Close Air Support fighter proposal 3

Introduction

As EJ-230 turned out to be too expensive for estimated cost of aircraft, I have decided to replace it with commercial engine. Gun will also be replaced with 30 mm version of GAU-12 (henceforth GAU-32). 20% increase in size will result in gun being 2,53 m long, 0,31 m wide and 0,35 m tall. Projectile dimensions will be 30×173 mm, same as GAU-8. Rate of fire will be 4.200 rpm, with muzzle velocity of 1.000 m/s. Projectile weight will be 378 g, with total round weight of 681 g. Muzzle energy will be 189.000 J, and maximum output 13,23 MW. Gun itself will weight 211 kg. Recoil is (4.200 / 60) * 1.000 * 0,378 = 26,46 kN.

Design

AX

Length: 12,04 m (12,6 m with tail)

Wingspan: 12,97 m

Height: 3,2 m

Wing area: 26,5 m2

Empty weight: 6.500 kg

Fuel capacity: 4.900 kg

  • Rear tank: 160x110x199 cm = 16x11x19 dm = 3344 l
  • Forward tank: 220x110x110 cm = 22x11x11 dm = 2662 l
  • 1 l = 0,82 kg

Fuel fraction: 0,43

Weight: (30 mm GAU-12 round: 681 g, AGM-65: 300 kg)

With 100% fuel + 1.200×30 mm rounds: 12.217 kg

With 50% fuel + 1.200×30 mm rounds: 9.767 kg

With 100% fuel + 1.200×30 mm rounds + 4 AGM-65: 13.417 kg

With 50% fuel + 1.200×30 mm rounds + 4 AGM-65: 10.967 kg

Maximum takeoff: 13.940 kg

Wing loading:

With 100% fuel + 1.200×30 mm rounds: 442 kg/m2

With 50% fuel + 1.200×30 mm rounds: 350 kg/m2

With 100% fuel + 1.200×30 mm rounds + 4 AGM-65: 487 kg/m2

With 50% fuel + 1.200×30 mm rounds + 4 AGM-65: 395 kg/m2

Weapons:

1xGAU-32 with 1.200 rounds

6 wing hardpoints (70 mm rocket pods, 12 rockets each; AGM-65 Maverick, AGM-114 Hellfire, AIM-9, ASRAAM, IRIS-T, MICA IR)

1 centerline hardpoint (jamming pod or 500 kg fuel tank, or any of above)

Gun: GAU-32

Length: 2,53 m

Width: 0,31 m

Rate of fire: 4.200 rpm

Muzzle velocity: 1.000 m/s

Projectile: 378 g

Round: 681 g

1-second burst: 70 rounds / 13,23 MJ

Engines: ALF-502R-5 (statistics represent each engine)

Maximum thrust: 6.970 lbf (3.162 kgf, 31 kN)

SFC at maximum thrust: 0,408 lb / lbf hr

Fuel consumption at maximum thrust: 1.290 kg per hour

Cruise thrust: 2.250 lbf

SFC at cruise thrust: 0,72 lb / lbf hr

Fuel consumption at cruise thrust: 735 kg per hour

Length: 162 cm

Diameter: 102 cm

Wing loading:

488 kg/m2 at combat takeoff weight

395 kg/m2 at combat weight

Thrust-to-weight ratio:

0,47 at combat takeoff weight

0,58 at combat weight

Speed:

Maximum: 860 kph

Cruise: 490 kph

Combat radius with 10 minute combat: 1.093 km

Combat radius with 10 minute combat and 2 hour loiter: 603 km

Sensors:

radar warners

laser warners

missile warners

Countermeasures:

chaff

flares

Unit flyaway cost: 9.184.000 USD

Cost per flying hour: 1.000-1.500 USD

Sorties per day per aircraft: 3

Sorties per day per billion procurement: 324

ax

Notes

  • large tank: 140*98*122 px = 12,38*8,67*10,79 dm = 1158 l
  • small tank: 56*52*122 px = 4,95*4,6*10,79 dm = 245 l
  • wing tanks: 2 * 504*84*8 px = 2 * 44,59*7,43*0,71 dm = 2 * 235 = 470 l

This will allow extensive combat and loiter time even if one fuel tank is punctured.

ALX combat mission fuel usage will be like this:

* takeoff – 7 kg

* 10 minutes to 10.000 meters – 430 kg

* 10 minutes of combat – 430 kg

* descent – 250 kg

* landing – 4 kg

* cruise to combat area – 1.640 kg

* cruise from combat area – 1.640 kg

* unusable fuel – 10 kg

* reserve – 489 kg

Ammo capacity:

l:72 px / 63 cm, d:92 px / 80 cm

area: 450 rounds

length: 3 rounds

total: 1.350 rounds

weight: 702 kg

Wing area: 2*210*582 + 97*215 = 244.400 + 20.855 cm2 = 26,5 m2

A-10 costs 16 million USD at weight of 11.321 kg, for a cost of 1.413 USD/kg.

