    3. Improving the ability to further operate off fields
    4. Lightweight armor (could be used in light vehicles too) – could use material sciences here

    The other is that there has never been the kind of extensive testing of a real world CAS aircraft against battle damage either. We have the A-10 Gulf War and 2003 invasion performance (basically the only times they faced moderate to heavy AA) and perhaps the Su-25 reports from Russia’s actions. Historically for example, hydraulics were a vulnerable point in many aircraft. I think that with more extensive testing, a more survivable design than what we currently have is possible.

    The issue is that R&D money has been allocated to areas that are not so useful and there isn’t the priority on things like CAS, which many air forces don’t care about.

    I suspect that with real money invested, it would end up like cars, seeing improvements of modest rates with each new generation.

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    1. “1. A fast spin-up high calibre gun, firing tungsten sabot and various selectable rounds”

       I’m probably going to use revolver gun in my next proposal. Will see; now that FLX is finished with only minor cosmetic changes possible in the future, I’ll be able to give more attention to the ALX.

       “2. Improving reliability and flight to maintenance ratios (it will be incremental)”

       Yes, that is quite important.

       “4. Lightweight armor (could be used in light vehicles too) – could use material sciences here”

       Composites and titanium come to mind. Some kind of multilayer armor could work.

       “Historically for example, hydraulics were a vulnerable point in many aircraft. I think that with more extensive testing, a more survivable design than what we currently have is possible. ”

       Any CAS aircraft will have to be aerodynamically stable, to allow hydraulic and mechanical control systems to be used. FBW simply won’t work there.

       “The issue is that R&D money has been allocated to areas that are not so useful and there isn’t the priority on things like CAS, which many air forces don’t care about. ”

       Indeed. Croatia for example has retired basically its entire CAS capability (Mi-24) with no replacement in sight. USAF is trying its best to kill the A-10, and other NATO air forces don’t have any CAS capability to begin with.

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    2. There hasn’t been the kind of testing needed to see if this will work out. That’s the issue.

       Another is how quickly can a CAS aircraft be repaired by battle damage.

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    3. Sorry to respond to such an old post, but I only found out about this blog a few weeks ago, and this is the only place I can go to for such informed commentary.

       1) Is it even possible to produce a machine gun that fires Sabot rounds? I was under the impression that Sabot rounds basically needed to be the size that they are to penetrate MBT armour, so you would basically need a tank cannon, which I think is too large for a plane. Also you’d need a 500kg autoloader so that seems out of the question. The only way I think this would work is if you could build very thin sabot’s that didn’t fly very far, but use the plane to overcome this limitation by firing closer (because it’s a plane).

       2) Yes of course, although at least the engines are much more reliable and fuel efficient than even in the 1970’s.

       3) Yes, stronger landing gear especially seems like a must.

       4) I think everyone first thinks that lighter armour would be better and I was thinking this myself, until I read an article where and A-10 pilot was discussing how to improve upon the A-10 and he said that you can’t use composites because the plane needs to be able to be quickly patched up since it gets so many holes poked in it. I think we can probably do better than steel, maybe use the aluminum alloy found in the M113? Someone with more materials knowledge than me can answer this but the point is that it also needs to be cheap and easy to patch in the field.

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       1. It is absolutely possible and has been done numerous times before in the form of 50BMG SLAP, Steyr’s 15.2×169mm, the A-10 fire saboted penetrators as standard.
          Titanium seems to be the go for aircraft armour at this point

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27. I would hesitate to guess that the best way to design a CAS aircraft may be similar to the A-10:

    Define role (ex: tank destroying).
    Design the gun (unlike A-10, we will want faster spinup time).
    Incorporate all lessons of the least.
    The aircraft, like the A-10 would be designed around the gun.

    The reason being it’s a high caliber gun that is the main weapon of the CAS aircraft.

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    1. Yes, that is the optimal way. I’m actually using it on my next proposal – utilization and gun are defined already.

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    2. Oops “least” should have been past. But yeah, past lessons.

       That’s actually a problem now because with CAS getting so little priority, it’s harder to draw upon past lessons. We do have the WWII era, the various US A-series, and Russian experiences, along with what nations deploy attack helicopters (not as useful for fixed wing aircraft).

       I have wondered if a good passive IR sensor could be used for detecting moving tanks. Particularly for tanks that use gas turbines, but even diesel tanks, it might work out. It would be operated by the person in the rear. It would not replace the eyeball, but it would complement it, especially for camouflaged targets.

       But engines on top, rear as you’ve noted elsewhere is probably the way to go. Pierre Sprey originally wanted a thrust to weight of around 0.85 at 50% fuel for his Blitzfighter proposal. I’m not sure how that would be accomplished though, even with the engines of today offering a better thrust to weight ratio than they did – that would mean deleting armor or something else.

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       1. “That’s actually a problem now because with CAS getting so little priority, it’s harder to draw upon past lessons. We do have the WWII era, the various US A-series, and Russian experiences, along with what nations deploy attack helicopters (not as useful for fixed wing aircraft).”

          That is true. However, lessons from World War II are useful even for modern air superiority fighters. More things change, more they stay the same – basic principles never change, only tools do. Usage of aircraft did not revolutionize warfare, you still need troops on the ground to win, but just like always, people get excited about new toys. Douhet was an idiot, but idiots of that type are typically dime a dozen, how many times did you hear about “revolution in warfare”, “revolution in military affairs” etc.?

          “I have wondered if a good passive IR sensor could be used for detecting moving tanks.”

          Yes, especially at night and if there are no obstacles. At day, and in hotter environments, ground reflection may mask diesel tanks’ emissions (gas turbine tanks have a jet engine in the back, so anything other than surface of the Sun will not be a problem; and if you’re on surface of the Sun, you’ve got bigger problems than CAS aircraft trying to shoot you). I’d like to know if there were some studies on the topic though, and modern IIR sensors can detect things that are cooler than the environment just as those that are hotter than it.

          “Pierre Sprey originally wanted a thrust to weight of around 0.85 at 50% fuel for his Blitzfighter proposal. I’m not sure how that would be accomplished though, even with the engines of today offering a better thrust to weight ratio than they did – that would mean deleting armor or something else.”

          Actually, it is achievable with modern engines if you put a large engine into small comparably short-ranged aircraft. And since Blitzfighter would be colocated with troops, there was no need for it to be long-ranged.

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       2. So basically a point defense sort of CAS aircraft (versus one with hours of loiter).

          What kind of fuel fraction then would have to be sacrificed? Also, if it was 0.85 in the mid-1970s, I’d imagine 1 to 1 at 50% fuel today would be the equal as engines have gotten better in terms of efficiency, mostly due to higher inlet temperatures.

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       3. Type “Blitzfighter” in Google, there are some good designs shown. Blacktail on Deviant Art has good drawing and description of a Blitzfighter design as well.

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       4. And yes, it is point-defense as it is supposed to be colocated with troops.

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28. I was reading, “Boyd,” by Coram, when I noticed something interesting about Sprey’s original A-X proposal.
    
    A one engine plane.
    Seeing as Sprey was pretty much a purist/absolutist in almost, if not everything, he did; why go for a single engine? Sure, it would be simpler and smaller, but you would have more trouble fitting a big gun on the inside, and you’d have to armor the engine up because you don’t have any redundancy.

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    1. Engine has to be armored anyway. Single engine means smaller, cheaper and easier to maintain, which increases number of aircraft in the air. It also means better endurance for given fuel fraction (one 30 kN engine is more efficient than two 15 kN engines), as well as better agility and maneuverability due to smaller size and different distribution of mass; consequently, what you lose in ability to survive hits, you gain in ability to avoid getting hit in the first place. However, it may reduce fuel fraction and it also reduces thrust-to-weight ratio, leading to lesser ability to recover energy.

       Personally, I’m still not decided on the number of engines a CAS aircraft should have.

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29. Regarding a lighter, less-barrelled version of the GAU-8 Avenger that runs 30x173mm it would be ironic to the utmost by resurrecting the GAU-13/A and building the plane around it: https://en.wikipedia.org/wiki/GAU-13 . This was the gun that the Air Force tried to kill the A-10 with in their attempts to cram it into a gun pod and put it onto F-16s.

    Rate of fire is only 2400RPM, however, gun weight is 151kg, a little over a half that of the 281kg of the old Avenger. This halves the throw weight per one second burst, but the weight savings are quite significant. Lower rate of fire also means less recoil and vibration, which translates to less internal bracing required, which alters the balance of the aircraft and requires less ballasting. It’s a virtuous cycle.

    If it is not weight, but recoil that is the issue, then one can exceed the throw weight of even the GAU-8 by using dual GIAT-30 cannons. At 120kg per GIAT-30, 2 gives 240kg, each firing at 2500RPM. Combined rate of fire 5000RPM which easily tops the 4200RPM (nominal) of the Avenger. It should be noted that in order to extend barrel life, the Avenger’s rate of fire was later dialed down to 3900RPM. Dual GIAT-30 in this case would then easily surpass that of even the Avenger in terms of throw weight, if not in muzzle energy. The Mirage 2000 mounted dual DEFA 30mm revolver cannons were later upgraded to GIAT-30s. So the prospect of having massive throw weight without excessive penalty in terms of internal bracing or having to build the entire platform around the gun is very much achievable. I don’t see 35mm+ caliber aircraft guns arising any time soon, so I think throwing down as much projectile per unit time matters more.

    Regarding the wing shape, have you considered an elliptical planform? It might allow you to have a shorter span, which aids in road basing and I suppose carrier ops. It is harder to construct (added costs), but the added efficiency at low speed would help endurance, and it might shorten the take off run (also good for rough field or road basing). http://quest.arc.nasa.gov/aero/events/collaborative/help.html

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    1. Issue with GAU-8 is weight and size, I wanted an aircraft smaller than A-10 which in turn meant smaller and lighter gun had to be used. I’m planning to redo the proposal as two aircraft: heavyweight one with 35 mm Oerlikon KCA, and a lightweight one with GAU-13/A, but it will be a while before I get around to it.

       Thanks for suggestions.

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       1. I think that having a truly “Heavyweight” aircraft gun at 35mm leaves much to be desired in terms of ammunition carriage and rate of fire. The Oerlikon 35mm Millenium gun https://en.wikipedia.org/wiki/Rheinmetall_Oerlikon_Millennium_Gun fires at 1000rpm. It is not designed for aircraft use. The Oerlikon KCA also has a relatively low rate of fire at 1150RPM. When you have a strafing run with a window of only 1-2 seconds, rate of fire matters more than sheer caliber, and muzzle energy is probably a better determinant of effectiveness than caliber (although higher caliber usually means more muzzle energy, this also depends on the cartridge).

          Here is a table of 30mm caliber munitions from an ammunition collector: http://www.quarryhs.co.uk/30mm%20cannon.htm (Scroll down to bottom). The difference between GIAT-30 30x150b muzzle energy and the 30×173 PGU-13 series is pretty significant: 144000J versus 210000J, for a delta of ~46% within the same caliber.

          One of the most interesting parts of this munitions collector’s site though, was this table here: http://www.quarryhs.co.uk/modern_fighter_gun_effectiveness.htm

          The table attempts to normalise aircraft guns by momentum (mass x velocity) and percentage high explosive filler in order to get an overall efficiency for the cartridge. The second table is particularly pertinent as it then attempts to get an efficiency calculation per unit weight when the gun is taken into account.

          The most interesting result is that the analysis puts the super light-weight (but fragile), medium velocity Soviet aircraft guns on the top of the pile. I think there’s something there. In fact Mr Williams rates the Russian 30x165mm as the best overall general purpose ground attack cartridge, having a good compromise between explosive filler and momentum. For air superiority, he rates the 30x150b GIAT-30 as the best.

          Imagine if the MiG-27, mounting that monstrous G-Sh-6-30, were properly designed for ground attack and built around it. Or a platform like your AX mounting it. You have the advantage of cheap Soviet-bloc ammunition (or you can produce your own loading with more efficient projectiles and higher pressure), and a good compromise between ammunition stowage and firepower. Powders these days are much more powerful than those used in the Cold War. The 30x165mm is lighter than the 30×173 PGU-13 series, with similar projectile weight. Gas operation reduces reliance upon electric grid of the aircraft and allows maintenance that is less dependant upon a high-tech infrastructure while also reducing spin up time. A lighter, more compact gun means more can be devoted to internal bracing and ammunition stowage and armour.

          Thinking more about the wing planform, a straight tapered wing might be a better compromise between low speed efficiency and repairability/manufacturability. The elliptic wing, though the most efficient, might be difficult to fix in the event of battle damage; whereas a straight taper gives some of the qualities of the elliptic wing without sacrificing production or repair imposition overmuch: http://history.nasa.gov/SP-367/f13b.htm

          Regarding a further split into heavyweight and lightweight ground attack aircraft, each with different guns and ammunition, that in my view makes the AX/ALX even less palatable to the Generals of today. They are no longer contemplating high-intensity combat between nation states; which is why they are so complacent and wallow in inefficiency. Further speciation at some point introduces diminishing returns on logistical footprint and sortie generation.

          If I were to make specialisations, it would instead be based upon a common airframe, with a common gun. The difference maker being single-seat versus dual seat. The single-seat variant focuses on being cheap and maximum payload with the minimal of avionics and jamming to survive IADS. The dual seat variant would incorporate a WSO and additional avionics for datalink or operate as FAC, while having some hardpoints devoted to things like laser designators to serve as terminal guidance for munitions or reconnaissance, or strip almost everything, including some armour to mount a big radar and extensive sensors to function as mini AWACs. The target loiter times of AWACS and CAS aircraft do not diverge so much as to simply put more mini-AWACs up into the sky instead of putting one massive one that then also has to have long loiter time. It also decentralises decision making for resilience.

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       2. “I think that having a truly “Heavyweight” aircraft gun at 35mm leaves much to be desired in terms of ammunition carriage and rate of fire.”

          Agreed, that is one of reasons why I am still far from decided on the issue.

          “and muzzle energy is probably a better determinant of effectiveness than caliber ”

          I did a comparison between GAU-8 and KDG 35 mm as a part of preliminaries for Heavy CAS fighter proposal (don’t expect it before summer, though, if even then). Light CAS fighter would use GAU-13.

          Gun: GAU-8/A / Oerlikon KDG Millennium GDM-008
          Caliber: 30 mm / 35 mm
          Gun length: 2,85 m / 4,11 m
          Gun weight: 281 kg / 450 kg
          Rate of fire: 4.200 rpm / 1.000 rpm
          Time to max RoF: 0,5 s? / 0,05 s
          Rounds in 0,5 seconds: 17 / 8
          Rounds in 1 second: 52 / 16
          Rounds in 1,5 seconds: 87 / 24
          Rounds in 2 seconds: 122 / 33
          Weight in 0,5 seconds: 6,12 – 7,31 / 3,04 – 6 kg
          Weight in 1 second: 18,72 – 22,36 / 6,08 – 12 kg
          Weight in 1,5 seconds: 31,32 – 37,41 kg / 9,12 – 18 kg
          Weight in 2 seconds: 43,92 – 52,46 / 12,16 – 24 kg
          Muzzle velocity: 988 – 1.070 m/s / 1.050 – 1.440 m/s
          Range: 3.660 m / >3.500 m
          Bullet flight time 1.000 m: X / 0,73-1,05 s
          Bullet flight time 2.000 m: X / 1,54-2,34
          Bullet flight time 3.000 m: X / 2,38-3,98
          Bullet flight time 4.000 m: X / 3,34-6,06
          Muzzle energy: 199,2 – 212,4 kJ / 379,7 – 413,4 kJ
          Armor penetration: 38 mm @ 1.000 m / 90 mm @ 1.000 m / 90*
          Max. recoil: 14,87 kN / 6,89 kN

          Basically, KDG has better muzzle velocity, muzzle energy and armor penetration while GAU-8 has better rate of fire, throw weight and ammunition capacity.

          “The difference between GIAT-30 30x150b muzzle energy and the 30×173 PGU-13 series is pretty significant: 144000J versus 210000J, for a delta of ~46% within the same caliber. ”

          Not surprising, seeing how GIAT 30 is designed for air-to-air work first and foremost.

          “The most interesting result is that the analysis puts the super light-weight (but fragile), medium velocity Soviet aircraft guns on the top of the pile. I think there’s something there.”

          Russian fighters are designed to be capable of both air-to-air (dogfight) and ground attack missions. Hence better ground attack performance of Soviet guns compared to Western air-to-air optimized guns.

          “Imagine if the MiG-27, mounting that monstrous G-Sh-6-30, were properly designed for ground attack and built around it.”

          Sounds nice.

          “Regarding a further split into heavyweight and lightweight ground attack aircraft, each with different guns and ammunition, that in my view makes the AX/ALX even less palatable to the Generals of today.”

          Seeing how they don’t want any proper CAS platforms anyway, that doesn’t really matter. And I’m not sure wether a lightweight aircraft is necessary seeing how OLX is also capable of CAS, but on the other hand, I’m not sure OLX can survive serious air defenses. In that case, lightweight CAS fighter has the advantage of smaller logistical footprint, easier forward basing and greater numbers, while heavyweight aircraft has the advantage of greater range and loiter time, heavier payload, better armor penetration with gun.

          If they can tolerate four different stealth fighters (three F-35 “variants” differ enough from each another to be counted as completely different aircraft), two CAS platforms should be manageable.

          “Further speciation at some point introduces diminishing returns on logistical footprint and sortie generation. ”

          Which is the main reason why I am not so keen on the idea myself. My ideal force would be one air superiority fighter, one ground attack aircraft, one COIN/forward observation aircraft, one scout UAV, one strategic transport, one tactical transport and one tanker type.

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       3. In my opinion, the Ground attack and COIN/FAC aircraft could probably be based around a common airframe. See the A-10 and the Pucara. They both have served in FAC and the CAS role.
          In both cases, the essence of the craft is a big gun, good situational awareness, high survivability through armour and agility and having long loiter times. Hence my suggestion of a “heavy” variant that is single seat, emphasising hardpoints and payload; and a “light” variant, that forgoes some weapon carriage for more avionics and dual seating (for WSO), but retains the Big Gun.

          If a Forward Observer is close enough to the front to be calling fires, then it is close enough for battlefield interdiction; and ditto for CAS. It needs to be survivable against IADS because it will be flying low and in reach of SAMs and AAA. The most reliable and precise CAS is with an aircraft mounted gun. So you may as well give the FAC craft a formidable armament. It will need a gun for self defense anyway. Might as well be a big one.

          So: base the airframe around something like the G-Sh-6-30 firing 30x165mm; or if restricted to Western Bloc munitions, then dual revolver cannons based around the Oerlikon KCB 30x170mm or KCA 30x173mm cartridge. I favour the G-Sh-6-30 for weight reasons.

          For greater ammunition carriage, a custom cartridge may be required, like that of the PGU-13 series wherein a plastic driving band and aluminium case is used for saving weight. I personally favour building the airframe around the G-Sh-6-30, or a ruggedised version that fixes the vibration issues. The ammunition is there, and the sacrifice in muzzle energy is arguably worth the weight savings. It should also be noted that the G-Sh-6-30 is “sawn off”; that is, it has shortened barrels to save weight and reduce velocity. A longer barrel arrangement could very well increase muzzle energy to the point that it is competitive with 30x173mm, at much lighter weight than Western bloc guns. Carriage of 1500 or more rounds in an airframe a full 2-3 tons lighter than the A-10 would not be inconceivable. Rate of fire should be limited to 4000RPM to reduce recoil forces.

          Assuming a round weight of ~850g (data here: http://www.arcus-bg.com/products/ammunition/2_30mm_2a42/ap-t_sting/23main.htm) 1500 rounds weighs 1275kg.

          Survivability would be through an equivalent of Thales SPECTRA and armouring. In today’s environment, it may be necessary for the airframe to withstand up to 30mm AAA fire, especially now that both East and Western blocs have moved beyond 20-25mm. A smaller airframe helps, as does use of composites. What is interesting to me was the survivability of the Pucara in this anecdote on wikipedia: https://en.wikipedia.org/wiki/FMA_IA_58_Pucará

          “On 21 May a Pucará was lost to a Stinger SAM fired by D Squadron SAS (the first Stinger launched in combat) [17] and another to 30 mm cannon rounds from Cmdr Nigel “Sharkey” Ward’s RN Sea Harrier,[18][19] the latter after leading a successful two-aircraft raid on a shed allegedly used as an observation post by British forces. The aircraft was surprisingly tough, as Ward observed no fewer than 20 cannon hits before the target started to fall to earth”. Given that the 30mm ADEN cannon is no joke, this suggests that good old duralumin is strong enough even before the gains from composites are factored in. This would have a positive effect on costs; however, armouring will drive weight up and payload down, so some composites will likely be needed.

          Regarding the planform, a slightly tapered wing would achieve better wing area for the weight, while increasing fuel and/or landing gear stowage space. I would follow the A-10’s design cue of putting the landing gear in fairings near the wing root, folding forward with some protrusion to provide protection in belly up landings.

          Some of the avionics or defensive dispensers can go in the tailfin root. I would also favour an integral IRST and/or FLIR for day/night operations. A LIDAR could be useful in terrain following for avoiding IADS through terrain masking. The 2 seater variant would mount more avionics and radios for the purpose of FAC work.

          I don’t have much knowledge of engines so I won’t equivocate there.

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       4. “In my opinion, the Ground attack and COIN/FAC aircraft could probably be based around a common airframe. See the A-10 and the Pucara. They both have served in FAC and the CAS role.”

          They could, but with COIN aircraft you need numbers more than firepower and survivability; with CAS aircraft, survivability and firepower are more important than numbers (though numbers still matter). As far as CAS/FAC goes, you will notice that my “CAS fighter” can in fact serve as a FAC aircraft as well, whereas FAC aircraft is actually optimized for COIN role. You see, FAC aircraft are typically tasked with finding targets, but in COIN environment targets are too fluid for it to wait for a CAS fighter to engage. Thus FAC needs to be able to attack targets by itself.

          Rest of it I mostly agree, but I see no need for LIDAR/FLIR/IRST – night vision is more than adequate there, and when not, a pod can be used.

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       5. The problem I see with podding a FLIR or IRST is that it cuts into the number of hardpoints, and that it is more imposing on the rest of the craft. Podded avionics require their own power supply and environmental shielding, and require some wiring work to integrate with the aircraft mounting it. So you may as well save some weight and drag and engineering work and make it integral. A-10 pilots in Desert Storm used their thermal seeker AGM-65 Mavericks to act as a poor man’s FLIR when conditions restricted visibility and impacted easy identification of ground targets. They did this until the Air Force caved and qualified the LITENING pod for the A-10.

          I can understand the allure of the austere, “purity of purpose” angle you are going for with the AX. It must be said, however, that neglecting IR sensorium could well be penny-wise, and pound-foolish.

          About the COIN/FAC aircraft, I would tend to agree with you that a armed trainer / very light attacker / FAC a la Tucano / Super Tucano has its place in low intensity conflicts. I guess where we diverge is in the proposal – given the known quantity that is the Tucano and your FAC craft’s similarity to it I am puzzled that you would choose not to simply use the Tucano. The other thing is the choice of gun – only 2 50 cals. This is nowhere near sufficient for operating in today’s threat environments. For police work and interdiction of narcotics as part of border patrol, sure. But against insurgents that will likely be fighting from foxholes and sandbagged emplacements, 2 50 cals aren’t going to achieve much. Dual BK-27 revolver cannon in each wing will allow it to really go to work against technicals, mortar pits and emplacements.

