Defense Issues

Military and general security

A-10 Thunderbolt survivability design

Posted by Picard578 on December 11, 2016

When the A-10 was about to be introduced, USAF leadership used the exact same arguments to prevent that as they are using now in an effort to kill it. They saw merely a clunker that flew at 300 knots or less, an anachronistic dud unfit to operate on the modern battlefield where it was to kill Russian tanks. In fact, the A-10 would never had been introduced if the USAF was not engaged in the budgetary battle against the US Army. Army was about to introduce the new attack helicopter, the Cheyenne. Cheyenne was a compound helicopter, designed to overcome the inability of normal helicopters to achieve higher speeds when necessary, and its high price would see financial resources redirected away from the US Air Force and into the Army’s purse. USAF would have none of it, and it decided to finally take responsibility for the close air support mission it was supposed to do anyway, and so introduced the A-10. Technical requirements were outlined mainly by Pierre Sprey after talks with surviving US and German pilots who carried out close air support in World War II and the Vietnam war, while the overall effort was directed by the Colonel Avery Kay. More heavily armed, survivable and less expensive, A-10 easily killed off the Cheyenne, and the USAF never placed any orders beyond the first batch. In fact, the A-10 was the first and the last US fighter designed for close air support.

Before being finally accepted into service, A-10 had to pass one final test against A-7 Corsair II. Tests, carried out during April and May of 1974., had shown that the A-10 is far superior to Corsair II in carrying out the Close Air Support mission, particularly in low-visibility conditions. Testing of GAU-8/A Avenger cannon was finished by September, and in October, testing of TF-34-100 turbofan engine was likewise done. First preserial production A-10A flew on 15th February 1975., and second on 26th April, after which two prototype YA-10A were retired. It was noticed that A-10A was slightly overweight, but this was deemed not to degrade performance by an unacceptable amount. First serial production A-10A flew on 21st October 1975., and was delivered to USAF on 5th December 1975.

Primary goal of design was high survivability in constested airspace. Analysis of air operations in Vietnam and Arab-Israeli wars has revealed that 62% of losses of single-engined aircraft was caused by fuel fire, 18% was caused by the pilot being disabled, 10% by damage to control surafces, 7% by engine loss and 3% by structural damage (further reading on topic of single vs twin engined aircraft here). Primary danger for the new attack aircraft was considered to be fire by antiaircraft guns up to 57 mm caliber, so all A-10s systems were designed to withstand a single direct hit by a shell of that caliber. Light ground-to-air missile systems (MANPADS) were not considered a significant danger, whereas defenses against SA-6 were primarily active jamming systems, as armor protection against missiles would degrade performance too much.

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Aircraft hull is of a half-monocoque structure, and is made from aluminum legures 7075 and 2024, known for their resistance to corrosion and stresses. Hull construction contains four longerons, multiple frames, while aircraft skin is riveted. A-10s design allows the interchangeability of components mounted on each side of the hull (vertical stabilizers, main wheels, hull panels, weapons hardpoints) which simplifies maintenance and reduces aircraft price. Pilot is surrounded by a titanium bathtub with plate thickness of 12,7 to 38,1 mm, whose sides also serve as parts of the airframe. Side panels of the tub are designed to withstand a direct hit by an armor piercing incendiary projectiles up to 23 mm in caliber. Bathtub weights 544 kg, which is 47,1% of 1.023 kg allocated to armored protection of the A-10. Additional 37,4% goes for protection of fuel systems, 9,7% for protection of 30 mm ammunition drum, and remainder for other components. Windshield is made out of bulletproof glass and can withstand hits from ammunition up to 23 mm in caliber.

Flight control is done by a double hyraulic systems. Unlike the F-105 Thunderchief, whose dual systems were right next to each other and so would get destroyed by a single hit, A-10s systems are spaced from each other and protected with armored plating. If both are destroyed, a portion of flight surfaces can be controlled manually. Special attention was given to fuel systems. Due to A-10s large wing surface, wings were made dry with the exception of small inner section up to the wheel. Main fuel tanks are located inside the main hull. All fuel tanks are self-sealing, and filled with porous foam, to stop the fuel leaks. Individual fuel tanks as well as the fuel tank section itself are sealed off from each other and from other systems by fireproof panels. Self-sealing fuel lines are fitted so that they pass through the fuel tanks. In the worst-case scenario, main fuel tanks can be isolated from the rest of the aircraft, in which case two small fuel tanks located between engines are used for fuel supply, allowing a range of 370 km to return to base.

