Despite repeated proclamations about the “end of the dogfight”, gun has always remained an important part of fighter aircraft’s armament. There are several reasons. Having a gun provides a psychological security of having a fallback option if missiles are expended. Gun also has far lower minimum range than even most agile of modern dogfighting missiles (very short ranges reduce missile kill probability even if target is not within missile’s minimum range), and is the most versatile weapon aircraft has – it can be used in dogfight (shooting down aircraft), in air policing (warning shots) and ground attack. While some fighter aircraft sent into Vietnam war didn’t have onboard cannons, low kill probabilities of missiles – especially long-range radar-guided missiles – resulted in guns being reintroduced. Another issue is that, even today, visual identification of target is the only reliable way of identifying it – and many fighter aircraft still do not have imaging IRST or other optical sensor capable of identifying targets at beyond normal identification range of several hundred meters.
Measures to be used in comparision
Due to the nature of air combat, firing opportunities are very brief – only rarely will the enemy present most favorable aspect, and will even more rarely keep up a steady-state maneuver. This means that high-deflection shots, and especially snapshots, are very common, and length of burst is almost never greater than 1,5 seconds, and is often shorter (typically 0,5-1 second).
Thus, a fighter gun has to have:
- heavy firepower
- large number of bursts
- good effective range
Firepower depends on following factors:
- number of projectiles fired
- projectile mass
- HE-I content
Number of bursts depends on:
- number of shots fired per burst
- number of shots carried
Effective range depends on:
- muzzle velocity
- projectile crossectional density
- drag coefficient
Guns compared will be those of fighter aircraft in comparision of modern fighter aircraft done earlier: Eurofighter Typhoon, Saab Gripen (BK-27), Dassault Rafale (GIAT 30), F-22 (M61A2), F-35 (GAU-22/A), HAL Tejas (GSh-23), JF-17 (GSh-23-2), J-10 (GSh-23-2?), J-11 (GSh-30-1), Su-30 (GSh-30-1), Su-35 (GSh-30-1).
|Gun||Projectile mass||HE-I content (%)||Rate of fire (rpm)||Spin-up time (s)|
|GIAT 30||275 g||17,5||2500||0,05|
|GAU-22/A||184 g||16,7 (?)||3300||0,4|
Thus we have:
|Gun||Projectiles in 0,5 s||Mass in 0,5 s||HE-I in 0,5 s||Muzzle velocity||Projectile crossectional density|
|BK-27||13||3,38 kg||0,507 kg||1100 m/s||45,41 g/cm2|
|GIAT-30||19||5,23 kg||0,914 kg||1025 m/s||38,9 g/cm2|
|M61A2||37||3,77 kg||0,389 kg||1050 m/s||32,47 g/cm2|
|GAU-22/A||16||2,94 kg||0,492 kg||1040 m/s||37,48 g/cm2|
|GSh-23-2||30||5,25 kg||0,567 kg||715 m/s||42,12 g/cm2|
|GSh-30-1||12||4,8 kg||0,595 kg||860 m/s||56,59 g/cm2|
Number of burst per aircraft is as follows: Gripen C (BK-27): 9,2, Typhoon (BK-27): 11,5, Rafale (GIAT-30): 6,6, F-22 (M61A2): 13, F-35 (GAU-22/A): 11,3, HAL Tejas (GSh-23): 7,3, JF-17 (GSh-23-2): unknown, J-10 (GSh-23-2?): unknown, J-11 (GSh-30-1): 12,5, Su-30 (GSh-30-1): 12,5, Su-35 (GSh-30-1): 12,5.
As it can be seen from table, GIAT 30 is by far the best cannon when it comes to firepower, and combination of good muzzle velocity and projectile crossectional density results in good effective range. BK-27 has very good effective range thanks to high muzzle velocity and excellent projectile crossectional density, but limited (albeit still good) firepower. Russian guns also have good firepower and excellent projectile crossectional density but are let down by low muzzle velocity, suggesting an orientation towards the ground attack. US M61A2 has good muzzle velocity, but low crossectional density limits effective range, while low HE-I content and rotary design limit effective firepower. GAU-22/A has better HE-I content but less throw weight; still, good muzzle velocity and projectile crossectional density result in good effective range, though it may be limited by dispersion due to rotary design.
Since most important factors in gaining kills are mass of the projectile, HE-I portion, muzzle velocity and rate of fire, GIAT 30 is overall the most effective cannon when it comes to ACM (dogfight) employment. However, Rafale has a relatively limited number of gun bursts avaliable (adequate for a single kill). On face of it, best balance between number of gun bursts and their effectiveness seems to be achieved by Gripen and Typhoon. This may not be as great shortcoming on Rafale’s part, however, since GIAT 30 offers an option to reduce rate of fire to 1.500 rpm; this leads to 11 projectiles fired in first 0,5 s, weighting 3,03 kg with 0,529 kg of HE-I, allowing for a total of 11,4 bursts while achieving similar effectiveness to the BK-27 (and better than any other gun compared). Overall, European approach seems to be the most effective, with US sacrificing firepower, accuracy and response time in exchange for lower barrel wear and greater ammunition capacity, while Russians sacrificed muzzle velocity and HE-I content for greater round weight. This suggests that while European focus is on dogfight performance, US focus is on shooting down bombers while Russian focus is on ground attack performance.