          The other thing is sensors. If COIN/FAC craft are required to find opponents, then why skimp on the sensors? A persistent FAC, mounting thermals / FLIR would have been a godsend in Afghanistan, where jihadists would plant their IEDs at night. A strong deterrent to mining roads simply did not exist despite extensive use of Predator drones with Hellfires. In the end, old artillery shells wired to simple pressure switches consisting of wooden planks and spring steel bound up millions of dollars of combat assets within helicopter-supplied FOBs. That is a tactical and strategic failure that something like your COIN craft could have obviated – but restricting COIN operations to daytime, or requiring observers to rely upon NVGs without magnification or depth perception also does not help.

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       6. “I can understand the allure of the austere, “purity of purpose” angle you are going for with the AX. It must be said, however, that neglecting IR sensorium could well be penny-wise, and pound-foolish. ”

          Agreed. But AX is intended mostly for low-level CAS (aircrfat up high miss too much of what is happening due to straw view nature of sensors such as radar or FLIR), so I believe that standard night vision googles are appropriate for the most part. Another reason is that AX is a ground attack aircraft. Normal IRST is optimized for air-to-air role – mounted on the upper surface of nose, with either only LWIR or dual MWIR/LWIR channel. But a sensor for ground attack aircraft would have to be mounted on lower surface of nose and work in either MWIR or, preferably, dual SWIR/MWIR channel. You can see the issue right there – ideal location for sensor is also the only practical location for the gun. Mounting it on the upper surface is possible, but that restricts pilot’s view from the cockpit as well as sensor’s own view of the ground. So I really don’t see any option other than pod (or maybe integrated into a pylon or wing – but I don’t know any SWIR/MWIR sensor small enough for that).

          (This gives an overview of SWIR: http://www.sensorsinc.com/technology/why-swir ).

          “I guess where we diverge is in the proposal – given the known quantity that is the Tucano and your FAC craft’s similarity to it I am puzzled that you would choose not to simply use the Tucano.”

          I’m not sure Tucano is in production any more, and Super Tucano has many gadgets that I didn’t want in a COIN/FAC aircraft. You’ll also notice that OLX is using Super Tucano’s engine, which is more powerful than Tucano’s, while having weight and dimensions below those of Tucano. And due to having four .50 cals instead of two, it has about twice the inherent firepower of Super Tucano.

          “The other thing is the choice of gun – only 2 50 cals. This is nowhere near sufficient for operating in today’s threat environments. For police work and interdiction of narcotics as part of border patrol, sure. But against insurgents that will likely be fighting from foxholes and sandbagged emplacements, 2 50 cals aren’t going to achieve much. Dual BK-27 revolver cannon in each wing will allow it to really go to work against technicals, mortar pits and emplacements.”

          Actually, it is 4 .50 cals (see the link; first version did indeed have only two MGs, but I fixed that in the revisal). And OLX’s primary purpose is two-fold: forward airborne observer for ALX and ground troops, and a COIN aircraft. In latter employment, main focus was on finding and engaging highly mobile, stealthy and lightly equipped enemy, so I never really gave thought to attacking fixed positions. In former, ALX will take care of fixed positions.

          https://defenseissues.wordpress.com/2014/08/16/forward-air-controller-aircraft-proposal-revised/

          “Dual BK-27 revolver cannon in each wing will allow it to really go to work against technicals, mortar pits and emplacements.”

          Agreed, albeit I don’t think they are necessary against technicals.

          “The other thing is sensors. If COIN/FAC craft are required to find opponents, then why skimp on the sensors?”

          Sensors won’t really help you find the types of opponents OLX is primarily aimed at. Best way to understand this are Platon’s “shadows”, here I will translate them to military context. If reality is a physical object, what we see when looking directly at the object is a shadow of it – an image descriptive of object, but at the same time removed from the reality of it. If it is too far, and we have to use a sensor, we are looking at shadow’s shadow. If we are looking directly, but have to find the object through indirect traces it leaves in surroundings – as is often the case in COIN operations – we are again looking at shadow’s shadow. If we use sensors to look at traces, we are looking at shadow of shadow’s shadow. And the usage of small displays means that even that ghost, already far removed from actual reality, is reduced, blurred – shadow’s shadow of a shadow’s shadow. Against a conventional enemy, it might not matter much. Against an enemy whose whole approach is based around stealth and subterfuge, these issues can be devastating.

          These links might explain the concept itself better (they are in Croatian, however):
          https://www.google.hr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj2wfDoitrLAhVGPhQKHWdeCh8QFggZMAA&url=http%3A%2F%2Fhrcak.srce.hr%2Ffile%2F65054&usg=AFQjCNGIutmO_YQikQYx4vHXyMPVwxhZxg&sig2=uLgSicULolgGVzASdFlGsQ&bvm=bv.117604692,d.d24

          Click to access 565946.Obradovic_Nemedijsko_zasnivanje_medijske_kulture_Mostar_110510.pdf

          Of course, FLIR and other thermals can be highly useful in some situations, but I see no need to equip whole fleet with them – night vision equipment for the pilot and observer would be cheaper and more intuitive to use (war is about people, not about equipment, so in some situations equipment that is superior on paper can actually be less effective). That being said, usage of DAS-like system would be a great advantage because it combines night vision capability with wide field of view on both sensor itself and on display – assuming that DAS works, of course.

          “A strong deterrent to mining roads simply did not exist despite extensive use of Predator drones with Hellfires.”

          Part of this was, I believe, because Predators flew very high and so could not notice the insurgents, limited as they were with straw-view sensors.

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       7. “Agreed. But AX is intended mostly for low-level CAS (aircrfat up high miss too much of what is happening due to straw view nature of sensors such as radar or FLIR), so I believe that standard night vision googles are appropriate for the most part. Another reason is that AX is a ground attack aircraft. Normal IRST is optimized for air-to-air role – mounted on the upper surface of nose, with either only LWIR or dual MWIR/LWIR channel. But a sensor for ground attack aircraft would have to be mounted on lower surface of nose and work in either MWIR or, preferably, dual SWIR/MWIR channel. You can see the issue right there – ideal location for sensor is also the only practical location for the gun. Mounting it on the upper surface is possible, but that restricts pilot’s view from the cockpit as well as sensor’s own view of the ground. So I really don’t see any option other than pod (or maybe integrated into a pylon or wing – but I don’t know any SWIR/MWIR sensor small enough for that).”

          Fair point on the IRST; which definitely works more as an A2A optimised sensor. About FLIR, we have much to learn from the application of such sensors in aircraft outside of the CAS or air superiority role – such as UAVs: http://21stcenturyasianarmsrace.com/2015/04/30/the-drone-index-sagem-patroller/ . A centerline, underslung ball turret that still yields enough space to the lower front nose for mounting of a gun.

          As an example, I call your attention to this cutaway drawing to the A-10: https://information2share.files.wordpress.com/2011/10/wallpaper-438762.jpg . At 46, behind the ventral gun bay access panels, along the centreline of the fuselage where the roots of the strakes are, one could place FLIR equipment. The alternative is to put it directly on the nose. The nose fairing at 2, and the space ordinarily occupied by the refuelling receptacle at 5 could mount the same equipment. Refuelling would then be handled by more conventional probe for probe and drogue refuelling offset from the nose; which also takes up less space, and is faster than flying boom, because more than one aircraft can be served by probe and drogue and a time.

          Nose mounted FLIR in the style of FLIR for helicopter gunships offers the maximum field of view for minimal drag imposition. It does have to be said, however, that sensors integration needs to be taken into account from the outset. In the case of the A-10, it would be difficult to justify re-engineering the nose assembly to incorporate it.

          “Sensors won’t really help you find the types of opponents OLX is primarily aimed at. Best way to understand this are Platon’s “shadows”, here I will translate them to military context. If reality is a physical object, what we see when looking directly at the object is a shadow of it – an image descriptive of object, but at the same time removed from the reality of it. If it is too far, and we have to use a sensor, we are looking at shadow’s shadow. If we are looking directly, but have to find the object through indirect traces it leaves in surroundings – as is often the case in COIN operations – we are again looking at shadow’s shadow. If we use sensors to look at traces, we are looking at shadow of shadow’s shadow.”

          These are fair points regarding narrow field of view sensors in general. I suppose we will have to wait and see regarding EO-DAS for the F-35; or invent IR equivalent to NVGs.

          I had a bit of a read of the POGO proposal for a next generation A-10: http://pogoarchives.org/straus/americas-defense-meltdown-2008.pdf (Page 160) . Surely an interesting proposal; as was reading about the Eliminator proposal done by San Luis Obispo students: https://ia600500.us.archive.org/15/items/nasa_techdoc_19920011633/19920011633.pdf .

          Listening to Sprey’s wishes for a new A-10 here: http://www.pogoarchives.org/straus/a-10/A10Conference_pt1_sprey.mp3 has also brought up some ideas.
          Condensed, they boil down to this:
          – Smaller, lighter electronics. We can do a lot more with electronics now than 30 years ago.
          – A better engine. Sprey considers the GE-100 as good enough at the A-10’s introduction but there are better engines now.
          – A smaller airframe. Sprey believes that the A-10 was a little larger than originally hoped for. A smaller airframe means better thrust to weight and faster, tighter turns for faster re-engagement
          – A better gun. Sprey actually thinks that the GAU-8 was a little too large and cumbersome with slow spin-up for the purpose.

          Addressed in turn:
          – Electronics are obvious. Given the A-10’s age, I wouldn’t be surprised to find old school stuff in there. A rebuild of the electronics using current components would no doubt cut down on weight and size.
          – Looking at the Eliminator proposal and at your choice of ALF-502 that was also used for the YA-9, have you considered the RB-199 104? https://en.wikipedia.org/wiki/Turbo-Union_RB199 . A better thrust to weight ratio and higher bypass ratio could mean a more sprightly climb rate.
          – Your proposal already has a smaller airframe. A slightly tapering planform, with increased trailing edge sweep would increase wing area though.
          – The issue is the better gun. Without a real successor CAS aircraft program, whose requirements are quite unique, we don’t have a lot to go on. A lighter, faster-spin-up gun by all accounts points to the G-Sh-6-30. The alternative would be a 3-4 barrel gas operated rotary or 5 chamber gas operated revolver firing 35x228mm at 1000-1200 RPM.

          The Eliminator proposed the use of canards and a redundant FBW system with an inherently unstable airframe. What are your thoughts on that? Personally, I would rather the plane be able to fly with half a wing on both sides cut off, half the tail assembly shot off and one engine out. That means electric with hydraulic backup. Canards sound interesting though. It would definitely shorten take off and landing.

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       8. “A centerline, underslung ball turret that still yields enough space to the lower front nose for mounting of a gun. ”

          Yes, that might work.

          “Nose mounted FLIR in the style of FLIR for helicopter gunships offers the maximum field of view for minimal drag imposition.”

          But gunship helos have externally mounted machine gun, doing so with a CAS aircraft is not an option.

          “These are fair points regarding narrow field of view sensors in general. I suppose we will have to wait and see regarding EO-DAS for the F-35; or invent IR equivalent to NVGs. ”

          It is far more than just narrow field of view; FoV is the biggest problem, but sensors are also typically monochrome, and in any case have lower resolution than human eye. This can make finding camouflaged targets difficult.

          “I had a bit of a read of the POGO proposal for a next generation A-10: http://pogoarchives.org/straus/americas-defense-meltdown-2008.pdf (Page 160) . ”

          Read it before, and I agree with all of it.

          “– Looking at the Eliminator proposal and at your choice of ALF-502 that was also used for the YA-9, have you considered the RB-199 104?”

          RB-199 has a too low bypass ratio for a subsonic low altitude aircraft.

          “The Eliminator proposed the use of canards and a redundant FBW system with an inherently unstable airframe. What are your thoughts on that?”

          FBW system and an unstable airframe are very bad ideas for a CAS fighter, while canards can be helpful if used in a statically stable design (higher maximum lift, stall recovery).

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       9. I still think that we need to design a gun from ground up for this purpose.

          What I’m thinking
          – Probably 35-40mm with a long barrel for high velocity.
          – We need to figure out how to get maximum ammo put down in the first 0.25 – 0.5s with a large calibre gun
          – Gun and ammo system should come with a feed for taking out different targets
          – One of these will be a tungsten sabot type of weapon that is designed for tank destruction, while others might be HE, incendiary, etc

          We could use 2x guns symmetrically placed or a gas operated gatling weapon.

          FBW system and an unstable airframe are very bad ideas for a CAS fighter, while canards can be helpful if used in a statically stable design (higher maximum lift, stall recovery).

          Yeah I would agree that FBW is not good – if you take damage, you could be in trouble to say the least.

          Maybe as suggested, an elliptical wing with canards (lifting) might be useful. I did notice that you got rid of the canards between the ALX v2 and v3.

          Personally, I’m still not decided on the number of engines a CAS aircraft should have.

          What would be the net thrust to drag ratio of a two engined CAS aircraft vs a single engined variant?

          On a separate note, if it ever takes off, I wonder if a Propfan might be a good compromise between a turbofan and a turboprop?

          <

          blockquote>
          Of course, FLIR and other thermals can be highly useful in some situations, but I see no need to equip whole fleet with them – night vision equipment for the pilot and observer would be cheaper and more intuitive to use (war is about people, not about equipment, so in some situations equipment that is superior on paper can actually be less effective). That being said, usage of DAS-like system would be a great advantage because it combines night vision capability with wide field of view on both sensor itself and on display – assuming that DAS works, of course.

          <

          blockquote>

          The main use I would guess would be to find enemy vehicles.

          That said, the heat from gun barrels that have fired might be something that can be located as well.

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       10. “I did notice that you got rid of the canards between the ALX v2 and v3. ”

           Due to engine placement. As I went back to having two engines, mounted on the wings, canards would have interfered with the air flow.

           “What would be the net thrust to drag ratio of a two engined CAS aircraft vs a single engined variant? ”

           It is more of an issue of survivability – smaller single-engined aircraft is more agile and so less likely to get hit, while twin-engined aircraft is more likely to survive damage.

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       11. Altandmain:

           “Maybe as suggested, an elliptical wing with canards (lifting) might be useful. I did notice that you got rid of the canards between the ALX v2 and v3. I did notice that you got rid of the canards between the ALX v2 and v3. ”

           Reading further, an elliptical wing is difficult to manufacture and repair. Given that this plane is going to be shot at, adverse repair characteristics are bad. A properly designed tapering or partially tapering planform can achieve almost the same (within 1-5%) aerodynamic efficiency-to-weight, while being much easier to repair and manufacture.

           “On a separate note, if it ever takes off, I wonder if a Propfan might be a good compromise between a turbofan and a turboprop?”

           I do not feel as though Propfans are sufficiently mature enough to be qualified for something like CAS. The Antonov An-70 mounting the Progress D-27: https://en.wikipedia.org/wiki/Progress_D-27 looks really promising, but the engine itself is quite oversized for the purpose. To use one means also taking on the risk of research and development of an engine.

           “I still think that we need to design a gun from ground up for this purpose.

           What I’m thinking
           – Probably 35-40mm with a long barrel for high velocity.
           – We need to figure out how to get maximum ammo put down in the first 0.25 – 0.5s with a large calibre gun
           – Gun and ammo system should come with a feed for taking out different targets
           – One of these will be a tungsten sabot type of weapon that is designed for tank destruction, while others might be HE, incendiary, etc

           We could use 2x guns symmetrically placed or a gas operated gatling weapon.”

           The problem with going to higher caliber is that even 5mm increase in caliber means that the mechanisms for loading, feeding, firing, extracting and ejecting have to be that much stronger, and that much heavier; to say nothing of the barrel or of structural reinforcement to handle recoil. The delta between the most powerful 30mm cartridge (30x173mm, muzzle energy 210000J from the GAU-8 firing PGU-13 ammunition) and the next caliber up (35x228mm, 1175ms muzzle velocity, projectile weight 535g = 379672J) is quite significant.

           https://en.wikipedia.org/wiki/GAU-8_Avenger
           https://en.wikipedia.org/wiki/Oerlikon_GDF

           The rounds are longer (173mm vs 228mm cartridge length) and heavier. This means that it will take a physically longer time to load and extract. It also impinges upon volume and mass when talking about carrying ammunition.

           I agree with you that going for 35mm is probably a good way to go. The problem is the weight: https://en.wikipedia.org/wiki/Rheinmetall_Oerlikon_Millennium_Gun . 450kg for a 4 chamber, 1000RPM revolver. Now it has to be said that it is a navalised version, which means bulkier, heavier stainless steels, and there is also extra weight to account for multiple munition feeds, and the fuze programming radar. But 450kg is simply way too heavy. The munition weight of 35x228mm at 1.535kg per round as opposed to 0.65kg for PGU-13/B is also a massive difference.

           Going to 35mm means adapting a ground-based gun and adapting the ammunition as well – the PGU-13/B series uses aluminium cases as opposed to brass or steel and uses plastic driving bands to save ~30% weight.

           Which is why I have my doubts that the proposed 35mm KCA revolver that Picard proposes for the AX heavy is feasible, and proposed the G-Sh-6-30 firing 30x165mm with improved higher pressure ammunition instead. More than 1500 rounds could potentially be carried, even before taking into account the possibility of aluminium cases and plastic driving bands; while increased barrel length from 1.8m (60 calibers) to 2.1 to 2.4m (70-80 calibers) could increase velocity without excessive weight increase.
           30x165mm Russian rounds are 850 grams as opposed to 630 grams of the PGU-13, but this is because they use steel cases, copper/steel driving bands, and electrical priming, which is heavier than fulminate priming. On the other hand, the rounds are much smaller, ammunition is cheaper, muzzle energy is better than the best Western A2A aircraft guns barring the GAU-8, and the guns firing it are mechanically simple and light.

           The prospect of a low spun weight gas operated revolver firing 35x228mm sounds great, but the problem is getting there. I don’t think that going for dual ammunition feeds or selectable drums is a very good idea for an aircraft gun though. The Oerlikon MG is testament to that. A single gun, with a high rate of fire, gas operated is the way to go.

           The question is: can we resurrect the Sperry Rand T249 Vigilante 35×228 6 barrel rotary?
           https://en.wikipedia.org/wiki/M247_Sergeant_York#Entrants
           – At what weight, length, size?
           – Using what cartridge loading, case, driving band?
           – Is 3000RPM 35×228 achievable with reasonable reliability and weight or should it be toned down? Land based platforms can afford a lot more weight than air based ones.

           Picard578:
           “Due to engine placement. As I went back to having two engines, mounted on the wings, canards would have interfered with the air flow.”

           Might it be better to follow the Eliminator’s cue and partially bury the engines in the fuselage? You can partially eliminate the weight of the cowling around the engine and reduce the structural load at the wing root since you can then thread bolts through to the main fuselage instead of having the wing take the whole weight. On the other hand, this puts the two engines closer together, which increases the risk of double engine damage. I would still rate it as a worthy tradeoff for aerodynamic reasons.

           This also permits the use of canards, as in the Eliminator. That said, aerodynamic modelling will be required to establish the degree to which the downwash from the canards inhibits airflow. Without evidence, I would intuit that it would not be that severe, because intake design matters more than the airflow around the forebody. The Eliminator went for a square design, but simple circle is also fine.

           The only thing I didn’t like about the Eliminator design was the insistence upon a low bypass afterburning engine (F404) which severely damages loiter time for marginal increases in cruise speed. However, the San Luis Obispo students terms of reference were for a “point defense” type of CAS aircraft with rapid turnaround time, minimal gun passes and focused more on rapid sortie rate and payload.

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       12. “On the other hand, this puts the two engines closer together, which increases the risk of double engine damage.”

           And that is the problem. Two engines close together don’t really bring any survivability benefits compared to a single larger engine.

           “The only thing I didn’t like about the Eliminator design was the insistence upon a low bypass afterburning engine (F404) which severely damages loiter time for marginal increases in cruise speed.”

           That is the second reason I want a podded engine. When buried inside the aircraft, engine has a major impact on body frontal area. This in turn has impact on both drag and on survivability (to survive a hit is good, to avoid being hit is better), and prevents usage of high-bypass engine, which is necessary for a CAS aircraft.

           Third reason is the ease of access for repairs. Granted, FLX would utilize a design akin to Gripen, which would make for an easy access, but engines outside the aircraft might still be better in that regard.

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       13. I think I’ve found an engine that could work:
           http://www.rolls-royce.com/products-and-services/defence-aerospace/products/uav/ae-3007.aspx#engine-specifications
           Or the successor to the ALF-507: https://en.wikipedia.org/wiki/Honeywell_LF_502

           A commercial engine that has also found its way into military use for UAVs, with application in high endurance aircraft. Offered with a range of outputs.

           Regarding the podded engines, they could either be put into the wing root or the fuselage. Podded onto the fuselage near the wing as with the LearJet series, I feel, would strike a good balance between separation, structural loading and probably exceed the serviceability of even the A-10, since the A-10 mounts it higher and to the rear while sacrificing in drag because the engines are angled slightly down for trim. Closer to the ground means easier to service, and mounting it closer to the center of gravity means less losses to trim. The higher thrust to weight ratio; albeit not by much, would also be assisted by lighter weight and greater maximum thrust.

           In LearJets, with more swept wings, the engines are mounted further back, which exposes the rear exhaust from the bottom aspect.
           However, in our design, without wing sweep or minimal sweep for a tapering planform, along with a trailing edge sweep to increase the wing root area, the wing itself could shield some degree of the exhaust; though the plume will still be present. The A-10 deals with that using a twin tail, but also loses out on drag due to engine trim.

           One thing I’ve been wanting to ask:
           Are pylons with fairings worth the weight at low speed in order to shield munitions from drag? I imagine a similar fairing type thing to the A-10’s wheel wells, but for bombs instead. Ditto for the wingtip station for defensive AAMs.

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       14. “Podded onto the fuselage near the wing as with the LearJet series, I feel, would strike a good balance between separation, structural loading and probably exceed the serviceability of even the A-10, since the A-10 mounts it higher and to the rear while sacrificing in drag because the engines are angled slightly down for trim. ”

           I had the same idea, but it would place engines too close to the fuel reserves (in fuselage and maybe the wings), and maybe increase the risk of FOD.

           “Closer to the ground means easier to service, and mounting it closer to the center of gravity means less losses to trim.”

           Closer to the ground means easier to service but also more vulnerable to FOD. Closer to the CoG means less losses to trim, but greater probability of fuel catching fire if fuel is also in the fuselage (and I don’t know where else to put sufficient quantity of fuel).

           “However, in our design, without wing sweep or minimal sweep for a tapering planform, along with a trailing edge sweep to increase the wing root area, the wing itself could shield some degree of the exhaust; though the plume will still be present.”

           I actually had an idea of engines podded right on top of the wing, close to the fuselage, where triangular wing extensions would shield both air intake from FOD and engine exhaust from the ground view, but I abandoned the idea – high risk of fuel catching the fire due to engines being too close.

           “Are pylons with fairings worth the weight at low speed in order to shield munitions from drag? I imagine a similar fairing type thing to the A-10’s wheel wells, but for bombs instead. Ditto for the wingtip station for defensive AAMs.”

           I don’t think it would help.

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       15. @MonMalthias
           Gsh-6-30 is an example of a gas operated gatling, btw. I’d be open to such a design, but I think the muzzle velocity needs to be improved – both with the pressure ammo and perhaps a longer barrel version as well. I’d be willing to sacrifice some barrel life for higher muzzle velocity.