Forward part of the aircraft is designed around the GAU-8/A gun and 30 mm amunition drum. Engines are mounted in armored gondolas on the aft part of the hull. This engine configuration was chosen for several reasons. It allowed simpler construction and access to the engines, allowed air intakes to be high above the ground so as to avoid ingesting debris; taking out one engine will not take out both; infrared signature of the engine exhaust is reduced; engines are separated from the fuel; engines can keep working while the aircraft is being rearmed.

Wings are straight and thick, optimized for maneuverability at low speeds and altitudes and generating lift during takeoff and landing. Low position also allows quick rearmament, as well as carriage of heavy weapons near the centre of the aircraft, resulting in reduced inertion during the roll. Wing construction has three wing spars, and outer wing has a dihedral of seven degrees. Wings have both slats and flaperons; slats were mounted after testing revealed negative interaction between the wing and the engine at high angles of attack (stall that developed at mid-wing would stop the air flow into the engine, leading to compressor stall). Ailerons on outer wing edges consist of two sections which can separate and serve as air brakes. All control surfaces are hydraulically driven. Wing tips are drooped to reduce vortex flows and improve aileron effectiveness at slow speeds. Plating of the lower portion of the wing had to be strenghtened due to cracks which appeared during the low-level flight in Europe’s turbulent atmosphere.

Main wheels of undercarriage retract into small aerodynamically shaped bays located on the lower inner section of the each wing. About half of the wheel protrudes when the undercarriage is fully retracted, allowing belly landings with minimal damage to the aircraft. Nose wheel had, due to the gun location, to be moved to the right. All three wheels retract forward, allowing air current and gravitation alone to deploy them should the hydraulic system fail; if this does not happen, aircraft can still belly land as described. Wheels are widely separated, making takeoff and landing from provisional airstrips easier.

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Twin tail surfaces of the A-10 hide the engine exhaust from ground-based IR sensors, as well as – along with the hull and main wings – protecting them from weapons fire from the ground. A-10 is also equipped with an auxilliary power unit which provides power for the engine start. Electrical systems consist of two 30/40 kVa 115/200 V alternating current generators, batteries and converters. Climatisation system uses the engine compressor air for purposes of pressurizing cockpit and pilot’s G suit, defrosting the canopy, fuel transfer, cleaning of fuel lines. Propulsion group consists of two turbofan TF34-GE-100 engines, originally developed for the S-3A Viking aircraft. All main components of the engine can be removed without removal of auxilliary ones, and compressor blades can be removed individually without the need to take apart the entire engine. TF-34 has shown itself to be resistant to use in sand conditions, as well as to bird ingestion.

Thanks to its construction, A-10 can get back to the base without half a wing, half a tail, a single engine, with complete hydraulics failure, or with several of the listed damages at the same time. During the static testing of aircraft’s construction, a sections of aircraft fuselage and wing – complete with full fuel tanks – were simply riddles with fire from a Russian 23 mm anti-air gun, using both armor-piercing and high-explosive incendiary ammunition. Around 430 shots were fired at the cockpit, 250 into fuel tanks and 60 into ammunition drum. Additional 108 pieces of various calibres were fired into front canopy panel. Testing has revealed that the area in which a single 23 mm shot was lethal was equivalent to 1/10th of the area on a smaller, unprotected aircraft. Foam in fuel tanks has also demonstrated excellent ability to stop any fuel leaks.

Actual live combat has revealed A-10s ability to survive hits from larger shells of 57 mm in caliber, as well as MANPADS and SAMs, much of the time. In one incident A-10 got hit by four 57 mm shells, including one below the cockpit, but the aircraft made it back and the pilot was unharmed.

