Edited to add:
I cannot cite references or sources stating the reason why a caliber larger than the 102x20mm was chosen. However, one of the first 3 PDF's I attached to the original post of this thread stated that the gun system was primarily intended for air-to-ground use. Either in that same document, or something I read in the past day or so, stated that the gun was estimated to be used about 70-80% of the time in an A2G role, and only 20-30% in an air-to-air role.
mixelflick wrote:First all new gun since the Vulcan used in everything from the Phantom to Raptor, correct?
The AV-8B is (optionally) equipped with a 5-barrel GAU-12/A
Avenger gun system, from which General Dynamics derived the GAU-22/A used on the F-35. Various AC-130 gunships have also used the GAU-12/A.
mixelflick wrote:The bigger round is a step up and should do the job strafing most targets. It'll never be the GAU-8 but hey, what is? Hopefully it can punch a hole in a tank, or at least keep their heads down for a bit.
The GAU-8/A on the A-10 kills tanks by defeating the tank's armor where it is thinner (think top, sides, and rear). I do not have memorized the armor penetration values for the 30x173mm round the A-10 carries. The Nammo APEX PGU-47/A round will penetrate 50mm rolled homogenous armor (RHA) at 0° incidence. Taking into account a realistic incidence angle (30-45° ?) suggests there are places on modern MBTs that may be vulnerable to an F-35 strafing it: typically the top / back part of the turret, and/or the top / back part of the rear deck where the engine is typically located. That being said, I don't think anyone considers the GAU-22/A to be a primary tank-killing weapon of the F-35. That would be a SDB-II, SPEAR, or possibly a GBU-49.
The US appears to be standardizing on either a FAP or PELE round by ATK. IMO, the APEX is superior as it is usable across the full spectrum of targets from soft to hard, whereas FAP/PELE seems more appropriate to harder targets as they do not utilize any explosives.
mixelflick wrote:Of more interest to me is its air to air "punch". For decades we seem to have favored the lighter M61 20mm cannon for use in our fighters. The Russians and Europeans, heavier 23 and 30mm rounds (though carrying fewer of them than the M61). So what's the thinking here? Need more "umph" to cause more damage to bigger and more powerful (Flanker) airframes? Or is the move to 25mm solely to find a sweet spot for air to ground/air to air engagements?
If you perused any of the PDF's I included in the first post of this thread, you will see that the gun system is (was) not intended to be a primary air-to-air weapon. It's intended, primary use is to service ground targets.
With that said, air-to-air gunnery is a tradeoff between accuracy, dispersion, shell velocity, shell lethality and firing rate. You want the gun to be
accurate, yet you want a
"dispersion" pattern at your optimum firing range to maximize the chances that a shell will detonate on the target (think shotgun pattern size at expected target distance). A former Phantom driver told me you ideally wanted 50 kts overtake or closure speed, and optimum firing distance was 1000-1500ft. He said you did not want to engage closer than 500ft (if saddled up) because the risk was high that you would fly through a debris field, to the detriment of your own jet's health. Also, 2000-2500 ft would be a really long shot.
High velocity minimizes time of flight (TOF) of the projectiles, removing as much guesswork as possible from estimating where the target will be after 1 TOF (since both attacking aircraft and target are moving in 3D at (typically) high rates, afterall.)
Firing rate relates to shot density (think number of pellets in a shotgun blast.) In fact, the shotgun analogy is apropos here. Do you choose a 12 gauge 00 shell with 9 pellets or a #7 shot shell for birds with lots and lots of tiny pellets? Percentage chance that you hit the target increases with the number of pellets, but the damage inflicted decreases with the smaller pellet size. What works for a duck probably won't work on a bear. For air-to-air gunnery, the US has historically favored higher firing rate and accepted smaller projectile size & mass with the 102x20mm round and the M61 Vulcan as the air-to-air cannon of choice since its choice on the F-104. Since WWII, the Europeans and Russians have favored 27mm or 30mm for their fighter aircraft cannon.
If you multiply firing rate by shell mass, you obtain
throw weight which is a common metric used to compare aircraft gun systems. A succinct summary comparing the various aircraft cannons can be found in this post on ar15.com:
F-35A, 25mm GAU-22/A with 180 rounds.
3300 RPM / 55 RPS rate of fire, 223 gram projectile weight for 12.3 kg/s throw weight, 3.27 seconds firing time of ammunition and 40.1 kg of total projectile weight.
F/A-18E/F, 20mm M61A1 with 412 rounds.
6000 RPM / 100 RPS rate of fire, 102 gram projectile weight for 10.2 kg/s throw weight, 4.12 seconds firing time of ammunition and 42.0 kg total projectile weight.
Typhoon, 27mm BK 27 with 150 rounds.
1800 RPM / 30 RPS rate of fire, 260 gram projectile weight for 7.8 kg/s throw weight, 5.00 seconds firing time of ammunition and 39.0 kg total projectile weight.
Gripen, 27mm BK 27 with 120 rounds.
1800 RPM / 30 RPS rate of fire, 260 gram projectile weight for 7.8 kg/s throw weight, 4.00 seconds firing time of ammunition and 31.2 kg total projectile weight.
Rafale, 30mm GIAT 30 with 125 rounds.
2500 RPM / 42 RPS rate of fire, 275 gram projectile weight for 11.6 kg/s throw weight, 2.98 seconds firing time of ammunition and 34.4 kg total projectile weight.
Su-35, 30mm GSh-30-1 with 150 rounds.
1800 RPM / 30 RPS rate of fire, 390 gram projectile weight for 11.7 kg/s throw weight, 5.00 seconds firing time of ammunition and 58.5 kg total projectile weight.
The biggest difference with the F-35A and GAU-22/A is that it has more programmable bursts. For A2A, you could get 9 x 20rd bursts if you wanted, or 3 x 60rd bursts, etc.
One of the assumptions most outside observers have made is that the F-35 will rely on missiles for its first kills in A2A, when the gun is more of an option in the F-35 than any 4th Gen jet as a first kill system when approaching VLO. Threat air is flying along, all of a sudden they get shredded by 25mm dual-purpose projectiles and don't know why.
https://www.ar15.com/forums/general/F-3 ... #i74212670
IMO, the GAU-22/A represents a masterful compromise, especially if the Nammo PGU-47/U APEX round is used, of
- high rate of fire (though not as high as the Vulcan, but probably more than "dense enough for air-to-air work)
- very good throw weight (in fact, highest of all cannon listed above)
- decent total throw weight
- high velocity (~1000m/sec)
- very good shell lethality against both soft and hard targets (PGU-47/U APEX)
- very good gun accuracy / low dispersion (nascent F-35 aiming issues aside)
- high round / burst efficiency with the ability to select very short bursts (e.g. 12-15 rounds each)
That is, the GAU-22/A appears to be a really good gun system, quite possibly the best in any modern fighter, 4th or 5th generation. It will certainly shred trucks and kill APC's and light armor. It appears it may be effective against armor if attacked from the correct direction.
If combined with a combat autopilot function (think AutoGCAS for a gun solution), it may be a truly killer air-to-air solution especially combined with efficient, short round count bursts.
I hope I have addressed your questions.
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
17 Nov 2018, 05:35