           The only other alternative is to develop a custom gas operated gun or a custom higher caliber autocannon.

           @Picard,

           Maybe above the wing, but high above the wing? That would eliminate some of the serviceability advantages (although I suppose maintenance crews could stand on the wing to service), but if it was far enough, it should reduce the odds of catching fire.

           The only other way about this is to simply more heavily armor the engines.

           In regards to the single vs dual engine, I think that we are not going to know unless we ever get real world data. This is a classic chicken and egg problem – the probability of getting hit vs the probability of surviving a hit.

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       16. “However, in our design, without wing sweep or minimal sweep for a tapering planform, along with a trailing edge sweep to increase the wing root area, the wing itself could shield some degree of the exhaust; though the plume will still be present.”

           “I actually had an idea of engines podded right on top of the wing, close to the fuselage, where triangular wing extensions would shield both air intake from FOD and engine exhaust from the ground view, but I abandoned the idea – high risk of fuel catching the fire due to engines being too close.”

           I refer you to engine testing of a commercial engine (Rolls Royce Trent 1000) – https://youtu.be/VfomloUg2Gw?t=39m27s
           Explosive detachment of fan blade here: https://youtu.be/VfomloUg2Gw?t=40m44s

           Modern commercial engines are well designed enough to handle thrown blades. In military craft, I don’t think that the main threat will ever come from turbine failure – induced or otherwise, but from ground fire. That means armouring for threats from without, rather than from within.

           I’ve come around to mounting the engines above the wing directly on pylons. The spacing matters, yes, but as long as the engine pods do not directly abut the fuselage I think it will be fine. I would be more wary of fuel line fires than fuel tank fires; to be honest. It’s much harder to mount foam fire suppression on pipes and tubes than a monolithic tank. In addition, on-board gas generators like nitrogen separators can help inert the empty volume of depleted tanks. A leaking fuel line has no such luxury – and at altitude, the low vapour pressure of leaked fuel will volatilise and be likely ignited by the electrical components in the wing.

           I have here a report by NAVAIR on fire threats to aircraft: http://www.nist.gov/el/fire_research/upload/Chapter-2.pdf . Section 2.2.3 elaborates on what I am talking about. Dry bays carrying fuel lines are likely just as vulnerable, if not more so, than a self sealing fuel tank, properly inerted with OBIGGS. By the way, this is exactly what will kill the F-35 if hit now that they’ve stripped out fire protection for weight gains – if not lack of OBIGGS, then dry bay fires. The whole thing’s a $200 million tinderbox.

           For that reason I think that the engine pods should be mounted no further away from the fuselage than one engine width; and for the wing root to have armour covering the lines (fuel and electrical) out to the engine pods. Armour means weight, so ideally it should be used sparingly and for the design to accommodate that. Standard measures, like reticulated flame retardant foams, should not be ignored, but this is more basic engineering sense than additional survivability measures.

           Shorter fuel lines mean less dry bay vulnerability. A really wide wing root will help distribute the forces of an engine mounting, as well as giving space for landing gear. Tapering will help reduce the forces on the wingspan somewhat. The increased wing area at the wing root has other benefits – if the outer wing is shot off, you have more wing left.

           So overall your current design, aside from my quibbles about the wing, is pretty nice. This picture illustrates what I am trying to get at: http://www.artus-motor.com/uploads/pics/5554_1170786602_large_02.jpg . A nicely tapering wing, with trailing edge sweep that really expands the wing area beyond simple straight wing with tapered root. That the de Havilland Mosquito also just happens to be one of the more successful ground attackers is just coincidence, surely. Wet wing notwithstanding.

           Altandmain:
           “Gsh-6-30 is an example of a gas operated gatling, btw. I’d be open to such a design, but I think the muzzle velocity needs to be improved – both with the pressure ammo and perhaps a longer barrel version as well. I’d be willing to sacrifice some barrel life for higher muzzle velocity.

           The only other alternative is to develop a custom gas operated gun or a custom higher caliber autocannon.”

           There was such a Big Gun for trials way back when. As part of the Sergeant York SPAAG DIVADS system, several companies submitted high caliber rotary and revolver autocannon: https://en.wikipedia.org/wiki/M247_Sergeant_York#Entrants

           The one by Sperry Rand was interesting. 6 barrel Gatling, 35×228 Oerlikon KDA cartridge, 3000RPM. 1464 round magazine. No weight or volume given, although judging from the turret, not exactly light: http://www.quarryhs.co.uk/RED%20QUEEN.htm . Resurrecting the gun program might yield a useful gun. If it’s hydraulic powered, forget it. Too heavy.

           Which leaves us with a stripped down, souped up Oerlikon Millennium gun. Remove the fire control radar and dual ammunition feeds. It’s already gas operated, which is worrying, because firing at “only” 1000 RPM leaves the throw weight inferior. It may be that the dual feeds are slowing it down though; removing it may allow RPM to be increased. 2000RPM would be a nice target to reach. 35×228 from the top aspect could easily penetrate any MBT today, assuming they don’t have a lot of ERA. Lots of suppliers for ammunition, which helps with cost. Swapping brass for aluminium cases is essential if enough rounds are to be carried. Lighter ammunition will also increase rate of fire. Less inertia to slam around.

           Which brings me to this article here: http://nationalinterest.org/blog/the-buzz/mcsallys-case-lethal-next-gen-10-warthog-15064

           Clearly, we are not the only ones thinking about the next A-10. Thus far, the focus seems to be on defensive avionics – SPECTRA for Warthogs, if you will. The engines we’ve thought about. What’s most interesting was the cost caps that the pilots were emphasising – no more than $20 million CAPEX and $15000 per flight hour OPEX.

           Clearly, Hog drivers seem to be more fiscally responsible than those that oversee them. And we should be the same.

           That said, the devil is in the details. My wishlist:

           Engine: RR AE3007: https://en.wikipedia.org/wiki/Rolls-Royce_AE_3007 . A nice commercial engine, much snappier than the GE-100.
           Wings: Taper with trailing edge sweep like the DH Mosquito. Probably an even longer wing root extension for more wing area to distribute the load of an engine and hide the exhaust. Low wing, no wet areas, armoured fuel lines to the engines. Target of agility sufficient to have turning circle less than 1.5 km.
           Tail: Twin tail like the A-10. More control surface area. Also more to shoot off before control is lost.
           ? Canards ? More redundance, more better. Better short field performance. Better turn rate. But also increased complexity.
           Avionics: Ideally, SPECTRA, but the DAS on the Gripen would also work. FLIR to be mounted on a belly turret like surveillance UAVs, or we could have dual integral FLIR/targeting bays on the wings. Luxury item, but I would consider FLIR to be cheap enough now. A FLIR system with a wide angle view would be ideal for CAS at night, but EO with light amplification is also getting really advanced. The National Interest post mentions
           Armour: Engine pods, wing roots, rear fuselage, cockpit base (obviously), ammunition drum, fuel tanks.
           Seating: Single seat variant with less avionics, more ammo and payload. Dual seating variant with more avionics to double up as FAC with weapons and sensors operator (WSO); or as conversion trainer. Basically the same as A-10A and A-10 N/AW.
           FCS: Triple redundant. First line Fly by Wire, second line Hydraulics, third line pulley and cable. That means centre stick, but that’s not stopped anyone before.
           Gun: 35×228 stripped down Oerlikon Millennium gun with target of 2000RPM, 1000+ rounds. Given the ammo weight, that’s more gun passes than even the GAU-8, but it is less rounds down range. Belts should be mix of HEI-T and APDS.
           Fuel tanks: mid fuselage, armoured, inerted with OBIGGS, standard fire precautions. Target of 4-6 hours loiter at combat radius of 150-200 miles
           Landing gear: for rough field operations, just like those clever Soviets. If you can make a 25 ton Sukhoi rough field capable then there is no reason why the rest of the Western air fleet should not do the same.

           Cost: Picard says 9 million for an austere version. I think that with all the wishlisted avionics it would probably top out 12 million with OPEX around $10000 per flight hour.

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       17. “I’ve come around to mounting the engines above the wing directly on pylons. The spacing matters, yes, but as long as the engine pods do not directly abut the fuselage I think it will be fine. I would be more wary of fuel line fires than fuel tank fires; to be honest. It’s much harder to mount foam fire suppression on pipes and tubes than a monolithic tank. In addition, on-board gas generators like nitrogen separators can help inert the empty volume of depleted tanks. A leaking fuel line has no such luxury – and at altitude, the low vapour pressure of leaked fuel will volatilise and be likely ignited by the electrical components in the wing.”

           But feed to fuel lines can be closed in the case of engine fire. If engine is too close to fuel tanks, then it can ignite fuel in the tanks directly if hit ruptures both tanks and the engine.

           Of course, that assumes that fuel feed can be cut quickly enough.

           “For that reason I think that the engine pods should be mounted no further away from the fuselage than one engine width; and for the wing root to have armour covering the lines (fuel and electrical) out to the engine pods. ”

           Agreed.

           “So overall your current design, aside from my quibbles about the wing, is pretty nice.”

           I have issue with engine mounting. Current position places stresses directly on the wing, means that wing does not protect the engine from fire, whereas A-10s position (that I also considered) leads to maintenance issues because engine is high above the ground.

           “That the de Havilland Mosquito also just happens to be one of the more successful ground attackers is just coincidence, surely. ”

           Nowhere near coincidence, actually.

           “Clearly, Hog drivers seem to be more fiscally responsible than those that oversee them. And we should be the same. ”

           What is ironic is that both Hog drivers and USAF (br)ass care about the cost – but in opposite directions.

           “Target of agility sufficient to have turning circle less than 1.5 km.”

           Actually, search circle should be cca 400 m, from what I remember from the literature about CAS. I’m going to do a new proposal someday, so I’ll read about it again. Only question is when.

           “? Canards ? More redundance, more better. Better short field performance. Better turn rate. But also increased complexity.”

           Canards can be fixed, not necessarily mobile. But they cause increased drag during level flight, ergo lower loiter time.

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       18. The fuel lines need a way to stop the fuel feed quickly in the event of an emergency.

           Perhaps the fuel feed to the engine should be somewhat armored (yeah it will add some weight, but I think the survivability may be worth looking at, especially for protection against shrapnel or hits in critical locations).

           I’m not convinced about wing – I think that we may be forced to go with fuselage.

           We want:
           1. Engine to be moderately far from fuselage to prevent fires, but not too high as to minimize maintenance difficulties
           2. Engine to be close to the centre to maximize efficiency, but not too close as to minimize the risk of any hits to a single engine spreading
           3. An alternative is Picard’s single engine variant – we may want to go back to something closer to the v2 (https://defenseissues.wordpress.com/2013/12/07/close-air-support-fighter-proposal-revised/)

           @MonMalthias
           I don’t think that the US ever developed a major gas operated gatling weapon.

           As I’ve said before, I think thought that the big moral we should take from gatling weapons though is that if we want a good CAS aircraft, we will need to design a custom gun for it, and like the A10 build an airframe around that gun.

           For your wishlist, one question must be the materials choices for the armor. It could be a titanium – composite type, but the cockpit must be very heavily armored. So too must be the canopy.

           What are your thoughts on bicycle landing gear? I was reading this old report when Pierre Sprey had Hans Ulrich Rudel interviewed:
           http://www.allworldwars.com/Proceedings-of-Seminar-on-Air-Antitank-Warfare.html

           If we are going to be serious about a grass-field capability, and I know as painful as it is to pilots who have grown up with tricycle landing gear, tricycle landing gear just is not adequate for landing in a grass field. There are years and years of pre-World War II experience, there are years of crop-duster experience that show that if you are going to land on a grass field, a bicycle landing gear, two wheels, is the only way to go.

           On the note of tanks and IR missiles, I wonder if flare dispensers might work with tanks to defend themselves? Especially for IR missiles. Maybe some chaff too. Smoke to scatter laser guided missiles, flare for IR, chaff maybe as well, and if that fails, something like the Israeli Trophy may be worth a look at. Finally, explosive reactive armor (dual layer to defeat dud projectiles).

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30. Also worth looking at for rough field operations – tundra tires (all models proposed here):

    https://en.wikipedia.org/wiki/Tundra_tire

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    1. @Altandmain
       “What are your thoughts on bicycle landing gear? I was reading this old report when Pierre Sprey had Hans Ulrich Rudel interviewed:
       http://www.allworldwars.com/Proceedings-of-Seminar-on-Air-Antitank-Warfare.html”

       “Also worth looking at for rough field operations – tundra tires”
       Tundra tyres are basically half-flat tyres. If you’ve ever had a flat tire on your car and tried to drive on it, you would somewhat replicate the handling of a tundra tyre.

       There are many ways to do landing gear. Of all of the arrangements, only the tricycle landing gear arrangement has come to really dominate.
       https://en.wikipedia.org/wiki/Landing_gear
       There’s a few reasons for this.
       – A tricycle landing gear arrangement distributes the load relatively evenly
       – There is no need for outriggers (see Bicycle landing gear of Harrier Jump Jet and outriggers on wings)
       – It is inherently stable. Rear skids are inherently unstable; and bicycle gear requires the weight and drag of outriggers, or really balanced craft (i.e. no external stores). In Rudel’s time of piston props, attack aircraft were dominated by their cannon; stores could be jettisoned for easier landings, and there were no targeting pods on pylons that cost your average luxury car. If the outriggers don’t deploy, ditching your hundred thousand dollar targeting pod would be somewhat frowned upon. Better than a lost airframe, but nevertheless expensive.
       – Placement is easier with more options. Forward placed central gear leg retracts into front fuselage and gives good over the nose visibility. Taildragger central gear leg is important for propeller driven planes and makes it more idiot proof against tailstrikes.

       In terms of what goes onto the bogies, the most practical for combat aircraft is that already used by aircraft like the A-10, the SEPECAT Jaguar, and the MiG-29: simple tyres. Big ones, to be sure, but skis and skids are inherently unstable and cannot be steered while tracked bogies are too heavy and bulky. Here is a video of the SEPECAT Jaguar rolling on unprepared ground: https://youtu.be/z-uqMUA7U-k?t=1m34s . As you can see, despite the bouncing, even a single front wheel gear on oleo struts is sufficient for rough field operations. In this case, rough as in an unprepared grass strip.

       Keep it simple. Copy the front landing gear of the MiG-29 and the partially retracted main gear of the A-10 into fairings and leave it at that. Properly designed, you will get a plane that can be rough field capable; better than the A-10, and perhaps even better than the SEPECAT Jaguar. http://s4.photobucket.com/user/joselu/media/DSC07779.jpg.html . Recall that the A-10, being designed around the gun, has a relatively anaemic front landing gear that precludes it from truly rough field operations (although compacted dirt strips would work), but due to its efficient engines, has the range and loiter to compensate. A truly army-integrated CAS aircraft, fighting with the front line, moving with the front line, will not have that luxury. You can also elect to have longer landing gear with longer, stronger shocks, but this has a space and weight penalty. A tapering planform with trailing edge sweep gives us the room to have quite long landing gear though. Setting the wing low also improves access to stores.

       By far the most important factor, however, is in the attention to detail. What allows the MiG-29 to be rough field capable, beyond its strong landing gear, is the simple things. Mud guards: http://hsfeatures.com/images/mig29fm_3.jpg . It is what allows the designers to avoid excessively long landing gear like the Jaguar while having low set intakes with landing gear in front of them. Granted, the MiG also had retractable FOD screens for the intakes, just in case.

       In a design that mounts the engines above the wing, longer landing gear is not necessary; only strong landing gear. Big wheels and good shocks are all that will be needed.

       For gun considerations, the front landing gear would have to retract backward if two wheel front gear are to be used. A taildragging arrangement, on the other hand; would have no such restrictions. The question then becomes what to do with the empennage and how long to make the tail gear – how much of a nose up attitude can one tolerate before visibility becomes too low?

       All of the above is made a lot simpler, if we elect to restrict ourselves in certain ways:
       – The overall airframe size should be somewhat less than that of the A-10. Probably with overall length of no more than 14-15 meters.
       – The wingspan can be shortened using a tapered planform with a trailing edge sweep. Wingspan of no more than 15-16 meters, if not less.
       – Fully loaded weight of no more than 18000-20000kg. A fully loaded A-10A is ~22000kg in comparison.
       – This means that the same landing gear can tolerate a greater bring-back capacity, and rougher fields.

       The Air Force fought, and won, the battle to make the A-10 carry an enormous load. STOL capability, Thrust to weight and agility were heavily damaged.

       Going back to the gun, this table by Anthony Williams on the RMK series of recoilless revolver cannon is interesting:
       http://www.quarryhs.co.uk/RMKtable.jpg for ammunition and gun weight
       http://www.quarryhs.co.uk/RMKchart.jpg for muzzle energies. RMK35/1 firing 35x300mm develops ~315000J – more than 30x173mm at 210000J, but less than 35x228mm NATO at ~410000J. As a recoilless gun, most of the energy is lost going out the back of the venturi. However! Look at the gun weight: 152kg. Ammunition weight of only 900g per round (it’s caseless electrically primed). That’s

       Now, rate of fire would have to be increased from 300RPM to 2000RPM. There are only 3 revolver chambers – this would have to be increased to around 5-6 chambers due to concerns about cook-off. A heavier, stronger electric motor will be required. Most likely, there will need to be a bulged fairing along the bottom of the nose to accommodate the venturi and the underside of the nose dampened against backblast. However, the reduced recoil impulse means less internal bracing, and the gun itself would be likely be far lighter than a souped up Oerlikon KDG Millenium Gun.

       Ultimately, the engineering challenges may prove too great, and we will be using the KDG instead. At that point, refactoring the ammunition into aluminium cases and plastic driving bands would most definitely be needed to reduce per-round weight to manageable levels (1kg per round should be the goal)

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    2. Thinking more on the RMK30 or RMK35/1, the allure of low weight, low recoil, high muzzle energy and low ammunition mass (comparatively to 35x228mm) is too great to ignore. That said, having a recoilless design means several engineering restrictions:
       – Having to take into account gun gas ingestion for the engines. This is especially bad for recoilless designs as most of the gun gas goes out the back instead of out the front. The A-10 countered this by having combusters turn on when the gun was triggered. However, we are talking a lot greater volume of gun gas, expelled to the rear, with little opportunity to mix with surrounding air. Some of this might be countered by mounting the guns low in the nose; perhaps even to the point that there are blisters coming out the bottom corners of the fuselage.
       – A recoilless design incorporating venturi precludes easy engineering for gas operation. That means heavy electric motors and impinges on the aircraft’s electric grid for electrically driven operation. On the other hand electrically driven operation means fully positive control of extraction and ejection, and the only theoretical limits to firing rate are the power of the motors, and barrel and chamber heating.
       – The venturi is especially complex for a nose mounted gun. The RMK30 series mounts the venturi right out the back of the firing chamber for obvious reasons. In an aircraft, this would mean mounting the gun low with the venturi out of line of the fuselage and a blister fairing open at the back. This is probably draggy.
       – Another solution to the problem of low firing rate of the RMK series is double the gun. There are a few benefits to this. For one, it reduces the amount of re-engineering required to increase firing rate to acceptable levels. It introduces redundancy in the case of jam (although electrically driven guns are quite reliable). It also allows us the luxury of using 2 feeds as Pierre Sprey advocated for, without the mechanical complexity of dual feeds. Mount the drums in tandem (to avoid lateral centre of gravity changes as ammo depletes). The penalty is weight. 1 RMK35/1 is 152kg. 2 is 304kg. Now, there is no weight penalty of internal bracing because the guns themselves do not have a powerful recoil force, so how much weight is saved there? However, it has to be said that engineering the RMK35/1 for higher rate of fire would also increase the weight. A mere 50kg increase per gun already puts us on par weight wise with the Oerlikon KDG.
       – Of course, we could also leave the firing rate as is. 600RPM is still 10 rounds per second; and perhaps a tight search radius with a swift time for re-attack is better. 35×300 is also flatter shooting, which means a greater engagement range, so that extends the firing time somewhat. The RMK series is apparently quite accurate as well – although better accuracy means needing better pilots too.
       – 2 guns side by side also has another benefit: front mounted landing gear. The Mirage III had 2 DEFA (later GIAT 30) cannons firing from ports to each side of the nose. This left lots of room for the radar and landing gear. We can do the same with 2xRMK 30 on each side of the nose. This now leaves the nose fairing free for aerial refuelling probes, FLIR, whatever. It means the nose can be made shorter, for better over the nose visibility, which is important for landings and strafing runs. It also means we do not have to have an anaemic front central gear leg. As a recoilless gun, there are minimised lateral recoil forces, even if only 1 gun is firing (for select feed reasons, or if 1 gun is jammed). I doubt that even with a blocked venturi that there will be significant induced yaw. In addition, servicing the guns is much easier as technicians could access them through armoured panels on the side of the fuselage; as opposed to having to crawl beneath the A-10 and work from underneath.

       Another thing about the design is that the A-10 surprisingly has wet wings; right at the wing root, extending all the way out to the landing gear fairings. If we follow Fairchild, this may partially alleviate the problems of fuel capacity: https://information2share.files.wordpress.com/2011/10/wallpaper-438762.jpg . The engines are also mounted to the fuselage just as the fuel tanks end. Fairchild Republic likely felt that short fuel lines could be traded off against fuel proximity to engine. In addition, after the engines there is essentially empty space in the empennage barring the usual RWRs and tail lights and such. Most likely, the rear mounting of the engines left the balance of the aircraft such that the use of the empennage for anything was quite restricted.

       The second surprising use of space is in the avionics. There is a lot of space for it just behind the cockpit; while leaving the nose fairing relatively sparse. By far the most surprising is the ammunition handling system and drum – that space ends just as the fuel tanks begin. All around it are squeezed more avionics. Ammo and fuel next to each other, without firewalls, with lots of potentially sparking electronics right next to a big fuel tank. I guess when Sprey emphasised never to put engines and fuel together he forgot to also mention never to put ammo and fuel together. Now, to be fair, Fairchild was kind of forced to do so due to the sheer length of the gun and ammo system; and the ammo drum is armoured. At 6.06m overall including the drum and feeds, the GAU-8 is troublesome to fit into something as difficult as an airframe. We will have the same difficulty cramming the KDG in there, if not more so.

       If we were to move to 35x228mm or 35x300mm caseless, we would also have a longer gun length to contend with: 2.85m for GAU-8 and 3.2m for RMK35/1 and a gratuitous 4.11m for the Oerlikon KDG alone: http://warfaretech.blogspot.com/2014/03/oerlikon-35mm-cannon.html .

       These changes mean that in all, our center of gravity is likely shifting towards the middle of the aircraft. This means that we are more free to have fuel tanks extending further into the empennage space. In order to keep the engines away from the fuel, the avionics bays can be shifted from behind the cockpit to the centre of the craft, separated on both sides by firewalls and fire suppression equipment. Access to them is from below. In addition, since a lot of space has been cleared out around the nose, more area could also be used there for avionics. Other spaces would include the landing gear fairings; since the extended wing root also deepens the fairing; more equipment could be mounted there if truly necessary; while leaving servicing simple since technicians can access them from above or below the wing. That being said, if even all this is not enough, the thick wings and to some degree the empennage can be used; though the space in the empennage would be better served as space for flares and decoys. There is some “play” possible in this design since thus far we have avoided wet wings. Going for wet wings or avionics in the wing roots is also an option.