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One almost always underapriciated aspect of aircraft survivability – especially by stealth proponents – is aircraft’s on-ground survivability. Conventional air bases are huge built-up areas, easily detected, identified and attacked. Even if the aircraft survive – and even with armoured shelters, there is no guarantee of that – cratering of the asphalt / concrete air strip will place aircraft at the base out of the action for the time being. This is doubly true for stealth aircraft, which require specialized controlled atmosphere hangars for maintenance. A-10s ability to fly from forward bases, dirt strips and open fields makes it significantly less vulnerable to such attacks than other aircraft in the NATO inventory.

Further reading

Hrvatski Vojnik, Broj 64., Godina IV, 20. Svibnja 1994. (Croatian Soldier, No.64, Year IV., 20. May 1994.)

http://www.popularmechanics.com/military/a18236/why-the-a-10-warthog-is-such-a-badass-plane/

http://seari.mit.edu/documents/preprints/RICHARDS_INCOSE08.pdf

http://www.pbs.org/newshour/updates/10-aircraft-designer-explains-warthogs-unique-characteristics/

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29 Responses to “A-10 Thunderbolt survivability design”

  1. duker said

    Great story about a still great plane.

  2. syntaxerror9 said

    Best plane ever built for close air support and anti tank mission!
    (If i remember well, a Ju 87’s pilot (maybe Hans-Ulrich Rudel…) was interviewed at the beginning of the programm for the definition of the A-10’s spécifications.)

    Pierre Sprey, once again, is clear as pure water, in his explanations! He is someone to listen carrefully, as John Boyd was.

    No way the F-35 can replace the A10.
    In my opinion, A-10 should stay in the US Air Force inventory as long as possible.

    Good choice, Picard, to point out the survivability aspect as a main factor about the A-10, and Close air Support in general.
    Others factors are keeping target insight, endurance and quick and precise weapons, off course, but they come after survivability; to kill, you must live first! 😉

  3. altandmain said

    Basically the USAF is trying to kill off the aircraft because ideologically, they don’t like it. The ALX v2 should have all the same benefits, although somewhat better owing to small size and superior thrust to weight ratio at 50% fuel (combat).

    I am interested in Pierre Sprey’s design that you wrote about:
    Pierre Sprey’s CAS fighter (America’s Defense Meltdown, pg 161). Sprey’s fighter has 30 mm cannon, 8.000 kgf of thrust, 6.350 kg empty weight, 4.500 kg of fuel (fuel fraction of 0,41)

    It looks like he designed the aircraft with a much more powerful engine.

    I don’t know if there are any further details on the Internet about it. No idea about an airframe design, guns, etc.

    As you note, is also the Blitzfighter:
    http://blacktailfa.deviantart.com/art/Vought-VB-100-Blitzfighter-296126107

    Like your design, it is designed around the 4 barreled 30mm Gattling cannon. It is much smaller too. Much lower fuel fraction, but also very lightweight in total mass. It has a low fuel fraction, and is more of a “point defense” type of CAS than anything meant for loitering.

    If that works out, Sprey’s design might be insanely good for survival. I think he wanted a single engine and his design would look a lot closer to your ALX proposal, second version.

    • picard578 said

      Pierre Sprey described his design as, basically, smaller A-10. As for Blitzfighter, I’m familiar with it. I even had a few discussions with Blacktail.

    • altandmain said

      Hmm … wonder what engines he used.

      Anyways, here is Sprey on a Blitzfighter:
      http://www.allworldwars.com/Proceedings-of-Seminar-on-Air-Antitank-Warfare.html

      Search for:
      COUNTERING A WARSAW PACT BLITZ

      The first part of this is a written transcript of Boyd’s Patterns of Conflict. There is also a question section with Rudel.

      • syntaxerror9 said

        Thanks for the link.

      • Andrei said

        “Hmm … wonder what engines he used.”

        2xGeneral Electric J85-17B, says so towards the end of the post in the link. Same as the Saab 105 trainer. It would have basically been a trainer modified to carry out and survive CAS missions.

      • altandmain said

        Thanks.

