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  • December 2013
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Close Air Support fighter proposal 3

Posted by Picard578 on December 28, 2013


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.



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


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


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


radar warners

laser warners

missile warners




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



  • 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.


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)



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.)


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197 Responses to “Close Air Support fighter proposal 3”

  1. tdcoish said


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

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

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

    • tdcoish said

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

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

      • Picard578 said

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

    • Picard578 said

      Yes, turboprop is far more efficient. That is why I used it for my FAC/COIN/light CAS aircraft:
      Endurance of 9 hours, combat radius 1.850 km, fuel fraction 0,17, albeit estimates may not be entirely accurate.

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

  2. tdcoish said

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

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

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

    • Alex said

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

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

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

  3. tdcoish said

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

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

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

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

    • Picard578 said

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

      • tdcoish said

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

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

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

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

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

        • tdcoish said

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

        • Riley-Amos said

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

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

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

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

        • tdcoish said

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

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

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

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

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

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

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

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

        • tdcoish said

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

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

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

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

        • tdcoish said

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

        • tdcoish said

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

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

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

        • Riley-Amos said

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

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

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

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

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

        • Riley-Amos said

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

        • altandmain said

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

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

  4. tdcoish said

    Advantages and disadvantages of RCLR vs Rockets:

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

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

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

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

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

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

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

    • tdcoish said

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

      • Riley-Amos said

        Easier to reply if it’s seperate.

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

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

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

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

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

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

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

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

        • tdcoish said

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

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

          No duplicate.

        • tdcoish said

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

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

    • Riley-Amos said

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

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

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

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

      • tdcoish said

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

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

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

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

        • Riley-Amos said

          I’ve drawn up a thought for fin stabilisation, really nothing new:

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

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

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

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

    • Picard578 said

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

  5. altandmain said

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

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

    1. If we are going to be using a taper bore (or squeeze bore), then we will need the projectile itself to be tungsten. The WW2 era guns had powder that weighed almost as much as the projectile. There were also issues with accuracy fall off that will have to be addressed with range.

    2. I will have to find the thread on recoil less rifles, but we did find some engineering challenges. We never concluded if they were insurmountable or not.

    3. I am not sold on the GAU family of gattling guns. They take 0.5 to 1 second to spin up to maximum fire. Revolver will be needed or a gas operated gattling gun, which is what the Russians use.

    That leaves us with a weapon with the following:

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

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

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