       Taking all of this into account, here’s an alternate vision for the A-X:

       View post on imgur.com

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       1. Recoilless gun might work better as an external application. You could mount several under the wings (some actually did that during WWII) and it would not cause problems with gas ingestion etc.

          “It means the nose can be made shorter, for better over the nose visibility, which is important for landings and strafing runs.”

          Check my earlier ALX proposals. Gun actually has no impact on nose length because it is mounted far back – ammo drums are around center of weight, if I recall.

          “By far the most surprising is the ammunition handling system and drum – that space ends just as the fuel tanks begin.”

          Yes, my ALX has the same problem, although fuel and ammo are separated by an armored bulkhead. That being said, if the ammo cooks off, pilot is dead due to being hit by bullets (granted, there’s also armor between ammo bay and the cockpit, but I’m not sure it would be enough.

          “These changes mean that in all, our center of gravity is likely shifting towards the middle of the aircraft. This means that we are more free to have fuel tanks extending further into the empennage space.”

          I actually had an idea, due to the 35 mm’s rather generous size, to mount ammo drum at the rear end of the aircraft, and gun below the fuel tanks. Avionics bays can be mounted between the ammo drum/feed bay and fuel tanks, as well as between fuel tanks and cockpit.

          “Taking all of this into account, here’s an alternate vision for the A-X:”

          Looks fine, albeit I opted for refuelling via boom for most of my designs so far.

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       2. “Recoilless gun might work better as an external application. You could mount several under the wings (some actually did that during WWII) and it would not cause problems with gas ingestion etc.
          I actually had an idea, due to the 35 mm’s rather generous size, to mount ammo drum at the rear end of the aircraft, and gun below the fuel tanks. Avionics bays can be mounted between the ammo drum/feed bay and fuel tanks, as well as between fuel tanks and cockpit.”

          Here’s an iteration close to your vision then:

          View post on imgur.com

          I’m a bit iffy on wing mounted guns due to convergence issues. For strafing it might not matter so much but then you have the issue of feeding the guns with wing root ammo bays; or long linkless feeds to the fuselage. Doable, but probably difficult to service in the case of a fuselage drum, and limited ammo capacity in the case of wing storage. Now, a tapered wing has much more area, but these are very large rounds compared to the 20mm Hispano ammo in days of yore.

          It also extends vulnerability since a rear fuselage drum will have to squeeze feeds past fuel tanks. Today’s ammo is much less sensitive, but still flammable. Caseless ammo moreso. That said, if we are still using the KDG then it would be possible. In fact it would allow for a forward retracting landing gear, which is stronger on landing; and the retracted front gear also ballasts the rear bias of weight.

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    3. Interesting thoughts.

       If a recoil-less design is used, I wonder if there is a way to redirect the gun exhaust somehow. I was thinking about some sort of a vent to try to get the ammo to not hit the engine intakes with low oxygen exhaust. The problem is how to get that to happen, while keeping the desirable recoil-less properties.

       I wonder if the guns could be made further to the rear (ex: right below the wing root). If the engines are mounted on the wing or on the fuselage, then it might also be able to avert the worst of the gun exhaust too if the guns are mounted low. Then the avionics bay would be right behind the seat, while the ammo would be between the two fuel tanks – the problem though is that as you note shielding, but it may be worth it. Hmm … it may be impossible to determine without real world testing.

       Another challenge could be to try to get the longer bullet in 35×350 gun, while keeping the multiple chamber design of the slower weapons to try to sustain the rate of fire, while keeping the weight down. Barrel life will be short of course.

       Where do you propose putting the electric motors? They have to be in a place that is resistant to damage so that if the aircraft takes a few hits (expected) the guns still work. I have wondered if the benefits of recoil-less could somehow be combined with using some of the recoil, the gas impulse to physically reload the gun, thereby doing away with the need for a motor? Hmm … maybe impossible.

       On the other hand, may very well be that something like the Gsh-6-30 is the way to go, or at least with a higher muzzle velocity. I wonder what a longer barreled hypothetical Gsh-6-35 would be like – especially if it could combine it will the caseless electrically primed ammunition. Hmm … we won’t know until we get real world testing. The problem is that most armies don’t value CAS.

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       1. The problem as I see it with mounting the guns so far to the rear or on the wing roots is convergence. The most accurate and reliable way to mount any weapon on any platform is rigidly; and centered. As you move away from centerline you will have increasing issues with accuracy. See the A-16 gunpod.

          Now, a belly blister, with rear venting for the venturis can work. The Hawker Harrier did it for years with its ADEN gunpod: http://imagery.vnfawing.com/archive/Weapons/AIM-9/p0001919.jpg

          But look at how much it sacrifices: in drag, in ground clearance. The only reason it works is because it is VTOL and therefore has less concerns with rough field performance. In belly-up landing, what will probably happen is an ammo explosion and a loss of the airframe. I am already risking this with corner placement; however, placement on the forebody is less risky since there is the partially retracted landing gear to take the worst of the shock and the impact is well isolated. Placing it in a belly blister would also work, but also sets minimum clearances; the blister would have to be less protruding than the main wheels or it too will take the worst of the shock. If we also assume the worst case and the wheels blow from the pressure of a crash and we are left with hubs only, that leaves even less clearance.

          Moving the guns towards the bottom of the fuselage negates the serviceability advantage, as well as limiting front landing gear size, while increasing drag since we need more clearance. The front landing gear with a long oleo strut with a single, large wheel as per SEPECAT Jaguar could work – however, the Jaguar has a 15700kg max takeoff weight.

          The A-X is probably closer to 17000kg if we insist on bigger guns (2x152kg = 304kg, + 1000x900g = 900+304kg = 1204kg minimum. The GAU-8/A has a system weight of 1,828 kg due to drum weight, linkless feeds etc. I sincerely doubt that we can do better with heavier guns (+23kg minimum for difference in guns), and heavier ammo (900-764kg=+136kg extra for ammo). The obvious sacrifice is in payload and range.

          We probably could achieve 15000kg max takeoff, but only if we then allow ourselves to use composites; and that means cost. Personally, I would favour complete construction out of Al-Li; for repairability and for cost. That being said, the A-X is much, much smaller; so we will have to see.

          “Where do you propose putting the electric motors? They have to be in a place that is resistant to damage so that if the aircraft takes a few hits (expected) the guns still work.”
          In the RMK30, the motors are integral with the gun: http://www.whq-forum.de/cms/246.0.html . Actuation is by cams on the cylinder surface.
          
          https://www.google.com/patents/EP1843120A1?cl=en&dq=ininventor:%22Hubert+Schneider%22&hl=en&sa=X&ved=0ahUKEwjChICuh_LLAhWn26YKHaT5BAMQ6AEIWTAI
          The whole mount is surprisingly compact. Here is the thing mounted on top of a Wiesel light tank: http://www.combatreform.org/wiesel1withRMK30mmautocannon.jpg
          Here it is firing: http://28.media.tumblr.com/tumblr_lnpzpgB0CA1qlcxqlo1_500.jpg

          As I mentioned though, the engineering complexities might make it simpler to just use the KDG instead.

          “If a recoil-less design is used, I wonder if there is a way to redirect the gun exhaust somehow. I was thinking about some sort of a vent to try to get the ammo to not hit the engine intakes with low oxygen exhaust. The problem is how to get that to happen, while keeping the desirable recoil-less properties.”

          The Luftwaffe experimented with the Mk115 5.5cm aircraft gun that was recoil-less.
          http://www.ww2incolor.com/forum/showthread.php/4127-Luftwaffe-Cannons-amp-Machineguns/page14
          Their solution was to have a gas port tapped off the firing chamber that was opened once the mechanism had recoiled sufficiently and the cartridge was partially withdrawn. This will not work with a caseless round – there is no cartridge to seal. In addition, the cartridge itself was low velocity in order to prevent excessive gas pressure eroding the tight tolerances. Overall a highly complex mechanism susceptible to wear, however, it does demonstrate the ability to redirect gun exhaust.
          One of the reasons why recoilless guns are the way they are is because for recoil mitigation, you need the escaping gas to be of a very high velocity in order to counterbalance the reaction force of the accelerating round. That is why the venturi is often mated directly to the firing chamber. I think the proportion is 4 times the mass flow of gas to projectile. Venturi that are eroded, or that are far away from the firing chamber, do not allow the gas to escape as efficiently or as fast. That is why worn out recoil-less rifles begin to “gain” recoil. At some point, you are better off in terms of weight, to simply have a sealed chamber cartridge and hydraulic shock absorption. I don’t know the exact mathematics behind it; but suffice it to say that redirecting the exhaust is non trivial.

          In any case, having blisters for venturi is a worthy tradeoff in the increase in firepower for relatively low sacrifice in extra weight; and in fact, there is more total potential muzzle energy in this than even the A-10.
          The GAU-8/A firing the PGU-13 HEI round develops 210000J. Total rounds carried: 1174. Total 246.54MJ. Weight: 764kg
          The RMK35/1 firing 35x300mm caseless RCL develops 315000J. Total proposed rounds carried: 1000. Total 315MJ. Weight: 900kg

          With such a disparity it may even be that aiming for 1000 rounds is too much. In fact if we only carry 800 rounds we would still get total potential muzzle energy of 252MJ, ammo weight would be 720kg. Less ammo means lighter ammo drum, smaller space, etc. Every kilo saved means a shorter takeoff run, less ground pressure, and greater endurance.

          Let’s take the GAU-8/A system weight: 1828kg. With 764kg ammo and 281kg gun, the drum and ammo handling is 783kg. Let’s also assume that the drum and ammo handling for the 2xRMK35/1 is the same. More likely, it will be heavier due to longer and wider linkless feeds, larger drum circumference due to longer rounds, etc.
          2xRMK35/1 = 152×2 = 304kg
          Add 783kg drum = 1087kg.
          Add 1000 rounds ammunition = 1087kg + 900kg = 1987kg. 159kg heavier. To equal the GAU-8/A system in weight we would have to remove 159 / 0.9 rounds = 177 rounds of ammo. So 823 rounds of ammo could be carried before weight increase. Keep in mind that this figure does not take into account the weight of the blisters; however, we are assuming that the blisters are made to be part of the spaceframe or monocoque construction and thus contribute to the weight-bearing structure instead of adding to it.

          @Picard578
          “I actually had an idea, due to the 35 mm’s rather generous size, to mount ammo drum at the rear end of the aircraft, and gun below the fuel tanks. Avionics bays can be mounted between the ammo drum/feed bay and fuel tanks, as well as between fuel tanks and cockpit.”
          That might make the thing tail heavy. Without CAD, it remains to be seen.

          Moving the guns further back does have merit, as it centralises weight distribution and frees up space for front landing gear. But it also means that we will have to put the guns in blisters beneath the forebody; and it means blast tubes if we want them integral, or a fairing if we don’t mind the bumpiness. Use of taildragging landing gear makes things a little easier, but not by much; and probably worsens effect on balance as now your ammo drum is probably behind the centre point.

          The prospect of having a fuel tank behind the cockpit, behind a firewall does have merit; though it would mean having linkless feed extend right past fuel tank to guns beneath or having the guns in the belly. Again, I’m a little iffy on that; but certainly it has its own tradeoffs; and for sure it would require much larger wheels or lower set fairings or both, to assure clearance in the event of belly-up.

          Putting avionics bays behind cockpit then having the ammo drum there does have its merit as then we can have a single bulkhead separating fuel from ammo. It does leave the potential for uneven weight distribution since the fuel is entirely drawn from the rear half of the aircraft. The wings and engines would therefore need to be moved back; unless we are happy for pilots to fly trimmed on their way back from missions.

          I don’t think there’s any one right answer. The closest we can come to verification is to build it; or the equivalent in a CAD program.

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       2. “That might make the thing tail heavy. Without CAD, it remains to be seen. ”

          If it ends up tail heavy, it means placing both wings and wing wheels further back, and steering wheel stays at the nose.

          “Moving the guns further back does have merit, as it centralises weight distribution and frees up space for front landing gear. But it also means that we will have to put the guns in blisters beneath the forebody; and it means blast tubes if we want them integral, or a fairing if we don’t mind the bumpiness. Use of taildragging landing gear makes things a little easier, but not by much; and probably worsens effect on balance as now your ammo drum is probably behind the centre point. ”

          Ammo and fuel are not being expended at the same rate, balance would shift no matter the arrangement (unless ammo drum is directly at the C(g)), and you have to account for fuel tanks ruptures etc..

          “Putting avionics bays behind cockpit then having the ammo drum there does have its merit as then we can have a single bulkhead separating fuel from ammo. It does leave the potential for uneven weight distribution since the fuel is entirely drawn from the rear half of the aircraft. The wings and engines would therefore need to be moved back; unless we are happy for pilots to fly trimmed on their way back from missions. ”

          At least wings can be placed nearly anywhere (and I do mean nearly anywhere, just look at all designs). If C(g) is shifted rear, wings move back, what is important is that it doesn’t shift too much during the flight. Which means that fuel should be around the C(g) of an empty aircraft.

          “I don’t think there’s any one right answer. The closest we can come to verification is to build it; or the equivalent in a CAD program.”

          Agreed.

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31. I think that we will need a CAD model to see.

    In practice, if this were the real thing, we’d likely have a fly-off kind of like YF-16 vs YF-17. The defense reformers always advocated for that for a reason. I suspect that just like the YF-16 proved superior, we’d see one design become superior.

    Actually, it would not be just one fly-off; several configurations would be tested:
    – Single vs dual engine
    – The rear heavy vs front heavy
    – During prototyping, we’d want to see the ability of the aircraft to be maintenance and repaired
    – How well it can take damage will of course need to be tested

    Another question might become bursts. The first 0.5s is of course critical and the shots between 0.5s and 1s are far less potent. After 1s is not that useful. One question I do have becomes how many fractions of a second is optimal, giving a good balance between Pk and the number of trigger pulls. Perhaps the maximum number of kills per sortie is the desired result. The pilot should be able to choose that.

    @MonMalthias

    I’d say that the RMK35 has enough advantages to be worth exploring.

    Hmm, perhaps the 2x RMK35/1 may be the optimal choice. I suspect that an A-10 mass of aircraft might be able to take the 35x350mm with something closer to the RMK35/2 as I suggested, at the expense of mass.

    I’ve always leaned towards 3 aircraft myself:
    1. An OLX
    2. An ALX (like this one)
    3. A dedicated tank killer, which will be a bit bigger and heavier, but able to kill a modern 70 ton tank outright (not just mission kill)

    One concern that I do have right now with caseless ammo is that it tends to not withstand the elements very well and we are sending this CAS aircraft into places where it will be exposed to elements. This could lead to “cooking off” of ammo or fragments getting stuck in the barrel (a maintenance nightmare). I wonder if cased telescopic ammunition or something similar could be an option.

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32. @Altandmain:
    In all, this discussion may be moot. Rheinmetall chose to discontinue the project, after there was no official interest in the weapon. Meanwhile, the Oerlikon 35/1000 KDG is extant. The ammo and gun weight is much heavier, but the gain in muzzle velocity is arguably worth it. For a system weight equalling the A-10’s at 1828kg, and assuming drum and ammo handling is equivalent (unlikely given the larger size), then this leaves 1828 – 450kg (gun) – 783kg (drum + ammo handling) = 595kg ammo. At ammo weight of 1.535kg per round of 35×228 ammo, that leaves only 387 rounds.

    Obviously, a bigger gun means a lot less ammo. Aluminium casing is a must. At a nearly 4:1 density ratio: http://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html there could be significant gains in ammunition capacity. Arbitrarily, I would try to cram in around 1000 rounds, even at the cost of payload for other things; nothing beats a gun for reliable close support.

    Something that has come to my attention recently is the Textron/Cessna AirLand Scorpion: https://en.wikipedia.org/wiki/Textron_AirLand_Scorpion and https://www.youtube.com/watch?v=7yY0yEtxt-Q . Textron has done what few would imagine; producing a trainer that has inherent qualities for ISR / FAC and light attack. 4-6 hour loiter time with commercial engines, commercial hydraulics and commercial electronics. Manual backup in case of hydraulic failure. Twin engine, twin tail design. That said, the design uses a high wing with LERX and underslung engines, which is not ideal for ground crews. The choice of high wing also forces fuselage mounted, narrow track main landing gear, which impinges on fuselage usable volume. The front landing gear are similarly anaemic. Definitely not a rough field performer; however, its supremely light weight and good thrust to weight doubtless make it perform well enough on a runway.

    The showstopper is Textron’s choice of a Composite airframe with 20000 hours of life. The unit cost is therefore around 20 million for what would otherwise be an exceptional aircraft. As a trainer that would build up lots of hours, I can see where Textron is coming from; however, that alone jacks up the CAPEX to unacceptable levels.

    That said. The reason why I bring the Scorpion up is not to excoriate Textron for their engineering choices, but in their very clever design.

    Textron chose to have a slightly wider body so as to be able to engineer in a belly bay. In the Stratpost video, the test pilot makes much mention of the belly bay for mounting turreted surveillance avionics or whatever the customer preferred. The bay has 1400kg capacity for munitions (volume unspecified).

    This brings me back to Picard’s alternate proposal with belly mounted cannon; that I later iterated on.

    Based on Textron’s design choice, and the Picard’s alternate proposal, I can definitely see a possibility for a common airframe emerging, built around a centered belly bay.

    The basic vision is an airframe built around the Oerlikon KDG mounted in a belly bay of 2500kg capacity. That sets the minimum standards of structural strength and reinforcement required of a useful mounted gun. It also means that our front landing gear can be as massive as we want it to be, fold forward on closing with ample room, and be as robust as required for rough field operations; while being largely free in terms of cockpit design since there is no ammo drum behind the cockpit. A 2500kg bay with 450kg gun and 783kg drum yields 1267kg ammo. Assuming brass cases, this leaves 825 rounds worth. Assuming 25% ammo weight reduction (highly conservative given ammo weight reductions achieved by PGU-13 series) this leaves 1032 rounds – enough for a full minute of fire at 1000RPM. That’s a lot of gun passes; however, the KDG is inherently more accurate than the GAU-8 while each individual round is much more deadly than 30x173mm; in terms of muzzle energy and in terms of explosive weight. Though thrown weight matters, accuracy, armour penetration and explosive load per projectile matter in ways that make a simple thrown weight calculation deceptive.

    A variant can be built around the same airframe, that removes the gun mount, and mounts ISR avionics on it. This serves the FAC role. The empty space could be taken up by more fuel for greater endurance.

    Or it strips everything for a basic trainer. No armour, minimal avionics. This is what a company sells in lean times and gains the most service contracts for.

    In all cases the basic variant would incorporate a tandem cockpit; though a single cockpit would also allow for greater fuel capacity, FAC and CAS impose a relatively high pilot workload with high chance of tunnel vision. In tomorrow’s battlefields, a WSO that operates the defensive avionics and cues sensors will be essential to survive Russian IADS.

    A tapering wing with optional LERX and a reverse sweep on the trailing edge, low mounted. Less wingspan does not necessarily mean less wing area, with correct design. The DH Mosquito and DH Hornet had formidable low altitude agility and performance for twin engine fighters of their period.
    Twin engines, fuselage mounted above the low wing, podded as in the AirLand Scorpion albeit with less body blending. The Scorpion seems like it would have a pretty long jet tube and associated thrust losses with its current arrangement of an extended exhaust out to the tail assembly. No doubt it helps with IR signature.
    Tandem cockpit with rear seat slightly higher than front seat. Bubble canopy for visibility; though the front canopy would require armoured glass rated for lower caliber cannon for ground attack reasons.
    Twin tail empennage for redundancy and greater rudder authority. This is important for strafing.
    All metal construction using Al-Li. If the Pucara can survive 20 ADEN 30mm cannon shell hits; so too should a properly armoured, all metal aircraft with stronger alloys than duralumin.

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33. Very interesting proposal… could you elaborate on the landing gear? Are they fixed or retractable? Why is nose gear behind the main landing gear?

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    1. It is not nose gear, it is tail wheel. I decided on fixed gear for simplicity, and figured that would be the best layout – using nose wheel might interfere with gun operation and maintenance, whereas wing gear allows easy access to most important things in the aircraft (gun, ammunition etc.).

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34. Picard, have you seen this? It’s a Youtube channel that a lot of retired test pilots, naval aviators and airmen present on. https://www.youtube.com/user/PeninsulaSrsVideos/videos . They even have X-plane test pilots present on it. One thing that caught my attention was X-29 test pilot Kurt Schroeder: https://www.youtube.com/watch?v=LOmvrk3LPGc talking about the forward swept wing program with DARPA, NASA and Grumman.

    The promise of forward swept wings has been the increased lift and reduced drag all the way from subsonic to transonic speeds along with increased agility. To go supersonic, however, requires a lot of structural reinforcement or clever engineering with composites to make the wing flex back down as opposed to flexing up and providing a positively reinforcing lever moment at the wing root.

    But what if the plane was never intended to go supersonic?

    Then you have a plane that is extremely agile at low speeds, a wing box that is moved rearward, thus providing a good amount of internal volume at centre of gravity, and a lot of lift at take off and low stall speeds for STOL purposes.

    Now, what’s interesting is that Schroeder mentions that it is commonly perceived that FSW is highly unstable when in fact it was untrue. Instead, since the X-29 program was intended to push the boundaries of agility in the transonic regime, the designers purposely put in canards providing 25% overall wing area to promote 35% instability. Without the canards, the X-29 was statically stable, but still retained its high lift and agility at low speeds (although obviously less without the canard contribution).

    The other thing Schroeder mentioned was that the X-29 was never designed, at any point, to accommodate in-flight refuelling. That meant a support crew followed the plane around to constantly refuel it. At one point they flew 6 1 hour sorties in a single day. The size of the support crew and maintainability was never mentioned (this is an X-plane, not a production plane) – but this is still highly impressive for something that they effectively cobbled together from scraps: engine from F-18, FCS from SR-71 and so on.

    Now, for purposes of combat power, a forward swept wing design might not be the best idea in terms of maintainability. But it is notable that a design hailing from WW2, the Ju-287, flew with a forward swept wing – a twinjet bomber with bomb bay centered at CoG so there were less issues with trim after munitions release. The sweep angle was quite shallow – we are talking WW2 metallurgy and aerodynamic design here – but the relative success – and the fact that the Ju-287 would later go on to inspire the Hansa airliner and Russian Su-47 – does speak to the possibilities inherent to such a design.

    A forward swept wing would allow for a truly massive cannon to be mounted at CoG, without interference from tricycle landing gear; and with less concerns over trim, or having to re-balance fuel as ballast as munitions are expended. The X-29 had a conventional, buried rear engine, but the Hansa Jet has a podded engine configuration comparable to the A-10: https://en.wikipedia.org/wiki/Hamburger_Flugzeugbau_HFB-320_Hansa_Jet . The increased distance between cockpit and wing root also means a greater degree of cockpit visibility compared to a mid-mounted straight wing.

    A more recent implementation than the Su-47, would be the Russian SR-10 trainer: http://kb-sat.ru/projects/cp10.shtml (google translate required) . Look at how small the designers were able to make the aircraft: https://www.youtube.com/watch?v=TG65G0_P6y0 . In such a tandem seating arrangement, a simple straight wing would put the wing box and wing spar through the rear pilot seat. The forward swept wing thus allows the design to be smaller than what would normally be possible (or at least, shorter in overall length). The SR-10 trainer is designed to be benign handling (due to being a trainer) while still having agility enough for aerobatic training. Being Russian built, it is robust enough to take off from Russian quality airfields.