        The other is interesting. A rear facing seat for the back pilot as in the Stuka:

        If you used the speed of the A-10 at 900 kilometers an hours, he says, it would be totally useless. You might as well forget about it. You would never see tanks at 900 kilometers an hour. You have to use the low-speed capability of the airplane. That brings up an interesting point that came out at lunch that I think is of major significance here. Colonel Rudel thinks that we have made a terrible mistake in the A-10, and that we would be likely to repeat that mistake in any new airplane, by not having a second seat facing to the rear. He says there is no question in his mind that if you are going to do anti-tank work you cannot do without that second seat. He gives the following reasons. You must give undivided attention to scanning the terrain in order to find the tanks because they are terribly difficult to find. To do that you cannot be distracted by any requirement to look to the rear or to cover your own six. As soon as you have to interrupt your scanning to look back, you are out of the tank finding business, You will not find them It will be impossible. Secondly, there is also the issue that if these airplanes have a high-speed capability and the pilot is in some fear that he is going to be bounced he is simply not going to use the low-speed capability and he will be using the upper end of the speed spectrum, the 900 kilometers an hour that he is talking about on the A-10 or on any new airplane. So you mist have the second seater to cover six simply to give the pilot security so he will be willing to use the low speed, because if he does not use the low speed he is not going to find the tanks and that is all there is to it. He is absolutely definite on that, just unshakably firm in that opinion. I think it is something we have to take very seriously. He is talking about this more. He talks about it much more in terms of just seeing than in terms of defense. As you know, the Stuka had a gunner back there and he has not really brought up the question of the effect of having the gun itself. It is just the effect of having a pair of eyeballs looking to the rear.

        I think as well I read another interview from Rudel claiming that the rear gun on the Stuka was also invaluable.

  4. altandmain said

    The reason why I asked is because Pierre Sprey did propose a single engine design too.

    Here it is:
    http://pogoarchives.org/labyrinth/09/04.pdf

    Scroll to page 15 in that PDF for the single engined sample Blitz design. That probably became the Blitzfighter, but it’s an interesting design. Page 16 has proposed specs.

    I assume the close to 1:1 T/W ratio at 50% fuel that Sprey was considering (closer to 0.9:1) is due to a more efficient engine today?
    Pierre Sprey’s CAS fighter (America’s Defense Meltdown, pg 161). Sprey’s fighter has 30 mm cannon, 8.000 kgf of thrust, 6.350 kg empty weight, 4.500 kg of fuel (fuel fraction of 0,41)

    Wondering if the single engined designs would work better? Perhaps in that regard Picard’s Proposal 2 might be better? Open for debate.

    • Andrei said

      From what I read in Pierre Sprey’s proposal, his Blitz fighter is a little more specialized variant of CAS,specifically meant to search, find, attack and destroy tanks. As such it lacks some features of a slugger like A-10, meant to be more of a generalist CAS aircraft capable both of Search and Destroy of Tanks, but also of staying over the infantry for moral support. The Blitz fighter lacks Armour and is optimized for speed and rapid transition from a fast cruise to a slow “search” cruise (I quote from p.10 “Need “Buttonhook” turn (decel) to convert from fast cruise to close-in attack”). It is also more maneuverable then A-10: it relays on surprise not Armour for protection. From what I read the Blitz fighter was meant to to come in low and fast, do several very fast passed over the tank formation, take advantage of the shock to destroy as many vehicles as possible ( I quote from p. 10 “Rate of kill is critical – attacked units disperse rapidly”/”Above all, need minimum re-attack time (<<35 secs)" ) and then disappear once the tanks had found cover and deployed their AA (on p14 it gives Invisibility as the most critical factor in self defense ) . So while the A-10 can carry out the mission of the Blitz fighter , but slower, the Blitz can not do one of the most important missions of the A-10, simply staying over the battlefield and letting everybody know that BigBro has their back. To take the metaphor further Blitz fighter would be BigBros foul mouthed, small stature, very agile friend that is always behind BigBro and hitting the the Bullies from behind while they are distracted by BigBro staring them down.
      In conclusion, both aircraft would be needed. A dual-engine tank loitering over the main battlefield, or deployed once battle has been joined, and a single-engine speedster darting around the battlefield from hot spot to hot spot or attacking targets of opportunity if the battle has not started and the enemy is still positioning.
      It would be interesting our days to design the Blitz-fighter as a drone, and the tank fighter as a two pilot craft. By getting rid of the pilot the Blitz fighter could be smaller, or carry a bigger gun or more ammo and fuel or a combination of all four. One tank fighter would control several drone Blitz fighters that it could dispatch to distant hot spot, or have them attack the target attacked/marked by the tank fighter. If the drone Blitz fighter is to far away from the tank fighter for the pilots to visually identify the target, the observer could probably use a VR display to see a wide angle point-of-view of the Blitz fighter and identify targets. Or alternatively the Blitz-fighter could attack targets marked by ground troops.

