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Close Air Support fighter proposal 3

Posted by Picard578 on December 28, 2013

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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175 Responses to “Close Air Support fighter proposal 3”

  1. tdcoish said

    Picard,

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

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

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

    • 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:
      https://defenseissues.net/2014/08/16/forward-air-controller-aircraft-proposal-revised/
      Endurance of 9 hours, combat radius 1.850 km, fuel fraction 0,17, albeit estimates may not be entirely accurate.

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

  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
    -Lighter
    -Smaller width, height
    -(Negative) larger length

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

  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.

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