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    1. Quite interesting, thanks.

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35. As it turns out, there is in fact, nothing new under the sun. NASA explored the possibility of a forward swept wing close air support aircraft – back in 1991: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19920012322.pdf

    The design is a -17.8% unstable, fly by wire, electrically actuated, twin engine FSW canard aircraft. It mounts, like every CAS design study, a GAU-8a gatling gun and can put on up to 20 bombs of 500 pounds size. It has a takeoff distance shorter than the A-10, carries more ordnance, flies faster, and stalls and lands slower than the A-10.

    Unfortunately, there is no discussion whatsoever on armouring while the use of a forward swept wing necessitates the use of composites; which limits armouring options (but does not necessarily mean that a composite wing is less survivable than an alloy wing, but it does mean that it is harder to repair). The authors instead emphasise the superlative manoeuverability as a survivability feature in of itself.

    Still, a similar design removing the canards for neutral stability; or moving components to bring Cg closer to Cp will already go a long way towards removing much of the cost inherent to the aircraft. A FBW system may still be desirable due to enabling electrical actuation, which has advanced remarkably from the days of the A-10’s initial inception. The designers deliberately placed the wing and engines as far to the rear as possible. Even the cannon was moved as far back as is practicable; to the point where the front landing gear’s position is impacted; though this is partly due to the placement of the ammunition at Cg. A more forward cannon placement (or a heavier cannon) would do a lot to stabilise the aircraft. Armouring the cockpit, also. Finally, the designers opted for podding all sensors for full flexibility. A permanent FLIR on the lower nose and/or an IRST would do a lot to assist in flying under the weather or at night while freeing up hard points.

    Payload can be sacrificed to reduce the wingspan – which reduces the cost as well. Still, it’s remarkable how much the forward swept wing can contribute to how the aircraft flies – at a 15 meter wingspan it is a full 2 meters less in span than the A-10; while having better STOL capabilities, shorter re-attack time, greater speed and greater payload. Certainly, this is not as small an aircraft as your proposal at 12 meters in span. Unfortunately, at least some of that performance is based upon the design characteristics of a paper engine. I can’t find the exact performance characteristics, but apparently it was in this RFP: 1990 AIAA / General Dynamics Group Student Design Competition – Undergraduate, Request for Proposal . Guessing at the thrust using T/W (0.635) and gross takeoff weight (48,820 pounds) this would imply that at 50% (4927.5/9855) fuel the 0.635 ratio is achieved by 2 engines outputting (48820-4927.5) x 9.8 x 0.454 x 0.635 = 124007 newtons = 62003.5 newtons each. The authors allocate 2319 pounds (1060 kg) to each of them. This basically puts the engine into the range of the CF34-8c : https://en.wikipedia.org/wiki/General_Electric_CF34

    It’s an interesting project. Were it to actually be built, it would probably outfly even some air superiority fighters at low altitude. It would probably end up like the Su-47 (albeit smaller). It’s interesting how the engine winds up so similar to that of the A-10 (albeit heavier and more powerful).

    I think that were the design shrunk somewhat so that the payload matches or is slightly inferior to the A-10, while mounting the Oerlikon KDG it would be quite formidable. Especially given that now, Supershot has been revived for the Bushmaster 35mm chaingun: http://lem.nioa.com.au/products/view/258/5/weapon-systems/orbital-atk-bushmaster-iii-35-50mm-cannon – we may even see a 50mm supershot for the KDG going forward. This would match the CTA CT40’s muzzle energy at the cost of greater ammunition volume but at much greater rate of fire. The Supershot is designed so that it does not affect the stored kills of IFVs so upgunned; while the round being simply necked up to 50mm means that the only changes required for the KDG are a new barrel – the extractor, revolver chamber, and electric motors should all be unaffected; just as it is for the Bushmaster. Even were the electric motor to be slowed down by the increased ammunition weight it has to spin in the revolver chambers, it would still result in a greater thrown weight than the GAU-8, at higher accuracy and longer range; which implies either longer burst lengths or increased engagement distance. Both are beneficial; but especially the accuracy means greater assurance when operating at danger close ranges.

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    1. Problems I see with swept wing are primarily construction. It needs to use composites, and is overall very stressed in flight. This means that even minor damage might have unacceptable impact on aircraft survivability, and damage will be hard to repair in the field. In fact, I thought about full-stell CAS fighter, or a composite of titanium and kevlar, but a titanium-only aircraft might be the best (cost notwithstanding).

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       1. Very true, but still, that the Germans were able to build aluminium wings (probably duralumin) in the Ju-287 and the Hansa Jet doesn’t necessarily mean that a composite wing is required. In the book “Design for Air combat” the author states that up to 15 degrees reverse sweep can be tolerated with “traditional materials” – by which I presume to be aerospace alloy. A titanium only aircraft would be less stiff than that of aluminium, but the strength per weight would presumably make up for any penalty.

          Steel might work, but its density limits its applications to landing gear and so on. An all steel airframe would require engines too powerful and thirsty (but it would definitely be survivable). In terms of unconventional materials, as long as we are in the hypothetical, why not go insane and just build the aircraft out of armour plating? https://en.wikipedia.org/wiki/Advanced_Modular_Armor_Protection

          Mat 7720 new is an Al-Ti alloy that provides the protection of RHA at 38% weight penalty (density increase not disclosed). Now, the problem with armour plate is that while it is highly protective, little thought is given to its workability into complex shapes. It is partly why AFVs and MBTs these days have these slab sided looks to them. The problem with Al-Ti alloys is that they are hard to work with; requiring an argon atmosphere; or a cover gas around which a gas-tight bladder is sealed for the work. As to whether they might be able to produce the complex, rounded shapes required of an aircraft, remains to be seen. The implementation of Al-Ti alloys in aerospace applications is already widespread, however.
          http://www.rtiintl.com/Titanium/RTI-Titanium-Alloy-Guide.pdf This shows the various grades and alloys available.

          An all – Al-Ti alloy airframe would be unprecedentedly light, stiff and strong; but at 30 dollars a kilo of material compared with $1.50 a kilo, it is pretty hard to justify.

          On the other hand, the airframe could probably withstand direct strikes with expanding ring missile warheads; were a semi monocoque construction adopted. Making an airframe out of armour plate tends to have those benefits. On the other hand, the materials alone would make it cost closer to that of aircraft ten times as large.

          Anyway, the point of bringing up the NASA study wasn’t so much to extol the benefits of a composite wing as it was the FSW. Even at lower sweep angles at the limits of conventional materials, there were benefits in terms of internal arrangement, agility, and handling characteristics. Using, say, a titanium wing spar could probably extend that maximum allowable angle. And in any case, since the aircraft is not intended to go supersonic, merely transonic, the requirements would be lower.

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       2. “It is partly why AFVs and MBTs these days have these slab sided looks to them.”

          Well, the main reason are the materials used – ceramics etc., which are hard to use in rounded turrets.

          “Anyway, the point of bringing up the NASA study wasn’t so much to extol the benefits of a composite wing as it was the FSW. Even at lower sweep angles at the limits of conventional materials, there were benefits in terms of internal arrangement, agility, and handling characteristics. Using, say, a titanium wing spar could probably extend that maximum allowable angle. And in any case, since the aircraft is not intended to go supersonic, merely transonic, the requirements would be lower.”

          Yeah, that is true, but I am still sceptical about damage survivability – stresses involved in FSW mean that any damage is more dangerous.

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       3. Titanium is still expensive and very hard to work with, but the costs are coming down – I think that with aggressive research in materials sciences, it could be done someday. A spall liner might have to be put around (titanium armor does tend to spall when hit).

          This is one area I expect innovations in the civilian sector will translate into military innovations.

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    2. I’d be worried about aeroelastic twisting with a forward swept wing.

       Another question is how well this will survive battle damage. If it depends on FBW, that could be a serious problem if the system is ever taken out and you would need redundancies (which adds mass and cost).

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    3. It would be truly awesome to see a 50mm KDG on a CAS aircraft. I’d be willing personally to sacrifice payload heavily for more ammo. I suspect that some parts outside of the barrel will have to be upgraded or perhaps a slowdown in the burst rate of firepower. The ammo would be heavier regardless.

       Even so, it’d be worth it. Plus you wouldn’t need as many bombs to begin with, given the power of the gun.

       The only other useful payload may be jamming equipment or perhaps some sort of sensor (I’m thinking IR) for locating enemies (especially tanks and similar vehicles).

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36. Picard, what do you think of the Canadian C-100 as the basis for a CAS aircraft?

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    1. 35 meters in length, that is a strategic bomber, not a CAS aircraft. A CAS fighter should be no more than 15-20 meters in length, tops. Shorter if possible.

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       1. Forgive me, I meant CF-100… you mentioned to me that you were interested in engine placement similar to the Su-25, I wonder if it would be a suitable base aircraft.

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       2. Yes, I think it would be suitable. Only question is mounting big enough gun, but Id on’t think it would be an issue with a new design based on such configuration.

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37. One option might be to consider a mix of single and double seat versions. The single seat versions would have to operate with the double seat versions though. Not sure what the singe to double seat ratio would be.

    The advantage of a single seat variant is the opportunity for more bursts or perhaps more fuel (or some trade-off between the two).

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38. Alright, I think we need to actually spell out the jobs that our attack planes need to do.

    1) Pure reconnaissance
    -fantastic loiter time
    -very low cost/logistics

    2) Opportunistic attacking/light CAS
    -great loiter time
    -M2 size machine gun
    -possibly light armour

    3) Heavy CAS
    -very good loiter time
    -Big main gun
    -Lots of ammo for that main gun
    -Mix of rockets/missiles on wings for various threats

    4) Anti-Armour operations.
    -solid loiter time
    -Enourmous gun
    -Heavy missiles

    5) Battlefield Interdiction
    -Higher cruise speed and distance
    -Higher payload

    If you were to design a plane to be a “pure” performer in any one of these roles you would get a fantastic plane, but I actually do think some multirole capability is intelligent here, sort of like your single FAC and ALX to cover all five of these jobs. One of the hilarious things about the A-10 Warthog is that it is actually the most Multirole aircraft in the entire USAF inventory because they ask it to do all of these things. It’s also of course the plane they want to get rid of most dearly, despite literally being the cheapest. Anyway, I actually think that there are some problems with my list that I intentionally put in there, which I will try to address in later comments as soon as possible.

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    1. Starting with the very last role of Battlefield Interdiction, this is the role that people who try to get fast flying jets to replace actual CAS support planes love to focus on, and for good reason. This is the one job that paper thin jets are almost as good at as dedicated CAS planes. The maximum payload on the A-10 is 16,000 lbs. I can’t find the maximum payload of the F-18 but I assume it’s similar. The Warthog has an advantage in actually finding its prey, but the F-18 may have an advantage in speed of deliverance.

       For example, if you know that an enemy convoy is traveling on road 18, then in that very specific example the many benefits of the Warthog don’t really matter as much, and what matters more is payload and speed of deliverance. Even in that situation, the ability to fly low down, bring guns to bear on the lighter armoured vehicles, and change the loadout to make use of more, smaller missiles/rockets using advantage of the closer range (and improved accuracy of the same weapons), all combine to make the Warthog clearly better even in that particular mission. On top of that, there are many cases of short range interdiction that arise spontaneously, and the A-10 gets more useful the more the interdiction switches from strategic->operational->tactical.

       But the point is that a plane such as the F-18, or even, god forbid, the f-35 isn’t actually a total joke as an interdiction aircraft. Even there, they’re not as good as the heavy CAS planes, but they can actually add some value. But always remember the sleight of hand when people start talking about how the F-35 can replace the CAS aircraft in their role, they’re talking specifically about this one job. And they’re not even as good at it anyways.

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       1. Thing is, aircraft always has a “primary” mission and secondary ones. And primary mission should always be the most difficult one – and in this particular case, it would be CAS, not BAI. Of course, there are political reasons for focusing on less difficult missions, so as to make underperforming designs seem better than they are (F-35).

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    2. Indeed. There are actually “families” of related missions, so that aircraft which perform missions from any single “family” are very good at their job, whereas performing work from two disparate “families” ends up involving major compromises. That is what I was aiming for here; single-role aircraft would have been even better than my designs at their chosen missions, but it would result in too complex logistical system due to many disparate types.

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       1. Ah, refreshed my page after posting my comment below, so I did not see your comment. Anyway, yes I think we’re in agreement that there’s a small amount of overlap in functionality that makes the Attack/Fighter airplane actually not completely useless. Nothing even approaching the ability to do CAS, let alone tactical reconnaissance, but they do have limited anti-armour capabilities, and pretty solid bridge-bombing capabilities (and related strategic/operational strikes). An actually good fighter/attacker, such as the Rafale, would actually be even better in some roles, since it could better conduct quick operations over “hot” airspace, which would lead to the plane having to defend itself. Even this is largely irrelevant however, as the loadout for bombing makes the plane heavier and sluggish, as well as not being equipped for A2A, and it’s probably more intelligent most of the time to have a fighter pair escorting the real CAS planes in that role.

          But I suppose my point, and I don’t want to speak for you but I get the impression you agree with this, was that there may be a small niche for a sort of workhorse plane such as the CF-18 my country has, even if we also had a true heavy CAS plane such as the A-10. This would be especially true if we had a much smaller (and cheaper) plane that had to do FAC well and sacrificed size and payload to do that.

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       2. I think the reason why air forces went for multirole planes – part of a reason, at least – is that they still live by Douhet deep / strategic bombing doctrine. And in deep strike, multirole fighters are indeed superior to CAS aircraft, as they are faster, even with air-to-ground payload.

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    3. Anti-Armour operations can basically be boiled down into two different categories, killing MBT’s, and killing everything else. The requirements for actually doing this job well are:

       1) Loiter time
       2) Low flying – (Armouring)
       3) Slow speed
       4) Armour destroying weapons
       5) Lots of ammo for those weapons

       Clearly, CAS aircraft are far superior when it comes to killing non-MBT’s. The ability to fly low and slow to find enemy vehicles, as well as bring an accurate gun such as a GAU-8 down upon them makes them totally superior in this role. It’s really not comparable. On the other hand, while something such as the A-10 can better find enemy tanks, I’m not entirely sure that the 30mm GAU-8 is effective against them, and neither are the A-10 pilots, who believe it to be able to get low-percentage mobility kills and not much more. The main weapon the USAF uses against enemy MBT’s is the Maverick missiles, which are pretty damn effective (and expensive). The A-10 still has an advantage over, say, the F-18, in actually finding the tanks, and also firing much closer, but in terms of killing them payload matters the most.

       All of which is actually largely irrelevant, because tanks need their lightly armoured groupies anyway. The amount of onboard “kills” contained in an A-10 against light tanks/trucks is a great deal higher than the F-18, due to the big gun and the ability to actually fly low enough to use it. But I do want to say that once again, in this very specific niche of “you have some enemy tanks out in the open” high, fast flying jets actually do provide some value when armed with the appropriate missiles. The problem is people don’t understand the limits of the aircraft, and poorly understand the nature of CAS, which is far different from “just go kill some tanks that are undefended and which we have perfect intelligence on”.

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    4. For the last three I don’t think I need to do much expanding here, what with preaching to the choir. At this point the idea of a paper thin, high flying, fast flying, fuel guzzling, jet doing any of: Heavy CAS, Light/Opportunistic CAS, Reconnassaince/FAC, is a total joke. They just can’t do that, and it’s totally ridiculous to think that they can. However, in brief:

       For Heavy CAS you need a thickly armoured plane, 30mm or equivalent gun, lots of ammunition, tons of hardpoints on the wing for weaponry, great low speed maneuverability, great cockpit visibility, possibly two seater, and hours of loiter time patrolling a very small area.

       Opportunistic Light Attack/CAS sacrifices some armour, gun size, and wing weaponry for superior loiter time, lower cost and logistics, smaller size, and even better low speed maneuverability.

       For pure Reconnaissance/FAC technically you wouldn’t have any armourment or armour, just an incredibly cheap, tiny plane, that can loiter for hours and hours at a time really soaking up the detail of the area being patrolled.

       *Although I should mention that this is Tactical Reconnaissance we’re talking about here, high flying jets can do a decent job of Operational/Strategic Reconnaissance. Basically giving you a glimpse of the battlefield from the perspective of a passenger airliner. Legitimately some value in terms of range, but sacrifices heavily on detail.

       As Picard has already expanded upon the Reconnaissance/FAC role and airplanes, culminating in the FLX, as well as the Heavy CAS mission and airplanes, culminating in the ALX, it’s sort of a waste of everyone’s time for me to do so poorly again. I still think it’s somewhat useful just to have all the bullet points together in one place.

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       1. Yes, I created a light CAS aircraft proposal, but in the end I decided to combine FAC and light CAS. Reason for this is in part because FAC aircraft is more likely to run across guerilla and/or masked enemies, and if that happens, it needs to be able to immediately attack them.

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39. One of the frustrating things with CAS being such a neglected mission is that the weaponry to effectively do it, and do it cheaply, seems underdeveloped. Canada produces the CVR-7 rocket, which can be put in a pod that, taking up one wing pylon, gives you 19 rockets, and you could probably make bigger rocket pods anyway. Our army found that training rounds for these rockets were penetrating the armour of Centurion tanks, so an anti-tank round was created that’s basically similar to a sabot, which can consistently penetrate the side and top armour of a T-72 tank. The accuracy of these rockets is 3 milliradians, which is actually greater than the 5 milliradians of a GAU-8 gun. They’re also incredibly cheap.

    Even by themselves these can get mission kills on MBT’s, since they actually penetrate deeper than GAU-8 bullets, and are more accurate, but there’s no reason that we haven’t developed 80mm rockets, like the Russians, or the 90mm rockets that, well, that the Russians developed in the M-79, and I can almost guarantee that a volley of those fired at the top, side, or rear armour of any tank in the world would result in an operational kill at the very least. Of course, actual testing needs to occur, and my impression is that even the 80mm rockets would be more than enough to destroy a tank, and possibly even better due to being able to carry more on the wings.

    On top of all that, rockets are amazingly versatile, just like the main gun of a tank. The CVR-7 can carry a bunker-busting head, a flechette head (vicious), or an anti-armour head. It’s a fantastic weapon system, and unbelievably cheap, and incredibly accurate. The only “problem”, is that it’s a close range system, with a range of less than 3 kilometers.

    But close range is a serious problem when you’re trying to pretend that your high flying jets are all that’s needed for CAS. So that’s why we never developed the obvious evolution of slightly larger rockets for A2G operations. It’s quite frustrating really. At least in the meantime we have Maverick missiles that do the trick, albeit hogging an entire pylon, and at greatly inflated cost.

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40. Picard, the more I think about a good CAS plane, the more I’m convinced that it needs to be a turboprop. As far as I can see there’s only one major drawback, and that’s if the propeller itself is too vulnerable to gunfire. Considering that you can make propellers out of steel (they used to all be steel or aluminum), and the base of the propeller is very large and thick, this should only be a problem with the outer edges, which are going to have some protection in flexibility and angle away from forwards. Lots of testing needs to be done, so I’m wondering if there are any reports of steel propellers being consistently damaged by gunfire, such as on WW2 planes, or OV-10 Broncos, or IA-58’s. It’s unfortunate that I’m in no position to actually effectively test this, but I’m starting to believe that a turboprop can actually be more armored than a turbofan, just because it has little open space, and so you can armor the engine itself much more.

    Anyway, what you get with a propeller is just so much compared to even a high bypass turbofan. The low speed, low altitude efficiency could translate into even more effective thrust with a comparable engine, and the fuel efficiency is simply unmatched. Taking a look at your ALX, it has a combat takeoff weight of 13,500k kg’s. Comparing that to the Super Tocano, which has max takeoff weight (per wikipedia) of 5400 kg’s. Let’s say that the Super Tocano is usually taking off at 5000 kg’s. It has a single 1600shp engine (the PW PT6-A), which gives the plane a HP/kg ratio of 0.32:1. If we take your ALX, and we give it two PW 127 engines, with 2750hp each, the plane has a total HP of 5500, and a HP/kg ratio of 0.407:1, which is higher even than the Super Tocano, a plane that I’ve never heard anyone claim is under-powered.

    Looking at a different airplane, the OV-10A Bronco that the Americans used in Vietnam has a max takeoff weight of 6,500 kg’s, and two 750 hp engines, combining for 1500hp and 0.23:1 HP/kg ratio. The most consistent complaint that the pilots had was that the plane was underpowered, so they came out with the OV-10B, which was basically the same plane except with two 1000hp engines. This solved a lot of the power complaints, at a HP/kg ratio of 0.301:1.

    Now, we don’t just not want to be underpowered, but if we gave the ALX two PW 127 engines I can’t imagine it even possibly having too little engine, and in fact we may want to give it a cheaper engine, such as the PW 124, since the PW127 reportedly costs about 1 million each. But my point is that there exists an engine that we can give to the plane that will give it better low speed performance, and (much) less fuel consumption, for probably lower cost.

    I’d like to hear the counter arguments for the turbofan route.

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    1. There are actually few drawbacks to a turboprop design. First is, as you mentioned, vulnerability. Other than engines being forward (this can however be solved with a pusher prop), prop aircraft cannot be as armoured due to thrust limits. Second is maneuverability – you need good acceleration to pull out after a gun run and avoid return fire, and prop designs are not very good at that.

       Anyway:
       https://defenseissues.net/2014/08/16/forward-air-controller-aircraft-proposal-revised/

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       1. With respect to the armouring, I believe I read on the comments here that the armour of the A-10 is 6% of its empty weight. That’s not nothing, and, since the thickness need is constant, it would be a slightly higher percentage of a smaller plane, but honestly that doesn’t seem too crippling. For starters, the CAS plane isn’t all that small, but even if armouring takes up 10% of the weight of the plane, that still doesn’t seem to be all that much.

          As far as thrust is concerned, there is no direct conversion between SHP and Thrust, but I found an equation that attempts to approximately convert:

          Fn = SHPx375xProp Efficiency / Speed in MPH
          *assume 0.8 propeller efficiency

          So a PW 127 which produces 2750 SHP would produce, at 200MPH (320km):
          27503750.8/200 = 4125 lbs thrust.
          At half the speed (160km) which is the low end of what it might be at it would produce the equivalent of over 8000 lbs of thrust, and at a realistic speed of 240km’s it would produce 6187.5 lbs of thrust.

          This formula doesn’t take into account the effect of altitude, and it is quite clearly crude. Having said that, since propellers efficiency decreases with altitude it will be at it’s absolute best performance exactly when you need it, after an attack pass. There may well be some very important aerodynamic feature I’m simply forgetting, but propeller planes seem to have pretty good maneuverability provided they have enough power. Finally, considering that your ALX has a combat weight of just over 10,000 kg, the HP:weight ratio is enourmously higher than in your OLX, which never seemed unmaneuverable on paper to anyone.

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       2. Thanks.

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       3. Secondly, I understand that turboprops have thick blades, but I can’t imagine them withstanding gunfire going into them, especially since the gunfire won’t just hit the fan blades, but will potentially go into the core of the engine itself. In contrast, only the propeller is exposed in a turboprop, which give it far smaller area of vulnerability (since the prop is mostly empty space), and far more opportunity for armouring the fragile turbine core itself. On top of all that, obviously carbon fiber is right out, but I still think that, with a thick enough steel of aluminum alloy, a prop could potentially be fairly hard to destroy even when hit.