      • altandmain said

        Drone might not work because it needs to be able to make high G maneuvers. Right now drones can’t do that. That and good 360 degree visibility. Drones give a limited field of view.

        Compounding the problem, a competent enemy might find a way to jam the control link or hack the drone (this has already been done before).

        As far as marked by ground troops, to an extent if you think about it, artillery already does that. I’m thinking that until the technology advances, drones are more for recon than anything else. Maybe a small drone with a sniper rifle like weapon. But otherwise, it’s not possible because the enemy will jam the signal and due to high G maneuvers.

      • altandmain said

        Drone might not work because it needs to be able to make high G maneuvers. Right now drones can’t do that. That and good 360 degree visibility. Drones give a limited field of view.

        Compounding the problem, a competent enemy might find a way to jam the control link or hack the drone (this has already been done before).

        As far as marked by ground troops, to an extent if you think about it, artillery already does that. I’m thinking that until the technology advances, drones are more for recon than anything else. Maybe a small drone with a sniper rifle like weapon. But otherwise, it’s not possible because the enemy will jam the signal and due to high G maneuvers.

  5. altandmain said

    Found the other interview with Rudel: http://pogoarchives.org/straus/antitank-warfare-seminar-10-14-1976.pdf

    Page 73 and 74

    He would like very much to see a second seat in the A-10
    for many reasons. One that he will repeat many times is the
    fact that the pilot, when he is attacking, when he is looking
    for a tank, must spend 100% of his time looking for that tank.
    If he must spend time looking in the rear to defend himself, or
    to separate himself from the other aircraft, but most impor
    tantly to defend himself from attacking aircraft, he does not
    nave the concentration on the attack area and on the target.
    He will not be able to find the tanks, which is the most im
    portant thing to begin with. Having a second individual in the
    •aircraft itself has many secondary benefits, one of which is the
    fact that the gunner, as he is describing it, can also help
    spot. It is a second pair of eyes that can say, “I can see him
    now,” “turn at this point” or “there is somebody behind us you
    have got to get out of the area” “you have to change what you
    are doing now.” The other thing is, and especially in his in
    stance is that the second individual was a control, offering
    immediate refutation, if you will, or confirmation of the kill.
    Confiirmation of the fact that you have stopped a particular
    tank. Secondary reason as to why it would be nice to have a
    second individual is the comradeship that there would be
    moral support. If you are concentrating so on what you are
    doing, it assists the pilpt so much to have somebody else in
    there to share his experience with him.

    Another thing extremely important, he believes, is to have a
    second individual to be a gunner with a weapon that he can
    use against attacking aircraft. For several reasons that weapon
    must be one that is a very fast shooting weapon that can put
    a lot of ammunition in the air at the seone time. Specifically
    they discovered that attacking fighter pilots when they found
    that the SiukcL had its own self defense and was shooting at
    them from the rear, became very hesitant to attack that air
    craft and of course that gives them the safety and also more
    peace, if you will, or quiteness to look for their target.
    One other thing. Col. Rudel spoke of control. What he
    meant by this is by having a back seater there, it could
    dampen an over enthusiastic pilot’s B.D.A^. He would act as a
    checker or whatever. The teamwork actually strenghtens the
    pilots pressing in.

    Let me know what you guys think.