Naval variant will cost 11 million USD.

EDIT:

A-10 has a minimum takeoff distance of 945 meters and landing distance of 610 meters. Its takeoff weight is 21.361 kg for CAS mission, with TWR of 0,38, wing loading of 454 kg/m2. ALX has a takeoff weight of 13.417 kg, TWR of 0,47 and wing loading of 488 kg/m2.

Decrease in takeoff distance is proportional to increase in TWR. 10% increase in takeoff weight increases the takeoff run by 21%. 10% increase in landing weight increases the landing run by 10%. 10% increase in wing area (9% decrease in wing loading) decreases the takeoff speed by 5%.

Thus the ALX takeoff distance is 427 meters. (945 m > 407 > 427)

Loadouts

ax

Comparision with other fighters

AX’s weapons loadout allows it 24 attack passes; A-10 for comparision has 22 firing passes of gun ammo and 6 missiles, for total of 28 attack passes. A-10s unit flyaway cost of 16 million USD and 3 sorties per day per aircraft however mean that while A-10 can fly 186 sorties per day per billion USD, AX can fly 324 sorties per day per billion USD; a 1,74:1 sortie generation advantage; this means that AX offers 7.776 attack passes per billion procurement USD per day, compared to 5.208 for the A-10. AX is also less visible and somewhat more maneuverable owing to higher thrust-to-weight ratio and smaller size, resulting in greater survivability.

Comparing it with other fighters that are supposed to perform CAS is nowhere near being a fair play: aside from being completely incapable of performing actual CAS, fast jets are also too costly. F-16C costs 70 million USD flyaway and can fly 1,2 sorties per day, resulting in 16 sorties per day per billion USD (a 20:1 advantage for AX); F-35A costs 184 million USD flyaway and can fly 0,3 sorties per day, resulting in 1,5 sorties per day (a 216:1 advantage for AX).

F-16C has 4,7 1-second bursts from gun and can carry up to 12 bombs, for a total of 17 attack passes; F-35A has 2,6 1-second bursts and can carry up to 10 bombs, for a total of 13 attack passes. Thus per billion procurement USD, F-16C offers a total of 272 attack passes, and F-35A offers a total of 20 attack passes. From this it can easily be calculated that, for equal procurement cost, F-16C offers 13 times as many attack passes as the F-35A, A-10 offers 260 times as many attack passes as the F-35A, and AX offers 389 times as many attack passes as the F-35A.

It is also interesting to compare it to several proposed CAS fighters. First one is 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), 11.300 kg combat takeoff weight; likely cost is 9 million USD. Another Fighter Mafia’s proposal, “Blitz Fighter” by James Burton (made into concept at LTV Vought Company), an airplane with empty weight of 2.300-4.500 kg, using 4-barreled 30 mm Gattling gun and a minimum of sensors; it would have cost 7,4 million USD (adjusted for inflation to 2013 USD). AX has 30 mm cannon, 6.324 kgf of thrust, 6.500 kg empty weight, 4.900 kg of fuel (fuel fraction of 0,43), 13.417 kg combat takeoff weight, and while it can carry guided AT missiles, it relies primarly on its gun and dumb weapons; it costs 9,2 million USD. It can be seen that while AX is not as radical concept as other two fighters, it offers most of the same advantages.

3D design by Riley Amos (added 16.8.2016.)

https://3dwarehouse.sketchup.com/model.html?id=6844bedc-c4b9-4d53-9f7c-5babdd827953

alx-riley-amos

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144 thoughts on “Close Air Support fighter proposal 3

  1. Some interesting links:

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

    View story at Medium.com

    View story 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.

    • 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.

  2. 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

    • 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.

  3. @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.

    • 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.

    • 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.

  4. 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.

    • “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.

    • 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.

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

    1. Define role (ex: tank destroying).
    2. Design the gun (unlike A-10, we will want faster spinup time).
    3. Incorporate all lessons of the least.
    4. 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.

    • 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.

      • “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.

      • 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.

  6. 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.

    • 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.

  7. 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

    • 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.

      • 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.

        • “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.

      • 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.

        • “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.

      • 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.

        • “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
          https://bib.irb.hr/datoteka/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.

      • “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.

        • “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).

      • 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?

        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.

        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.

        • “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.

      • 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.

        • “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.

      • 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.

        • “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.

      • @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.

      • “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.

        • “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.

      • 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).

    • @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)

    • 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:

      • 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.

      • “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:

        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.

    • 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.

      • 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.

        • “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.

  8. 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.

  9. @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.

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

    • 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.).

  11. 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.

  12. 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.

    • 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).

      • 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.

        • “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.

      • 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.

    • 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).

    • 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).

      • 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.

        • 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.

  13. 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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