          It’s very frustrating because I’m not a big fan of purely theoretical discussions. The truth could be that propellers are totally superior to turbofans provided they have a thick enough steel propeller, or it could be that they’re totally fragile and unusable no matter what. I suspect not, but I’ll never know unless someone gives me a NATO rifle and a prop to fire at.

          The best I can find from the internet is that it takes, at 90*s, at least 3/4’s of an inch of steel to stop a military round. That means that the base of the propeller should be fine, and the most twisted areas could be fine, but the thinnest areas at the end may well be impossible to defend. Of course, damaged propeller blades are actually not that bad provided they don’t bring the plane down with them, and that they can easily and cheaply be replaced after the mission is over. I really just don’t have the capability to answer either question.

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       4. Problem is actually the engine itself. Casing can be armoured, but air-cooled engine would be better than liquid-cooled one. There is also an issue of thrust. In ALX, you need enough thrust to counter recoil from its gun, which I calculated at 26,5 kN. Two engines you mentioned in an earlier comment would provide 55 kN, which is more than enough, but you also need to compare engine volume and weight to ones installed.

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       5. Apologies for my very late reply. I have been on vacation, and blissfully away from any computer.

          Addressing the issues of the engine. For starters my idea was to have an air scoop to cool the engine located above the engine, and which then directs air downwards on to the engine. That way there is no angle for any bullets to penetrate directly into the engine. This would increase weight by a little bit, and drag by a bit more, but ultimately, without crunching the numbers, I feel that is pretty minimal. The back of the engine casing also has a duct on the top which allows the air to escape. We can fiddle around with the exact placements, but I don’t think it will be that much of an issue to get the engine the cooling it needs.

          As far as the weight and volume is concerned, the PW127 has a height of 33 inches, width of 26 inches, and length of 81 inches, and weighs about 1000 lbs. For comparison, the ALF 502-R has a height of 55.5 inches, width of 47.8 inches, length of 63.7 inches, and weighs 1,336 lbs. So the PW 127 is smaller in all dimensions except length, and is much less heavy. Considering that at low altitude and speeds the effective thrust generated is much more you could probably get away with an even smaller engine. I can’t find the cost of the ALF 502-R, but considering the cost of comparable turbofans it’s probably a lot more.

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       6. Issue with liquid-cooled prop engines is not the location of air scoop, these can be protected, but vulnerability to damage. If air-cooled engine is damaged, you only have a minor loss of cooling efficiency. If liquid-cooled engine is damaged in cooling apparatus, the cooling liquid runs out and causes a major loss in cooling efficiency.

          I used PT-68C for my FAC proposal (and yes, it can double as a light CAS aircraft):
          https://defenseissues.net/2014/08/16/forward-air-controller-aircraft-proposal-revised/

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       7. Turbo prop types are better when you need to have high sortie rates from rough airfields close to the front lines. They can take off quicker and reach targets that are close to the air strip very fast. They represent an alternative to helicopters.

          The A-10 is slower than the F-16 and experience has shown that it sometimes takes it too long for it to reach targets when called for support. The F-16 has the ability to reach those same target a lot faster than the A-10 and that is why when there are few airfields and you need to cover a large area the Air Force preferred to use the F-16.

          But the A-10 is more persistent and as mentioned by others can carry a higher ordinance load. This last is important and I do not know how well it has been discussed but the range is affected by the ordinance load and here for any equivalent load the A-10 is better attack plane.

          My personal feelings about turbo-props is that they are for really low cost wars or rugged environments. They lack the speed, range, load, etc. But when cost matters they are often preferred by very practical military. Something that clouds their utility is that so many of our current propeller attack aircraft are trainers with complex cabins that mimic jets. If you un-complicate the aircraft they could be cheaper.

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       8. Well, even insurgents now have MANPADS, so one of factors which increases price are self-defense systems. But turboprops are still more survivable than helicopters.

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       9. The problem with the A-10 taking too long to reach targets is a culmination of a few different things. Firstly, and most importantly, they never built enough of them, and then they retired half of the ones they built, so they have chronic shortages of the A-10, which means that instead of having them providing scouting support, and immediate CAS, they have to wait until shit gets really hairy and then call them in. In that situation then yes, the faster plane has a big advantage over the A-10, but that’s not really CAS done right.

          Secondly, as much as we all appreciate the A-10, it actually kind of sucks in a few ways. It is a massive plane, that takes far too much maintenance, and is quite far from being a practical dirt strip aircraft. A cheaper plane that can be co-located with the troops is an absolute necessity, and is one of the major reasons why I think CAS planes should have turboprops unless given a very good reason otherwise.

          As far as lacking payload I simply don’t agree with that statement. The TU-95 is a turboprop, does it lack payload? The type of engine used to generate the power is pretty much irrelevant, only the power/thrust generated matters, and since a turboprop is far more efficient at generating thrust per weight, at the low speeds and altitudes of the CAS mission, the turboprop engine is lighter for the same thrust, which means you actually get more payload. To put it in perspective, I proposed above replacing the ALF 502-R with the PW 127, which generates more effective thrust at low speeds, and is 300 lbs lighter per engine. That’s an additional 600lbs of payload that you get for free. So I think you may be confusing the applications of the technology with the limitations of the technology.

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       10. Issue I see with turboprops is a likelyhood of damage when operating from dirt strips. CAS aircraft would need two engines, similar maybe to P-39, so propellers would be close to or even behind the nose wheel. A FAC aircraft can do with one engine however.

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41. Picard,

    Another thing that I forgot to mention with respect to the turboprop vs turbofan debate is that the turboprop is far more efficient with fuel. Well i mentioned that, but I overlooked one of the conclusions, which is that a turboprop aircraft needs less fuel to go the same range, and far, far, less fuel to slowly loiter over a battlefield at 160kmph or so. What all that adds up to, is an aircraft that doesn’t need as much internal fuel as the same aircraft but as a turbofan. You could probably get away with a fuel fraction as low as 30%, or even 25%.

    I say that because, based upon some graphs I found of airspeed versus turboprop/turbofan/turbojet efficiency, even at a speed as high as 360kmph, the turboprop has 45% more efficiency than the high bypass turbofan, and the effect increases as the speed decreases (although not as much as I had previously thought, because turboprops actually become more efficient at higher speeds up to a point). High bypass turbofans only start becoming more efficient than turboprops around 720 kmph, which is above the top speed of these planes anyway. Of course, all of this depends on the specific engines, and the prop design, but it is just a general rule.

    What that means is that, for the same effective thrust generated, you are, realistically, using 31% less fuel or more (1/1.45=0.689). On top of that, because the engines themselves are lighter, you need less thrust to simply stay in the air, although that might be a wash with a payload increase, but then you get an increased payload. However, if we are using about 30% less fuel to generate the same thrust, then we can just simply put 30% less fuel on the plane. That means that we can have an even smaller, plane, since we don’t need to carry all that extra fuel. It also means that we are going to have reduced takeoff weight, which means reduced takeoff distance and speed. Which we could then use to increase our payload, or simply enjoy. And all of that is using 30% somewhat unoptimistically, since fuel savings are more like 35%.

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    1. To use a real world example. Mainly using wikipedia as my source I’ve found the OV-10 Bronco had a typical takeoff weight of around 5000kgs. Internally the plane had a capacity of 954 litres, which it usually held Jet Fuel A in. At 15* Celsius, that JFA has a kg/volume conversion of 0.8kg/L almost exactly, which means the plane had a fuel weight of 763.2 kg’s of fuel. They typically added a centerline tank to the plane, which held 150, 200, or 300 gallons. Let’s say that they were always using 300 gallon tanks, which equates to 1152 liters of fuel. That means that the plane had a combined fuel capacity of 954+1152 == 2106 liters, which works out to a weight of 1684.8 kg’s. I’m sure that the plane was actually (potentially much) heavier than 5000kg’s at this point, but even still at this weight the plane has a fuel fraction of 33.7%. There are reports of pilots who flew them who actually complained that the plane had too much endurance. That after five hours of flying the thing it was too hard on the pilot to keep working. Some of them flew as much as 7 hours in the things, albeit mostly loitering.

       So in addition to simply being cheaper per flight hour, the savings in terms of fuel loadout are enourmous here. A much smaller fuel fraction gets the pilots actually more air time, just because the turboprop is so much more efficient than the turbofan. This in turn makes the plane much easier to design, and lighter overall, due to the decreased need for fuel tank size.

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       1. Yes, but in a more modern observation aircraft you could include an autopilot. Autopilot pilots along the set route, one crewmember observes the terrain and second crewmember sleeps until they switch. But it is true that fuel savings would be enormous, which is important in a frontline aircraft.

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    2. Yes, turboprop is far more efficient. That is why I used it for my FAC/COIN/light CAS aircraft:
       https://defenseissues.net/2014/08/16/forward-air-controller-aircraft-proposal-revised/
       Endurance of 9 hours, combat radius 1.850 km, fuel fraction 0,17, albeit estimates may not be entirely accurate.

       Turboprop aircraft is ideal for COIN work precisely because it does not need much fuel to loiter for long time, so it can have more armour, weapons etc. for given amount of fuel and range.

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42. So if I could make one last comment here as a sort of compendium as to the benefits of turboprops:

    -Cheaper to buy
    -Cheaper to maintain
    -~45% more fuel efficient
    —-Less fuel required in plane
    —-Cheaper to operate per flight hour
    —-More thrust for same fuel expenditure
    -Engine itself much more easily armoured
    -Lighter
    -Smaller width, height
    -(Negative) larger length

    The only real unknown is whether or not the propeller itself can be adequately and practically thickened in order to not be the weak link in the chain. If it can be, then I really don’t think there’s any benefit left to turbofans, although I’ll happily listen to others who can come up with reasons.

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    1. I also support the turboprop idea. Turboprops are much cheaper, lighter, smaller, more efficient than turbofans as you have already mentioned.

       You can look at current attack helicopters, like Mi-28 for ideas about the blades armor — ” A new design of all plastic rotor blades, which can sustain hits from 30 mm shells, has been installed on the Mi-28N Night attack variant.” (quote from https://en.wikipedia.org/wiki/Mil_Mi-28).

       I propose to use the P&W PT6 engine (https://en.wikipedia.org/wiki/Pratt_%26_Whitney_Canada_PT6) because it is already powering many trainers/light attack aircraft like the Pilatus PC-9, PC-21, Embraer Super Tocano (which is currently used as light CAS in Afghanistan by the US forces), and similar aircraft that are already widely used and well integrated in many of the western airforces. It also used in a huge amount of civilian aircraft and can be serviced in many locations around the world.

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       1. Great find with respect to the plastic rotor blades. Assuming this can be put onto a plane propeller, and there’s little reason to suspect otherwise, then we’ve definitely increased the survivability of all prop aircraft for CAS, including my idea of the modern A-1. However, I do still think that the raw thrust advantage of a turbofan is unavoidable, so I no longer believe that any turboprop fleet can totally replace a modernized A-10.

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       2. Although I should point out, I’ve been thinking of a sort of “Killer Bronco” idea that I’ve been having. Take the Bronco. Get rid of the asinine 1000 lbs of needless electronics, as well as the 1000 lbs of “it needs to be a dirtbike” landing gear. Get rid of the cargo compartment as well. Use our experience finding that a big gun and small frag bombs are the most useful at CAS. Then put in something like the Gsh-30, or some self-designed 30mm Gast Gun. Give it a few light utility pylons/sponsons for whatever you need. Now, for the coup de tat, give it the top of the line 1900hp PT-67A engines, and give it two of them, just like the original.

          According to Beckett, the original prototype plane had a loaded weight of 5800lbs, and less than 7000lbs when doing CAS in its original configuration. Assume our changes lead to an increase in weight when doing CAS to a full 9000lbs. That’s going to give us 0.42 hp/lbs ratio, which is absolutely nuts. Compare that to the 0.21 hp/lbs ratio of the BF-109 Messerschmidt, which I believe had the best P/W ratio of any production prop aircraft ever.

          An aircraft like that, which I’m calling the Steroid Horsie, could very well not work out for a number of different reasons. Potentially poor endurance, too much non-centered weight, etcetera. However, it’s worth a prototype or two at the very least.

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43. Now, on to the next point of interest, the gun. The GAU-8 currently on the A-10 weighs “only” 281 kg’s, but the complete weapon system including the feeder and ammunition drum with the ammunition weighs in at an amazing 1800kg’s. The GAU-12 weighs only 120 kg’s, but I can’t find the weight of the entire system. If we extrapolate using the GAU-8, then it should weigh about 768 kg’s. That’s for the 25mm version though. Using the ALX, the gun + ammunition collectively weigh 1027 kg’s, and I’m not sure whether or not you’re including the ammunition drum and feeder system in that calculation or not. I certainly like the amount of ammunition, but the weight itself is kind of ridiculous.

    I think the gun specifications are pretty open for debate. One of the problems I have with the A-10, and I love the plane don’t get me wrong, is that the gun was originally designed to kill 1960’s era Soviet battle tanks. Well tanks make up about 5% of the battlefield at an absolute maximum. Carrying around a gun that can kill them is awesome, but the weight penalty is quite high. We know from friendly fire incidents that the Bradley’s 25mm rotary cannon can disable Abrams tanks. If my above calculations are correct, then the weight savings from switching to a 25mm rotary cannon can be more than 60%, or over 1000kg’s. Furthermore, if you’re dealing with a bunch of tanks, then you really should be loading out with recoilless rockets with anti-tank warheads. That way you have the flexibility to carry them or not carry them, and you can also see which weapons actually work and which do not.

    When we focus on the other potential victims of the GAU-8 I think we can see that the 30mm explosive round is overkill. I know it might be sacrilege, but I would actually go all the way down to a 23mm or even 20mm cannon as the main weapon. You don’t want to skimp out on the weaponry, but the weight and volume savings are very difficult to ignore. You can pocket the weight reduction, or you can use it for more ammunition. The gun can still consistently kill thin skinned vehicles, can destroy machine gun nests, slaughters infantry out in the open, etcetera.

    Ultimately, to even have an educated best guess we need to talk to the pilots, soldiers, mechanics, and engineers. Figure out how damaging a reduction in per-bullet firepower would be to them in actual practical reality. Then, with an eye to what we can actually build, we can make a proper, well balanced gun. Although I will miss that lovely BRRRRRRRRRRRRRT of the Avenger.

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    1. Thing is, it is not just main battle tanks. There are many more protected vehicles on the battlefield: armoured personnel carriers, infantry fighting vehicles, self-propelled artillery, and there is also an issue of attacking bunkers, shelters and such. So gun still needs to have sufficient penetrating power, range, muzzle velocity, rate of fire and shell weight. You also have to keep in mind that you don’t need to penetrate armour of an MBT for a mission kill: destroying targeting and other sensory systems is quite enough. But while not inside the main armour, they are still protected, so I am not sure 20 mm gun is enough for that. Depends on the ammo, I guess.

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       1. Actually my thinking on this has evolved quite a bit. I was trying to make it work where we could use one single plane to replace the OLX and ALX, but I’m starting to wonder how possible that really is. The main reason being the gun that my “Destroyer” would need for Heavy Direct Fire Support. I now favour something very similar to your OLX and ALX concepts, although if I were made emperor of the world I would just build the modernized A-1 Skyraiders and modernized A-10 Warthogs, probably in something akin to a 10:1 ratio. You can do a lot with unguided rockets and bombs on hardpoints, to try to solve the lack of heavy firepower that the absence of a large caliber gun gives you, but those can’t really replace a heavy gun, and you’re still stuck with the low T/W problem for acceleration unless you put overly large dual engines on the thing, which causes lots of problems with fuel economy and range. So having said all that I got to thinking about what kind of gun we would need on an updated A-10.

          As I wrote with regards to your Fighter Proposal 6, in my opinion, by far the best gun for a fighter plane is a smoothbore sabot revolver-cannon, of which 20mm is probably a caliber that we can get away with using. The reason for this is pretty simple, when it comes to armoured targets, sabot rounds reign supreme. It doesn’t make any sense to have a HE round fired less frequently, at half the velocity, and with worse effects per round, because all we’re ever firing at are essentially lightly armoured vehicles. Unfortunately, we have something of a dilemma with our ALX, since we need its gun to destroy targets ranging all the way from MBT’s to exposed infantry in the open. The guns and shells required to do those two jobs are fundamentally at odds with each other, a Sabot penetrator for the MBT, and a pure HEI rifled shell for the infantry. That got me thinking, why not just have two different guns?

          When it comes to exposed “soft targets”, such as infantry, bunkers, aircraft on the ground, roads, runways, or even unarmoured buildings, we want as much explosive effect as possible. HEI gives us basically the effect of a frag grenade first slightly penetrating the target before exploding, for each round. If we were to upgrade the caliber of the gun on our ALX to 35mm, then we would expect a round weighing ~50% more, for the same velocity. Personally, I think we can go even lower. The velocity of the shell is relatively unimportant compared to the rate of fire, and the size of the explosive. A lower target for velocity, say of 800m/s, gives us a lot of weight savings from some combination of shortened barrel, as well as lesser propellant. To use the Oerlikon 35mm as an example, to get to a velocity of 1175m/s for its HEI projectile weighing 550 g’s, it takes a round that weighs 1.58 kg’s, giving a projectile/round ratio of 35%. This compares to the GAU-8’s 681 g HEI round, with a 380 g projectile propelled at 1020m/s, for a ratio of 56%. The GAU-8 has a barrel length of 2.3m, which is 7.67x its caliber, compared to the Oerlikons 3.15m barrel length, which is exactly 9x its caliber. So in order to get a measly 155m/s velocity increase we need to use massively more propellant and a much longer barrel, all of which add considerable weight. To get our lower velocity round we would in reality share the weight savings between barrel shortening and propellant lessening, but pretending that we keep the round weight the same, in order to go from 1000m/s to 800m/s we can shorten our barrel to 64.1% of the original length, and that’s ignoring the reality of increasing friction with increasing velocity, which would exaggerate these results even more. In fact, again ignoring friction which exaggerates this effect, if we outright halve the barrel length, we still retain a velocity of 707m/s. Of course, like I said earlier, we would utilize some combination of lesser propellant, along with a shorter barrel, but the point is that there are serious weight and volume savings to be had here from a lower velocity shell. All of this can be used to either upgrade to a larger caliber shell, or simply have a smaller version of the GAU-8 with lighter rounds, but the same projectile.

          As for the sabot round, due to the inherent high velocity of the round, we don’t need to build a particularly long gun with enourmous propellant charge. The effect against heavy armour is unparalleled, and when it comes to armoured vehicles I think the “snapshot” advantage of a revolver cannon shouldn’t be ignored. Additionally, the increased practical range strikes me as being of the utmost importance in the presence of enemy AAA. Probably most importantly, due to the radically different ballistics of the round we could never simply mix it in with the ammunition of the other gun, since nobody could actually aim with that. For that last reason we absolutely need a different gun, and since we’re already using a different gun there’s no reason not to use a smoothbore revolver cannon that’s really good at murdering armoured vehicles.

          With all that being said, I think that my upgraded A-10 would have both a 6-7 barrel 30-35mm rotary cannon shooting HEI possibly with some SAPHEI mixed in, as well as a 35-40mm revolver cannon shooting APFSDS rounds, to take care of those pesky MBT’s. Having said all of that, it’s not about what’s great on paper, but what is practical to design and build in an aircraft, effective in the field, as well as easy to maintain. It could well be that for layout reasons it makes more sense to have dual smoothbore cannons placed in the sides of the vehicle, similar to the IA-58 pucara layout. It might also be true that a rotary cannon is the wrong choice for the HEI, although I certainly hope not, but I have heard that the weight of the GAU-8 combined with the placement makes servicing the thing a pain. This is just the rough draft, and actual engineers, mechanics, and pilots would need to be brought in for revisions.

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       2. One thing I might add is that we don’t have to go entirely full anti-armour and full anti-personnel. We can utilize a mix of HE, HEI, and SAPHEI for the rotary cannon, and a mix of regular APFSDS, along with heavily frangible APFSDS for our smoothbore revolver cannon. The former is to give us a great mix against various soft and semi-soft targets. The latter is to make sure that we don’t just pass right through lightly armoured vehicles. The ratio at which these rounds should be mixed in is unknown to me, and would need to be decided on after experimentation.

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       3. It’s worth taking into consideration that discarding sabots… discard, and they do so directly in front of the muzzle, resulting in a cloud of sabot material to fly through and for the engines to injest – for your proposal it may be worth knecking down an existing cartridge instead. Regarding the use of revolver cannons for heavy sustained fire, preference may be given to a multi-barrel option such as a the Russian’s Gsh-xx-2s which have a lot of the same benefits if you can overlook the non-externally driven mechanism.

          Another point is regarding your mixed feed idea, it’s got obvious advantages but consider that different types of shells will have different ballistics, a HE rounds will not hit the same spot as a saboted penetrator.

          I would suggest triming some fat, drop the rotary cannon to 4 rifled barrels (no less for vibration reasons), if you’re only lobbing HE I am thinking 30×113 will work a treat, and for the larger cannon I would suggest using a regular 30-35mm cannon with 40-50mm barrels and working around the sabot problem, perhaps using a non-discarding sabot which would solve the weight issues but not the drag issue.

          I like where you’re going with this, I myself was playing around with a 30mm/105mm RCLR combination, keep me updated.

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       4. Picard, please delete my comment below at 1:36am. There was an error uploading this comment earlier.

          Yeah I’ve been thinking for the past week or so of this very problem. It’s actually worse than you think, because for the A-1 Skyraider, there’s a good chance that some aluminum sabot fragments will take off the propeller. It also means that my fighter proposal doesn’t work right either, since there is a good chance that the aluminum sabot fragments will get sucked into the engine intake. Even if the odds of any one bullet causing this is low, when you’re shooting ~2000 rounds/min from every single gun, then you have some pretty bad odds.

          To solve this problem I came up with a few frankly bad solutions. The first was to have a plastic sabot. This might work, but it’s frankly very questionable. Plastic sabots are used in shotguns (so low velocity), and 5.56mm and 7.62mm rounds, that don’t reach velocities of over 1km/s anyway. Again, might work, but there’s no real guarantee that the engine can just eat all the hard plastic any better than aluminum, and the plastic sabot will still potentially damage the propeller of the A-1.

          The second solution was to use ammunition similar to old HVAP or APCR rounds, which are the predecessors to APDS and then APFSDS rounds. Still, these give us very good muzzle velocity, at the expense of equally bad sectional density, which is probably better overall, but far from ideal, or even a guaranteed win over something like an APEX round. For reference, the US used some 76mm HVAP after WW2, which had muzzle velocity of over 1220m/s, but still suffered from accuracy issues.

          In the end, when it comes to AP, something like an APEX round is probably the way to go, alternatively PELE or FAP. For those who don’t know, an APEX round (Armour Penetration, Explosive) has a tungsten penetrator inside of it, and is wrapped in low density explosives. This gives it the advantages and disadvantages of the old APCR rounds, high velocity, but poor sectional density, but instead of an essentially useless aluminum case, we have explosives instead which are triggered on a delayed fuze. This means that, theoretically, we have explosives that propel the penetrator further into the object, as well as going into the created hole themselves. A great example of this is the Raufoss Mk 211 .50 cal bullet. We could probably tweak things specifically for AP, but the concept remains the same. Basically the advantage is that the light filler, being explosive, isn’t just worthless dead weight, like it is for the old APCR round.