    • picard578 said

      Yes, I think that would be good. There is a reason why FAC aircraft have two seats. It lets the pilot concentrate on flying, and you can have a dedicated, trained observer in the back. It significantly improves effectiveness.

      • altandmain said

        I’ve been wondering if it is worth it as well.

        For the rear facing gun, tracers might be desirable because an enemy air superiority fighter chasing the CAS aircraft might be deterred that way (ex: you WANT them to see that you have a means to shoot themselves).

        Interestingly, like the WW2 bombers, the B52 used to have tail guns too. B52H with 20mm Vulcan below:

        Actually, that reminds me, can you approve of 2 comments in moderation for Riley (the Combat Reform cannon fighter link and this) in his proposal?

        • Yeah Even Il-76 uses that actually. That might be an interesting feature for a CAS aircraft, but the minuses are that it would require a bigger thus heavier and costlier (per unit) aircraft.
          As a plus, it might be used remotedly by the back seater who’s presence importance is undiscutable in my opinion. (I would also add that if it is powerful enough it will add thrust foàr the airplane 😀 not unlike the GSh 6-30 wich has a thrust-to-weight ratio around 40:1 or so).
          More seriously, going back to the arguments saying that the principal weakness of an A-10 to IADS (or fighters) is its speed I’d answer this:

          -As an End-Game target:
          an A-10 flying ant 0.45Mach (500 kt) making a 4G turn, will force a Mach 2 SAM to pull 79G’s [speed factor squared by Aircraft’s load factor].
          No SAM can do that…
          Against high speed big SAM’s it gets worst
          And that is actually based on the supposition that this missile is able to track it! as IR MANPADS are pretty much useless in this thanks to the IR concealement measures on the A-10 (maybe if equipped with more modern seekers such as those present on IR AAM’s that would change, but It will prove complex and costly)
          as for EM based it gets trickier (as the A-10 has a big radar cross section) but nothing impossible to overcome; Jamming is largely sifficient for that.

          Against fighters, I will assume that the attackers will remain high (to avoid AAA) thus using only missiles. A 2.5 Mach IR AAM has to pull 123 G’s for a 4G turn at 500 kt by the A-10. Still undoable for current AAm’s…

          What I’m pointing at here is that beeing slow is not that much of a vulnerability, as this increases speed factor relative to missile’s speed.

          Being slow creates though a “vulnerability” to AAA that it overcomes by being toughly armored and extremely maneuverable.

        • Maybe a really dangerous AAA system for an A-10 would be [So Ironically] the Goalkeeper wich uses the same Cannon. Or it’s chinese copy the LD-2000.

          But these are radar cued though, but an optical version wouldn’t prouve very complex to make.

        • altandmain said

          Not sure if the Internet ate my comment, but the slow spin up time is a serious problem from American electric Gatling type weapons..

          A 20mm Vulcan cannon only puts out 20 rounds in the critical first 0.5s.

          202 lb 6-barrel 20mm M61A2 takes ~1/4 second to spool up to 6000 rnd/min
          248 lb 6-barrel 20mm M61A1 takes ~1/3 second to spool up to 6000 rnd/min
          270 lb 5-barrel 25mm GAU-12 takes ~0.4 second to spool up to 4200 rnd/min
          620 lb 7-barrel 30mm GAU-8 takes ~0.7 second to spool up to 4200 rnd/min

          Note the GAU-8’s 0.7s spin up time. That won’t do well in an anti air roll.

          Russian gas operated weapons are far better in that regard. AK 630 variant with 2x Gsh-6-30 gas operated Gatling gun is an example on Russian Navy ships. Here is the AK-630M-2:

        • picard578 said

          I think revolver cannons offer ideal compromise between spin-up time and maximum rate of fire. Linear-action guns don’t have spin-up time but have low RoF, and rotary guns have high rate of fire but long spin-up time.

        • altandmain said

          That’s why I like gas operated Gatling cannons like the Russian designs. Near instant spin up and very rapid rate of fire. They are also lighter in mass IIRC than the electric guns because they don’t need external power.

          Revolvers I guess do have very rapid spin up, but rate of fire isn’t as good.

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