          Unfortunately, while a combination of smoothbore gun firing APFSDS, and a rifled rotary cannon firing LV HE is an obvious win, if the revolver cannon has to fire APEX rounds at muzzle velocities of around 1150m/s, with much worse in flight characteristics than an APFSDS round, then we need to reconsider whether or not it’s really worth it to us to have two different guns. In this case something like the BK-27, with it’s 1100 m/s muzzle velocity is about as good as it gets. Pairing that with something very similar to the US M230, and its 30x113mm ammunition, fired at roughly 800m/s isn’t a bad idea. However, WW2 saw some experiments with very LV medium caliber weapons. For instance, the Japanese took the Oerlikon 20mm cannon, with its 20x72mm dimensions, and scaled it up to 30x92mm, which had a velocity of 710m/s, while only weighing a ridiculously small 51kg’s. Obviously, we want multiple barrels, and a higher rate of fire, but this is basically the direction we’re going in here.

          Even further in that direction, there was the German Minengeschoß guns, which had fantastic HE/weight ratios. The 30mm, for example, had explosive filler of 85grams, which compares very favourably with the GAU-8’s 56 grams. They ended up going with a 72 gram version for aerodynamic performance, but I’d argue that’s irrelevant when the rate of fire of the GAU-8 is taken into consideration. On top of that, the Minengeschoß round was a mere 30x90mm round, fired at ~540 m/s. Clearly very poor against fighter planes, but apparently effective against bombers, and exactly what we want out of our ground attack weapons. All being fired out of the MK 108 revolver cannon, weighing just 58 kg. A modern shell would have slightly lower proportional HE, in order to improve fragmentation, but the small amount of propellant and short barrels can be kept.

          The decreased weight of this gun allows us to really scale up the caliber. I imagine we can have a 35mm gun which, with the same 1000 rounds as the A-10, weighs just as much all together, and yet has enourmously more impact against ground forces. Couple that with, again, something similar to a tweaked BK-27 for armoured targets, firing high velocity APEX or PELE rounds and I think we’ve got ourselves a winner.

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       5. Nevermind, I’ve figured out the solution, squeeze bore cannons. The Germans already used this in WW2 for their 28mm/20mm PzB 41, 42mm/30mm Pak 41, and their 75mm/55mm Pak 41 cannons. All cannons performed very well, but were discontinued because the Germans couldn’t get enough tungsten for them, and steel simply shatters on impact at such high velocities. In fact, they found that the penetration from the 42/30mm cannon was almost equal to the 50mm Pak AT gun at 500 meters, which is extremely impressive considering that it can be considered a 30mm cannon in terms of ammunition weight, and less than a 42mm cannon in terms of barrel weight.

          The principle behind a squeezebore cannon is that you have a tapered barrel, and a shell that has angled hinges, that close in upon itself progressively as the shell is forced down the narrowing barrel. This gives us all the advantages of APCR or HVAP, which have a dense tungsten core wrapped in low density aluminum/plastic, but also the streamlined shape of an APDS round. In fact, I think it probably is superior to APDS rounds, but in exchange it requires a tapered barrel. The English also built a squeezebore cannon, or rather an adaptor for their 2pdr gun, taking it from 40mm to 35mm, and increasing the muzzle velocity (and the flight profile) to 1,143 m/s compared with the 792 m/s original velocity of the 35mm gun. They called this APCNR, for Armour Penetrating, Composite, Non-Rigid.

          Although due to the slowly shrinking caliber of the round, the pressure does not drop off as much as with a regular gun barrel, leading to greater efficiency for the same amount of powder, with the invention of superior APFSDS rounds it makes perfect sense that we would ignore the squeezebore APCNR round, just like we, for all intents and purposes, ignore APDS rounds for smoothbore guns. Additionally, since the hinges bring some challenges for rifling, the Germans started their rifling after the taper was over for instance, it again makes some sense to simply ignore for ground forces and use APDS even for rifled guns. But for aircraft, which can’t afford to fly through what is essentially shrapnel of their own creation, squeezebore appears like a godsend.

          As a matter of fact, I think this could be a big deal with small arms as well.

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       6. I meant to say in the previous comment, that this implies that we can now use this technology in a revolver cannon that we stuff in our updated A-10, or Picards’ ALX.. So my original idea of two seperate cannons (or maybe dual AP revolver cannons + 4-6 barrel HE rotary cannon) still potentially has a ton of value to provide. Additionally, in the updated F-16, or Picards’ FLX, we can use a squeezebore revolver cannon (or two) to get a massive advantage over all other modern fighters, using something around a 28mm/20mm cannon, or potentially even much smaller. The same gun can be put x2 on the A-1 Skyraider, giving it serious armour destroying capabilities, and the other two cannons can be made to shoot LV HE.

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       7. Riley, I think you may have misunderstood my proposal. The entire purpose of having two different guns is so that we never fire HV AP rounds and LV HE rounds from the same gun. That would make it impossible for the pilot to hit things, and requires differently designed guns anyway. I specifically stated that there will be a rotary cannon firing a mixture of low velocity HE/HEI/HEF rounds, and at least one revolver cannon firing super HV APCNR rounds. The pilot will choose between the two as to what he will be firing.

          When you say “a regular 30-35mm cannon with 40-50mm barrels”, I assume that you mean with 4-5 barrels, not to literally use barrels shorter than the rounds themselves. One of the main advantages of designing the round to be LV, or even ULV, such as <500m/s (which I think might be too slow), is that we're going to be using much shorter barrels. Since the barrels are shorter, they will also weigh correspondingly less, which means that it's not as urgent for us to reduce the amount of barrels at all costs. While there's a sweet spot, I think that rate of fire is so important here that there's no reason to skimp, so we might as well go for a 7 barrel gun here, with a rate of fire of 4000-6000 rpm. This is even more true for my gun, since the reduced velocity will necessarily affect the accuracy of the gun.

          Recoilless rifles are a very interesting idea. However, I was thinking about them and I'm not sure what they can do that can't be solved with a mixture of 127mm rockets and 70mm rockets. Secondly, the backblast from them is significant, so there are some practical issues with mounting them on a plane.

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       8. I’m convinced I’m up to speed with your proposal now, my apologies. The reason I waver on the idea of a smaller cannon for HE is that often times a single large explosion is more desirable than multiple small ones, I large warhead throws fragments further, and the larger shock wave has obivous advantages – consider the use of the large cannon for not only MBTs but also for bunker-busting and other things such as smoke laying, larger shell = more smoke.

          By “30-35mm cannon with 40-50mm barrel” I am refering to barrel changes to suit Super-40 and 50mm Supershot rounds, knecked up 30mm and 35mm respectively – the capacity for powder is propellant is expanded (especially in the APFSDS variant) and the projectile is of couse more volumous. Forgive my think out loud in my replies, I am very interested in finding a way to fire saboted projectiles to take advantage of these rounds. The cannon itself would be a single barrel, externally driven if possible but gas would suffice and would be MOTS – I don’t like the idea of >4 in any form of aircraft cannon. The larger the cannon the more accurate fire will matter to conserve the limited on board ammunition, and with that, rate of fire becomes less of an issue.

          My recoiless rifle proposal presented itself as a twin-boom aircraft with the rifles in said booms, venturi nozzle at the extreme rear and with the muzzle only barely breaching forward. The feed system was ultimately the let down, however I have a better idea now which focuses on a high-low pressure mechanism.

          You raise a good point regarding the benifits over unguided rockets, the reason I pick the cannon is for; lower cost ammunition, smaller ammunition, far more efficient use of propellant than rockets, internal mounting with far less drag, easier loading, and lower cost.

          Shoot me an email if you want to chat, I’m having issues with my comment notifications it seems: rileyamos0@gmail.com

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       9. I like the squeeze bore idea a lot, I had it in mind but gave up because of non-AP rounds, but the idea of AP only is intrueging. Again, keep me updated.

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       10. I think that discarding sabot might remain the best option if the technical problems could be solved.

           It is likely that if taper bore weapons were anywhere near as good as sabot, they would be used in modern MBTs.

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44. Advantages and disadvantages of RCLR vs Rockets:

    The problem that I see with RCLR is just that I’m not sure how we’re going to handle the backblast. This could amount to nothing, or it could be totally unworkable. All I could find are some forum posts that claim the English and Germans both tested these, with failure. That seems pretty reasonable to me, as the backblast is easily enough to shatter glass, it seems fairly scary to me to put one on an aircraft.

    If you could do it, the benefits would be significant. As you mentioned, replacing the fuel with gunpowder gives us significant weight savings. If you can place it inside the plane, then it would be much more aerodynamic as well. Personally, I can’t imagine that working unless you had the waste gases piped all the way to the very back of the plane, which seems impracticable. You could also maybe pipe them out the side, but that would require a second RCLR firing at the same time for balance reasons, and redirecting the gases gives us some recoil anyway. I couldn’t think of how you managed the internal venting, and when you place the RCLR on the wings you still deal with the backblast effect, which is a huge deal on the A-10 since the engines are behind the wings.

    There is a second issue which I largely agree with, which is that generally larger shells are worth it, and require a lower rate of fire to be effective. The main counter I have to that, is that I’ve never seen a high rate of fire autocannon that was more than 40mm, and we actually want a high ROF, and relatively low force, just for practical reasons, in order to reduce the amount of shaking induced in the plane. If it is possible to build a 105mm RCLR or LV Cannon, that fires >120 rpm, then that would be amazing for HE/HEI/HE-Frag. It’s actually even better than the simple size increase, as it becomes practical to put proximity fuzes on our HE-Frag shells, for even more efficient anti-personnel use in some situations. Having said that, the increased area damage from shrapnel that a proximity fuze is designed to give you (triggered upon distance from the ground) means that we can’t really use it to replace a gun.

    Also, although RCLR have great initial velocity compared to rockets, the velocity of them is still fairly low, and over a large enough distance the rocket ends up being superior. To give some real numbers, the US M40 106mm has a muzzle velocity of 503 m/s. This is actually somewhat high for RCLR, a lot of them that I saw online have muzzle velocities of less than 400 m/s. All of this makes sense, the disadvantage of allowing the explosion to travel out the back means that we lose a lot of additional propulsive force over a gun. In comparison, the muzzle velocity of a hydra 70mm rocket, is 700 m/s. The rocket is also going to have massively more firing range, with Wikipedia give an effective range of 8km, and a max range of 10.5km. If you wanted, you could increase the payload/weight ratio simply by removing fuel, and still have vastly superior velocity to a RCLR. On top of all that, the rocket exhaust is a pretty minimal concern, and the accuracy of rockets like the CRV7 is actually greater than the GAU-8, 3 milliradians vs 5. There is some sweet spot between payload and effective range, but RCLR are at the very opposite end of that, and rockets provide us more flexibility with respect to range.

    Finally, if it is absolutely necessary to have a giant HE explosion, good old fashioned dumb bombs are an option. As antiquated as they seem, bombs have the absolute best payload/weight ratio by far, having no propulsion themselves. So if absolute efficiency is what is required, then we would use bombs. If we’re not interested in pure efficiency, which I imagine we’re usually not for practical reasons, then we’re going to pick something else on the range of payload/weight in exchange for tactical/strategic use. Here’s basically the whole concept summed up:

    Bombs -> Great P/W, terrible accuracy-distance
    RCLR -> Good P/W, poor accuracy-distance
    Rockets -> Poor P/W, great accuracy-distance
    HE Rotary Cannon -> Good P/W, good accuracy-distance, fantastic ROF
    AP Revolver Cannon -> Specialized anti-armour.

    So if you can get a working RCLR onto an airplane that is definitely valuable. If not though, it’s not really such a crushing blow to us. The most important weapon I feel is obviously the gun, since it essentially peppers a very small area with frag grenades at 70-100 rounds per second. I’m actually doubtful that there’s much on the battlefield that can survive being targeted by 10 or so 40mm shells, and for the holdouts that’s why there’s an AP gun, rockets, and dumb bombs.

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    1. This comment was accidentally posted here. It was originally meant as a response to Riley.

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       1. Easier to reply if it’s seperate.

          I totally agree with everything you’ve said there, I’ll still comment on a few things:

          Recoilless rifles have been tested and from what limited information I can find, worked well enough (at least no catastrophic failures), the limiting factor seemed to be the single shot. As I mentioned my layout has the venturi nozzle mounted to the EXTREME rear of the empennage, a twin boom with a high mounted horizontal stabiliser (very similar to an OV-10). Assuming a blast of 45* to either side, there should be zero problems with it.

          https://out.reddit.com/t3_2fzfem?url=http%3A%2F%2Fi.imgur.com%2FIjhVN7f.jpg&token=AQAA81asWksFSemyDMCoCJKLNkWij9sQlMj5iS9ZaqdKvS_BQ7rM&app_name=reddit.com

          The rifle I am using as the basis is Sweden’s Pvpj 1110, a 90mm RCLR with a 650m/s minimum muzzle velocity. Rockets of course have the advantage of continuous burn, but a rocket assisted projectile is possible, although I don’t like the added complexity and cost. Supposedly 800mm RHA penetration can be achieved, suits me!

          My reasoning for cannons over rockets boils down to HEAT diamater, the best hope for destroying tanks will be in my opinion HEAT over kinetic for the weight and size allowed. A 70mm rocket isn’t going to be very useful in that regard, a 127mm rocket will be sufficient but at that point the weight and cost have skyrocketed to the point that a 90mm shell will be ten fold cheaper. The maximum kinetic power we can get would likely come from CRV7s with those penetrator flechettes, however the drawbacks occur. Upon this, only the CRV7 achieves an acceptable accuracy, all other unguided rockets start spinning outside the pod and tend to drift.

          Tapered bore cannons are tempting, keeping in mind however the stress placed on the barrel. Squeezing a steel skirt down on a projectile travelling extremely fast, and at a rate of 10 or 20 per second puts an incredible amount of strain on the cannon. Barrel life suffers drastically (500 rounds for the sPzB 41) and by virtue of the mechanics I would not like to be near it when it fails. Rifling is… complicated, you could have a fin stabilised projectile, however it would mean the projectile would have to be designed with exposed fins and not be squeezed down to more than the span of them. I’ve averaged a reduction of 28% in diameter for tapered bores, velocity increase over full caliber may be a similar figure.

          As I mentioned my sights have turned from recoiless rifle to high-low pressure cannons, which can be safer (no back blast), smaller (a huge reduction in propellant required as there is none wasted on countering the shell), lighter and cheaper, although we sacrifice velocity.

          Before looking into large cannons on aircraft I had considered 250lb iron bombs to be the bread and butter, and 80 class bombs are still a massive part of my thinkings, however they lack the standoff range of a cannon, and as you mentioned; the accuracy isn’t fantastic.

          That list you’ve made sums it all up, maybe there is no best choice. I’ll mention again, I agree with everything you’ve said, I only mean to spark discussion.

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       2. Well I suppose the major difference is that I believe that my AP revolver cannon would absolutely be able to destroy any MBT in the world. A 40/28mm squeezebore with a tungsten core would penetrate between 160-240mm of RHA, which would easily disable any MBT, and probably even outright penetrate through the top armour. The 25mm APDS round of the Bradley disabled the Abrams through friendly fire multiple times in ODS, so it’s just kind of ridiculous to think that a MBT would just shrug off a 40mm round. Personally, the only reason I even went for a 40/28mm cannon in the first place, is just that it is guaranteed to do the job. We can almost certainly get away with something much smaller.

          Secondly, there aren’t even that many MBT’s on the battlefield nowadays anyway. So if you’re expecting MBT’s, and for some strange reason the AP gun isn’t doing the job, then it really isn’t all that inconvenient to go for some 127mm rockets, which do still provide better range. Again, there’s no reason to expect that our AP guns won’t work, but even if they do, we still have a way of dealing with the MBT’s, to say nothing of the less heavily armoured fighting vehicles.

          No duplicate.

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       3. Having said that, the High-Low Pressure Cannon is extremely interesting. Reading about the weight savings from wikipedia, from my understanding we get essentially half the velocity, but at weight savings of potentially many multiples more than half. The only problem I have with the system is totally understanding it. If I am getting things correctly, based on the diagrams from Wikipedia, then we have a small inner core with holes that let the pressure of the initial explosion expand into the larger barrel, but there is a perfect seal on that larger barrel. I can’t be understanding that correctly, because in that scenario we’re not really saving any recoil that way. Alternatively, we have holes in the barrel itself, but a solid back plate, so we essentially get a muzzle break all through the barrel, at the expense of significant losses. I just can’t quite wrap my head around it.

          Anyway, mounting that on a plane would give us some value for sure. Definitely they would replace the RCLR’s, and would be an extremely useful option. Having said that, I still don’t think it’s a valid approach to hitting armoured targets. Tanks have a nasty habit of moving, and aircraft will always be at or beyond long-distance (for tanks) range when engaging them, so I don’t think there’s much value to be had there. However, I see this as being potentially extremely useful for anti-structure/building/demolitions work, essentially giving us an infantry gun to carry around with us when we feel like it.

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    2. The velocity loss is probably more of an issue than I am making it out to be, the saving grace may be the fact that velocity is what the cannon can produce + the speed of the aircraft at, say, 100m/s (360km/h). This of course applies to every single other cannon we can mull over.

       You’ve understood the concept correctly, as I’m sure you’ve read it’s the same system used in 40×46 rounds, the equivelant of kicking a ball versus pushing it. Have a look at the PAW 600 if you haven’t already.

       I’m really warming to the squeeze bore, I think that a 35-40mm cannon could be used conventionally, and then act as a squeeze bore with just a barrel swap. Barrels will need to be changed frequently anyway, might as well make it a feature! If you want to get fancy, a sensor fused flechette round could be used as an effective anti-UAV/helicopter weapon. My preference would be a conventionally rifled continous caliber barrel, with the last ≈750mm being tapered and smooth bore.

       I’m interested to know how you imagine the projectile?

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       1. Barrel wear is definitely an issue, which is why I was trying to get a smoothbore version with folding fins working, before largely giving up. Having said that, even the Germans eventually went for a straight barrel, with a tapered and removable adapter screwed onto the end. The adapter can be taken off whenever, and has to deal with the stresses of downsizing the bullet, as well as the absolute highest velocities. So I think we’re mostly in agreement here, although if I’m reading things correctly, I think you want the entire gun to be one piece. I think that’s a mistake, for practical reasons, due to the easier and cheaper maintenance of the adapter, rather than an entire barrel. Additionally, I’m not particularly worried about the barrel just exploding on us, since as the wear increases, we’re just going to see a decrease in the rifling. Finally, my bullet design is basically identical to the tungsten penetrator designs of the English and Germans when firing their APCNR rounds, which is to say, dense tungsten slug inside, wrapped in a thin soft-metal outside.

          I have been idling wondering about a smoothbore that is designed similar to torpedos or bombs, where the back cuts away and the fins are actually in line with the projectile itself. This totally solves the folding fin problem, but I’m not even close to convinced that we can get enough spin imparted by those fins. Since the soft shell around the metal will necessarily have some thickness, you can easily do a sort of wasp-waist design, where the second collapsible ring has just penetrator behind it, and the find start to go out from there, but whether that’s enough is unclear to me. I have also been toying around with cutting slanted holes in the projectiles second ring, which cause the gasses to rotate the projectile while still in the barrel, but that could cause problems with warping of the ring, and might not be enough rotation anyway. There’s only so much I can do without access to prototypes, or aerodynamic modelling software at the very least.

          Not particularly sold on the sensor fuzed flechette round. I’m assuming you are attaching a proximity fuze to the round, and triggering it above ground? 40mm is probably the absolute smallest possible shell that makes sense to use in that respect, and I can foresee a lot of problems with collateral damage using proximity fuzes in that way. It’s definitely something that we would love to magic onto the shells when convenient, but I don’t see a reasonable way to have the proximity fuze attached and easily load the shell. For practical reasons we don’t want to just mix them in with the rest of the ammunition, and we also want to be able to arm them or not arm them. For these reasons, this is why I am a huge fan of proximity fuzes for bombs and rockets, but much less of a fan for shells from a rotary cannon. It’s not that it isn’t a great option, it’s just that it has some clear drawbacks that don’t exist for bombs and rockets, and in my proposal we would be developing those bombs and rockets for that role. If all we had was the gun I would be a big fan.

          As far as utility against UAV’s, helicopters, the squeezebore HV AP gun I imagine would work fantastically well against them. The initial impetus for this concept wasn’t made for my CAS plane, but rather for the gun on Picard’s FLX. Personally, I actually think that a CAS plane like my updated A-10, or Picards ALX, is actually the best way to deal with helicopter/UAV cleanup, but in that role I think that high velocity is a lot more useful than low velocity sensor fuzed frag rounds. Imagine trying to hit something with a 1400m/s AP round with great aerodynamic performance, versus a 600m/s HE-Frag round with a proximity fuze. Seems to me that the AP round is going to get the job done better and safer.

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       2. I’ve drawn up a thought for fin stabilisation, really nothing new: https://imgur.com/a/kQbCk

          Removable adapter is probably the way too go, the only reason I was thinking of a dedicated barrel is because I assume a uniform taper along the entire barrel would be better than a sharp taper at the end. The stabilisation issue can therefore just be solved by having a rifled barrel and a smooth taper adapter.

          Sensor fused flechette is more of me thinking allowed, more as a comment on the merits of a full caliber option for different payloads.

          A KE projectile will of course be good for Helos/UAVs, assuming hits are made. The 40x364mm has taken down it’s fair share of aircraft without the need for a direct hit, you could well be correct though.

          Exactly what cartridge are you basing your idea on? I have opted for 40×364 as mentioned, from a resurrected and modified Bushmaster IV which I will draw up at some point.

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    3. Large calibre cannons on aircraft can be replaced by recoilless rifles, or you can have a dual low-calibre (30 mm) / large-calibre (75 – 105 mm) mount, which IIRC was done in World War 2.

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45. Been a while since I last commented, how is everyone doing?

    On that note, I think that there are a few other considerations:

    If we are going to be using a taper bore (or squeeze bore), then we will need the projectile itself to be tungsten. The WW2 era guns had powder that weighed almost as much as the projectile. There were also issues with accuracy fall off that will have to be addressed with range.
    I will have to find the thread on recoil less rifles, but we did find some engineering challenges. We never concluded if they were insurmountable or not.
    I am not sold on the GAU family of gattling guns. They take 0.5 to 1 second to spin up to maximum fire. Revolver will be needed or a gas operated gattling gun, which is what the Russians use.

    That leaves us with a weapon with the following:

    Tungsten barreled high velocity squeeze bore
    Very fast spin up time so either 2 revolvers or a gas operated gattling gun
    At least 30 mm to destroy enemy armor

    I think that rockets could be used as a secondary wing or fuselage mounted weapon as a supplement to the gun. Possibly a CRV 7 like rocket, for engaging enemy vehicles and buildings.

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    1. Too busy to write much on blog, I haven’t posted anything even in online newspapers for a while, let alone on a blog.

       And yeah, good ideas.

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    2. Yes, definitely tungsten.
       Have to find that thread myself, but I agree that there do appear to be some insurmountable challenges. More than that, I think I raised some good points questioning the point of recoilless rifles anyway, since large diameter weapons can just use fin stabilized rockets, without the terrible backblast issues.
       We would need to have actual field experience, or at least talk to existing A-10 pilots to plot the best course here. I myself favour revolver cannon for armour penetration, while I believe that a rotary cannon is best for soft targets with explosive rounds.

       However, one of the reasons I never really followed up on this much is that we can’t proceed in the absence of actual pilots and engineers. There are lots of valid concepts that I just can’t move past conception. For example, I was thinking of getting rid of the HV armour piercing revolver cannon(s), and instead going with a lower velocity Revolver Cannon, like the GAU-8, but with drastic weight savings due to the decreased muzzle velocity. The rounds would be a combination of HESH, HE, HEI, and HE-FRAG, with the precise loadout depending on the expected conditions. However, to go further with that design I would need to:

       1) Talk with a bunch of A-10 pilots to figure out:
       – The order of importance of the attributes of the gun, Fire Rate, Startup Time, Muzzle Velocity, Total Magazine Capacity, Accuracy, Armour Penetration, Explosive Effects, etcetera

       2) Talk with a gun designer/manufacturer to figure out:
       – Weight savings from barrel shortening/round composition change, Magazine Design/Capacity, Lifetime effects due to lower muzzle velocity, etcetera

       3) Talk with an Aeronautical Engineer to figure out:
       – How to fit the new gun inside the plane, Where to put the Magazine, What to do with the extra capacity (shorten plane, put other things there, etc), etcetera

       4) Talk with a experienced mechanic to figure out:
       – How to make changing the gun easier/cheaper, etcetera

       I’m sure I’ve missed a few people and that’s not including politicians. It could be that the pilots are absolutely thrilled to have something like a 750m/s 35mm cannon with a lower fire rate, or it could be that they absolutely want every m/s that they can get for valid reasons.

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       1. Further musings on this topic:

          An undoubtedly catastrophic idea I had was some kind of plate projected in front of the cannon muzzle which would have a hole to allow the projectile to fly through but would capture and deflect the sabot, but it would have to be a hell of a structure

          In my current CAS aircraft that I will hopefully one day get around to writing about, mounts a single M61 rotary cannon with 550 rounds. The crux of the aircraft is modular stores in two semi-recessed pods, these pods have effectively unlimited configurations. Housed what we have dubbed “The Brrrrt Box” is an Oerlikon KCA with a drum feed – with two of these mounted we have a respectable 2,700rpm of redundant 30mm slinging.

          The pod itself is a hold over from the sister project of a light stealth aircraft, the pods are angular and sized to house a 2000lb JDAM.

          We have laundry list of pod configurations such as:

          Rotary 70mm or 127mm rocket launcher
          Rotary 152mm HV rockets
          Ferry fuel tank
          Conformal AMRAAM (2), AMRAAM-ER (1) and ASRAAM (3) launchers

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46. Turns out I was wrong about hp to thrust conversion.

    Luckily for me, turns out that some people have actually gone ahead and tested how much thrust a prop engine will give you, when actually installed into an aircraft.

    https://flycorvair.net/2013/12/23/thrust-testing-85-and-100-hp-engines/

    Turns out that one HP is going to translate into around 3-3.5 lbs of thrust. I’m glad I finally found some numbers. While there is no real way to empirically test the thrust generated at any given speed and altitude, theoretically the thrust generated drops off on an exponential curve, where the “knee” of the curve seems to hit at around 812kmph. I finally found a graph of what I was looking for here.

    https://cafe.foundation/blog/a-different-kind-of-hybrid/

    So let’s calculate how much thrust that my “Steroid Horsie” is actually producing. Well, at reasonable, not too hot, temperatures, then at sea level on takeoff the Steroid Horsie is, with 2x 1980HP (let’s say 2000hp for ease) PT6 engines, produces somewhere between 12,000 and 15,000 lbs of thrust. At 400 kmph, we’re still going to be getting 90% of that thrust, which works out to between 10,800 lbs and 13,500 lbs of thrust. Considering that the airplane weighs, at combat weight, around 9,000 lbs, and we have quite possibly the most overpowered airplane in existance. I think that we’re probably sacrificing too much for the raw thrust. If we go down to the 1,100 hp version of the engine, then we’re still getting 6,600 to 7,700 lbs of thrust on takeoff and 90% of that in flight. All for much more reasonable fuel consumption during loiter and cruise.

    The point is that I have now done a complete 180 on my original belief that a turbofan would be required in order to generate the thrust we needed for our airplane. I now see no reason at all to have one. Turns out, the only reason that the A-10 has a turbofan engine is because the TF34 was developed for the S3 Viking, so they were forced to add it on to the A-10. It’s not like the A-10 ever actually goes fast enough to justify the slight decrease in drag that comes with a turbofan. If we really wanted to upgrade the A-10, we could just stick some PW127 engines on there, producing 2,750 hp, or around 8,250 lbs of thrust, along with drastically reduced overall weight and we have a winner.

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    1. Which brings me to my next comment, which is that ultimately, the A-10 actually kind of sucks in some important ways. The A-10 is like some troop transport helicopter from 1965, and the soldiers love it to death, but the USAF wants to kill it because it’s an aircraft that reminds them of the absurdity of victory through airpower alone. If transport helicopters were the domain of the USAF you can bet they would be killing the aircraft every chance they get. Arguments in favour of the A-10 are basically arguments in favour of the mission the A-10 does, just like arguments in favour of keeping our theoretical old transport helicopter are arguments in favour of the helicopters mission rather than the actual specifics of that helicopter.

       Going forward with the mission of CAS, I think we can reasonably base our designs on one of three American airplanes, the A-1, the OV-10, or the A-10. All three of these designs have served with distinction, and all three have some advantages over the other two. I feel that we can rule the A-1 out fairly quickly, since it is the worst gun platform of the three. As an aside, I would still be making something like the A-1 to serve as a naval strike aircraft, where raw payload and range matter the most.

       Taking the designs as they are, the OV-10 has clear and obvious advantages in terms of overall size and weight, while the A-10 has been designed for a cannon similar to what we’re putting on our ALX. The OV-10 also wastes weight and volume on a second seat as well as the cargo bay. However, I absolutely love the high wing design, especially with sponsons added. The sponsons I feel are a fantastic touch, and the perfect place for our four 7.62mm machine guns. I do also love the A-10’s semi-retractable landing gear design, as well as hiding the engines behind the wing, which I feel is in some ways the best armour.

       Ultimately you can make arguments for either one. I personally am going for something in the style of the OV-10 Bronco or the Convair Charger over something in the style of the A-10. TBH, I’m arguing for that mostly because I just simply don’t understand why the A-10 is so damn heavy, and I can more easily extrapolate the weight of my modified Bronco, which feels a lot less handwavy then saying “oh and now the A-10 weighs half as much because we changed the design”.

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       1. Alright, so what is our Steroid Athlete going to look like? As a brief overview, take the equivalent of the titanium bathtub from the A-10, using modern composite armour. Create a version of the Gau8 that runs on the Gast Principle for weight savings. Add a laser to one of the Broncos Sponsons so it can fire laser guided rockets. Get rid of the cargo bay on the OV10 to save weight, and the second seat for the same reason. Keep the 4×7.62mm machine guns on the Bronco, since that solves the A10’s longstanding problem of not being able to fire in ultra close (<20m) situations without serious risk of friendly fire. Then up engine the Bronco so it has two 1600hp PT6 engines.

          Remove the cargo bay from the Bronco. Also remove the second seat, although we might have a version with a second seat. Get rid of the asinine requirement to have such absurdly strong landing gear, and get rid of or maximally shrink the 1000 lbs of electronics "required" to do FAC. According to Bill Beckett, one of the two creators of the Bronco, those two changes added 1,000 lbs each of unnecessary weight. Getting rid of those two drops our empty weight from 6,800 lbs to 4,800 lbs. Get rid of the second seat and cargo bay and I believe we could save another 1,000 lbs. Let's say, conservatively, that we're down to 4,000 lbs, on our very light CAS airplane.

          Now we go and add weight back into the airplane. First of all, let's steal the cockpit bathtub idea from the A-10. 1,200 lbs would be added, however, agreeing with Pierre Sprey here, there has been a lot of work done on armour since the late 1960's. Since we don't care at all about HEAT rounds, we need to be armoured against direct hits and airburst with AAA. The current bathtub is armoured against direct hits from .50 cals, and airburst up to 37mm. I think those are reasonable targets. We could probably just steal an idea from back around the A-10's development and go with perforated steel armour, which is basically a steel plate filled with holes, which are themselves filled with ceramic inserts. Back that up with a spall liner, and we've got our new armoured bathtub. Conservatively, we can probably do this for 1,000 lbs of weight, pushing us up back around 5,000 lbs.

          Alright, now we have to add the gun. First of all, one of the biggest problems with the A-10 is the lack of a small machine gun or two. This prevents it from truly being used in ultra close contact with troops. If I'm 5m away from the enemy and someone fires a 30mm HEI shell with a lethal radius of 15m at them, even if they hit them perfectly there's a very high chance of me dying as well. This problem can be solved simply by the addition of 2 or 4 7.62mm machine guns, like the Bronco already has, and is probably the only head scratching design decision on the A-10. However, giving us 4×7.62mm guns, with an appropriate ammunition load, let's just keep the Bronco's 500 rounds, also frees us up to remove stored ammunition for our 30mm cannon.

          I think you've stated it previously, but the rotary cannon on the A-10 probably is optimistic. Going by Hans Rudel's experience with super dense AAA defences, snapshots are all we're gonna get. Pierre Sprey also came to this conclusion, and I think it's reasonable. I'm very skeptical of a single barrel revolver cannon truly handling the stresses of firing at a very high fire rate, so that's where the Gast Gun comes in. An American answer to the Russian GSH-30-2 autocannon, which fires at a selectable rate between 1000-3000 RPM should give us plenty of fire rate. Considering the higher velocity, and thus higher barrel wear of our 30mm, let's stay on the safe side and say that we are aiming for just 1200 RPM cannon, 600 RPM for each barrel. That still gives us a fire rate of 20 rounds per second. Since we actually get that immediately, due to the linear action, a half second trigger pull still gives us 10 rounds fired. I don't really believe that if you fight a serious enemy you're going to get many chances for shots longer than a second, maybe even longer than half a second, so let's use that as the benchmark. If we want 25 full second attack passes, then we are going to need 500 onboard rounds. Frankly, that might be overkill, and we could very well adjust that downwards if we're having issues with our design and fitting all the ammunition on board. Personally I feel that anything below 100 rounds is probably unacceptable, with 250 rounds probably being a decent serious amount.

          The GAU-8 API round weighs 1.62 lbs and the HEI round weighs 1.48 lbs. Call it 1.5 lbs for both of them. Our weight savings going to a Gast Gun are, based on the Russian GSH-30-2 as an example, going to be around 300 lbs. Going from the current loadout of 1,150 rounds down to 250 rounds saves us 900 rounds. At 1.5 lbs per round that's a weight savings of 1,350 lbs. So we've already saved about 1,700 lbs off of the 4,000 lbs total gun system. I can't quantify how much weight we can save with the drum and the complicated dual hydraulic system deleted, but I would be shocked if we couldn't knock this down to well under 1,500 lbs for the total gun system. However, I'm going to again be fairly conservative, and say that the cannon, with all the ammunition on board, and with recoil dampers installed, adds another 2,000 lbs of weight. Now we've been brought up to around 7,000 lbs.

          We can keep the hardpoints at the same number and strength as before, although I would like to add that I would cringe if people kept hanging rocket pods off the plane. I mean, why bother with retractable landing gear if you're just going to hand excessively draggy things off the airplane. I do believe in putting a laser pointer on one of the sponsons, and adding wingtip rails capable of supporting the 79.5 lbs of a Zuni rocket, which would have a laser finder at the top. Let's say 100 lbs, just to make the math easy, and we have a rocket capable of doing a lot of the occasional utility work without being an aerodynamic horror show. Adding a FLIR in the nose above the cannon makes a lot of sense. We might want to add some UV MAWS to the tail potentially. None of these things really add too much weight or drag.

          So there we have it, a 7,000 lbs CAS airplane when empty + ammunition. An absolute beast. And what luck with the numbers, if we give this thing 3,000 lbs of onboard fuel we're at a fuel fraction of 30%, which, frankly, might be excessive, but would at least guarantee great endurance and range. So now we have an airplane that weighs 10,000 lbs on takeoff and 8,500 lbs at 50% fuel. The remaining question we have to ask ourselves is how much engine do we want on this thing, bearing in mind the increased fuel consumption even at idle for a large engine. All thrust values below are for takeoff at sea level. For thrust at 5,000 ft and 300 kmph, just multiply by 0.8 to get a ballpark estimate. Also, a value of 3x was chosen, to ensure a conservative estimate of thrust. Again, empirically 3-3.5x lbs of thrust to hp has been proven.

          Looking at the range of possible engines we have two 600 hp P&W engines. That's gonna get us around 3,600 lbs of thrust. Considering that the combat weight of the Steroid Athlete is about 8,500 lbs, frankly that may well be good enough. However, early users of the 750hp Bronco complained about it being underpowered in the mountains. I heard a conflicting report reading Marshal Harrison's excellent book "A Lonely Kind of War" where he complained occasionally about the low cruise speed, mainly because of the falsely advertised 250 kn cruise speed, which was just a complete joke. I also heard, although I can't remember where, another former OV-10 pilot say that the airplane had plenty of power until they started hanging "all the junk" off the airplane. This strikes me as being more accurate. I looked at Wikipedia and the fueled up weight was almost exactly 10,000 lbs, plus the weight of whatever they wanted to hang on the sponsons. We have to keep in mind that net thrust is a combination of thrust minus drag for any given speed and altitude, and while it's not a fighter plane, excess drag must be avoided on the airplane.

          Before we go any further, it's worth mentioning that A-10 pilots complain about not having enough power, which is basically another way of stating not having enough (Thrust-Drag)/Weight. I've said before that the A-10 needs to go on a diet, but, according to Wikipedia, the A-10 has about a 0.42 Thrust/Weight ratio. If that's considered underpowered by A-10 pilots, then we should probably be aiming for that as a baseline minimum. 3,600 lbs of thrust generated from the two 600 hp engines gives us 0.36 thrust/weight ratio, which is probably a bit unreasonably low. For comparison, the old OV-10 bronco, with it's 750 hp engines would be generating 4500 lbs of thrust, at, say, 13,000 lbs, which is a thrust/weight ratio of 0.35, and was considered underpowered.

          If we go at the other extreme, two 2000 hp engines is going to give us 12,000 lbs of thrust. I'm just going to rule that out immediately. While it sounds cool to have a CAS airplane that could theoretically take off vertically the fuel guzzling that thing would do just to stay in the air is painful to think of. Although a 1.2 Thrust/Weight ratio is fun to think about.

          For something in the middle, two 1,100 hp engines is going to give us 6,600 lbs of thrust. That's a 0.66 thrust/weight ratio, which is probably very solid. If we go up to 1600 hp engines, then we're getting 9,600 lbs of thrust, for 0.96 Thrust/Weight. Probably one of these two choices is the best or something just in the middle. To be honest, I lean towards the less sexy 1,100 hp engines for a few reasons. First of all, I've been keeping the weight the same, but we're actually looking at a range from 325 lbs to 665 lbs going from 550hp to 1,970 within the PT-6T-68, which it turns out is actually a turboshaft. Sticking with the usable engines, the PT6A-68B used in the Pilatus PC-21 weighs 575 lbs and generates 1,600 hp. Actually, I guess the weight difference is really not all that meaningful anyway. Turboprops really are efficient in terms of power/weight ratio. Alright now I'm leaning towards actually going with the 1,600 hp engines, for 9,600 lbs of thrust. We would have to calculate how much much the increased fuel burn cuts into endurance and range, with endurance being somewhat more important. Gas turbines really don't power down all that efficiently, but I think it might be worth it on the Steroid Athlete. We could also potentially be limited by safety should one engine go out. We don't want so much power that the plane flips over, but I can't quantify that danger.

          So anyway, that's what I've come up with. What do you think?

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       2. Nice. I quite like it.

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       3. Great layout, why go for the Bronco over a Pucara as your base?

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       4. @Picard578

          Thank you. I think it’s arguably fuel efficient enough to be used as a general purpose scout aircraft as well, although very big nations that can afford more specialization may go a different route.

          @Riley-Amos

          A few different reasons. Firstly, the Pucara is about twice as big as the OV-10 Bronco, or what it was before the USAF and USN added 2,000+ lbs to the airplane, according to Bill Beckett, one of the main two men responsible for the plane. Secondly, I simply lack familiarity with the Pucara, so it’s harder to come up with additions. The use of cutouts on the side for the placement of machine guns is not a bad idea, and I have a lot of respect for the Pucara. They clearly had the same idea that I had with regards to the multiple gun types, although sticking a 30mm out the nose would definitely result in some redesign of the landing gear.

          I feel like the high wing design of the Bronco makes a lot of sense for a few reasons.

          1) With the pilot forward of the wing you can still see behind and above you fairly well. More importantly, you can perfectly see behind and below, if flying straight and level. However, if you need to roll into something and turn, then there could be some situations where the wing blocks your view, but with the wing back, this should be less of an issue. We can justify pushing the wing back in our design, since we need space to house the gun.

          2) The wing mounted engines also have more ground clearance with a high wing, which allows us to use larger propellers for the same clearance, or shorter, sturdier landing gear. Some combination of both would be used. The air intake is also further from the ground, which is a practical concern considering the dusty, muddy areas this trucker is going to land.

          3) High wing also lets us “cheat” the internal space and add Bronco-style sponsons, which we’re using for the M60 machine guns, as well as the laser pod. This essentially gives us more internal volume for munitions, can be custom designed, and provides a small amount of lift, partially paying for itself. Drag is not much of a concern for the airplane, so it’s not as horrific as a sponson on a fighter would be. The guns in the sponsons are also extremely accessible to the aircrew, which can only be a good thing.

          Definitely, using the Pucara as a base is extremely interesting and justifiable. However, if I was using the Pucara I would ABSOLUTELY use fixed landing gear. The only reason I went with retractable for the Bronco is because the twin boom design makes it cost very little for the retractable gear. If using the Pucara, the extra weight, fragility, and internal volume of retractable gear would, in my opinion, absolutely not be worth it. I don’t think it’s possible to have a centerline gun in the Pucara with retractable gear, so that would be one of the first things to go.

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       5. I’ll just comment here that I prefer low-wing designs such as A-10 for multiple reasons:
          1) they allow for much wider landing gear, thus allowing superior rough field operations
          2) lower wing position should also make rearmament easier – an important consideration for rough field air bases
          3) low wing also helps – to an extent – protect the engine from weapons fire and debris, should you use A-10s turbofan positioning

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       6. @Picard578

          I had another comment above where I discussed some benefits, however, I don’t feel like low wing provides quite the benefit that you think.

          1) This is true for fixed landing gear only. However, I’m coming to the belief that fixed landing gear is simply the right decision for CAS airplanes anyway, so low wing may well be much better in this regard. You could mount the landing gear at the bottom of the engine, sort of like a fixed version of the Bronco’s retractable gear, but that’s not be ideal, and it needs to be longer anyway. I wonder if you could mount these on the sponsons, but that might be trading one problem for another, in terms of the stress on the sponson.

          2) My vision does not have a lot of wing mounted armaments in the first place. However, to the extent that these are on the plane, it’s much easier to deal with if the wing is high versus low, unless the landing gear is comically long.

          3) I thought about this, and considered the A-10’s design much better in that sense. However, you also need the extra weight of the engine pylon, and I was basing my design mostly on the Bronco.

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       7. 1) Yeah, I consider A-10s landing gear positioning pretty much ideal for a CAS fighter.
          2) Not really. Unless said bombs are comically large, you only need to place them below the wing and then “rapple” them up. Much less work if wing is low, as there is less distance to cover.
          3) True. You also have the extra weight for engine armour. Though the fact that the engine is away from anything else critical somewhat compensated for that.

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       8. One issue is that the second person might be a benefit. So in that regard, the OV-10 might not be a bad idea after all.

          There were complaints about pilot workload with a single seat aircraft. For this reason, Picard also added a second seat for his CAS proposals.

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47. 1) A-10 probably does have the best landing gear design. Gets most of the benefits of retractable, still gets some benefits as if it was fixed. Still, even the A-10 is so slow that I still think non-retractable gear may not be worth it. Again, low wing would be better for this.

    2) I think you’re forgetting the irritation with physically getting underneath the wing in the first place. High-wing airplanes can just be walked under, so you have to hoist munitions higher, but you don’t have to break your damn back in the first place. Now some airplanes are so damn big that even low wings are almost six feet off the ground, but I don’t think either of us want an airplane that enormous.

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    1. Ultimately we should be able to make a reasonably well quantified guess as to the survivability of the A-10 pylon mounted engine design versus the OV-10 Bronco style wing mounted engine design in terms of extra losses per sortie. We should also be able to quantify the loss in weight, and the minor loss in thrust due to the more off center thrust, which requires some angling to compensate.

       The increased stability of wider landing gear mounted to the wing can also be quantified, versus something like the landing gear of the DHC-6 Beaver. The increased weight of retractable gear, as well as the reduced drag for any given speed should also be calculated. Finally, there are some practical design decisions that may require one or the other, such as fixed landing gear getting in the way of bomb dropping, or a retractable nose gear taking up space for the centerline cannon. Those design decisions actually have to be solved first, because we might find that fixed bicycle gear is the way to go, which necessitates a traditional fuselage, unlike the OV-10’s twin boom design.

       However, the most important criteria to design to, within reason, must be the visibility afforded to the pilot, and not in a vague sense, but specifically that which enables the pilot to do his job most effectively. For a high wing airplane, the pilot absolutely must be well in front of the wing, or I believe it would be unworkable, since he’s going to have to look up and back when coming around to attack things, which the wing will obscure. For low wing airplanes, the wings should also be as far back as possible. We have a disadvantage when flying straight and level, but we get a similar advantage when actually turning towards our objective, since the wing now only obscures, pretending a true 90* roll, ground well behind us, and a small amount at that. Paper designs must be made. Preferably, lots of prototypes would actually be flown and compete against each other.

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       1. Yes, visibility I think is the main reason why I went with low-wing design for my OLX. Wing positioning does not impact only landing gear, it also impacts fuselage design, and none of the high-wing aircraft I know of has very good rear and side visibility. Which is a problem.

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    2. 1) Yeah.

       2) That I think would also depend on the length of landing gear. If long enough, it wouldn’t matter, but I don’t think that would be practical for a CAS fighter.

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       1. One thing I have completely forgotten to mention. If we want this airplane to be used in snowy areas, or land on water, we’re going to need skis or floats. Additionally, due to the very high weight of this airplane relative to bush planes (10,000 lbs vs < 2,000 lbs), we are going to need enormous tires in order not to sink into any muddy ground, just like a land vehicle. That, or potentially tracks. Low pressure tires would need to be actually tested versus tracks, and might be good enough, but my vision is something that can truly land anywhere. I mean, we can pick our spot within a few meters of course, but any clearing should do.

          When you're attaching anything to the landing gear wheels, or even just using giant wheels, then you definitely can't retract the gear. That means that you're paying the price in terms of weight and volume and getting absolutely nothing in return.

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       2. It’s also a safety feature, since we might need to land immediately and unexpectedly for many reasons.

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       3. Low pressure tires would be enough for smaller fighters, tracks IIRC were only used for large dirt-strip cargo aircraft. As for floats, I was thinking whether drop tanks could be used as such in emergency. It would require them to be fastened rather securely.

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