Weapons For Air F I

attempts to produce an effective air-fighting gun, followed by more successful use as airborne anti-tank guns.

In the lead-up to the Second World War, aircraft designers had a wide choice of rifle-calibre (7.5-8mm) and heavy machine guns and large-calibre cannon from which to choose. Trying to decide which combination of weapons would be best was not easy, even with war experience, because the circumstances kept changing. The basic characteristics which had to be taken into account when drawing up armament specifications were:

1.The weight of the gun and of the ammunition (typically for up to twenty seconds' firing although some early drum-fed cannon were limited to much less by the magazine capacity). This determined the number of weapons which could be carried within a given weight limit.

2. The rate of fire of the gun, or more significantly of the total number of guns carried. This was increasingly important given the improving performance of aircraft, which limited the time available for firing.

3. The muzzle velocity of the projectiles, which determines the time of flight to the target; the shorter this is, the greater the hit probability, especially where rapidly manoeuvring targets requiring deflection shooting are concerned (US wartime calculations indicated that a 50% increase in muzzle velocity tripled the chance of a hit).

4. The destructive effect of the projectiles, in terms of armour-piercing ability and (for cannon shells) explosive power - particularly important in dealing with bombers.

5. The range of the armament, a function of calibre and muzzle velocity, which became important to both sides in the battles between bombers and fighters.

The rifle-calibre machine guns were light, compact and fast-firing. They normally weighed 10-15kg and fired bullets weighing 9—12g at 730-850 m/s at a rate of about 1,200 rpm (typically reduced to about 1,000 rpm in synchronised installations). There wasn't much variation in performance between the guns of the warring nations, although the Soviet 7.62mm ShKAS achieved 1,800 rpm and

Mg81z Automatic Cannon

2cm Becker-Semag on ring mounting (BuOrd: USN)

IMPin F I 11 F

the Mauser MG 81Z twin no less than 3,200 rpm

The skill and training of pilots also affected this with a weight of only 9.5kg. Their effectiveness issue. By and large, expert fighter pilots who were diminished during the Second World War as air- confident of their shooting preferred few guns, craft adopted armour plating and self-sealing fuel whereas a larger number of guns gave novices more tanks. There was some use of incendiary (and even chance of scoring hits.

HE) projectiles of which the RAF s 'De Wilde' incendiary was particularly well known.

Bomber aircraft logically needed defensive armament capable of defeating fighters, and therefore

HMGs were typically about two or three times as should have possessed weapons at least equal in heavy as RCMGs and fired more slowly at about range and hitting power. In fact, a British inter-war

750-900 rpm. Muzzle velocities were similar to the study concluded that bombers needed more power-

lighter weapons but the bullets were appreciably ful weapons in order to destroy the engines of fight-

heavier at 35-55g; they were accordingly much ers as they attacked head-on. In practice, the size of more effective against armoured targets, could weapons fitted was more limited than in fighter air-

carry more incendiary material and had a longer craft. Bomber armament was either free-swinging, range. in which case a heavy machine gun or low-powered

As might be expected, cannon were heavier and 20mm cannon was usually as much as could be slower-firing still, although the range of specifications was much wider. The Becker's line of development continued via SEMAG and then Oerlikon, handled, or turreted, which again placed limits on size and weight.

An issue in single-engined fighters was the loca-the Erhardt's via Solothurn and then directly by tion of the armament. The ideal armament layout Rheinmetall. By the late 1930s there were several was to have the guns mounted near the centre-line different 20mm guns available offering a wide range of the aircraft; this concentrated the fire, kept the of performance, from the Oerlikon FF at the low weights close to the centre to assist manoeuvrabili-end of the muzzle energy spectrum to the Swiss HS ty and provided the most solid and substantial

404 and FMK, Danish Madsen and Japanese Ho-1

mounting in the interests of accuracy and of and Ho-3 at the other. Few larger guns existed at absorbing the recoil of heavy weapons. This was that time, although there was some interest in easily achieved with twin-engined aircraft, but the

23mm guns and also in new weapons in 37mm calibre.

problem with single-engined fighters was that the ideal aircraft layout for optimum performance and

As with all weapon systems, it was necessary to handling - front-engined, with a tractor propeller reach a compromise between conflicting requirements. The balance of the characteristics chosen for fighter aircraft depended on the nature of the likely was the worst for mounting guns because the engine and propeller got in the way.

There were therefore three alternatives: to mount opponents. Bombers were relatively large, easy tar- a gun to fire through the hollow propeller hub (only gets but their size made them difficult to shoot possible with vee-engined aircraft designed to down and they usually carried defensive machine accept this, and only room for one gun anyway); to guns. The most important characteristics were mount the guns in the engine cowling or wing roots therefore destructive effect and range.

and synchronise them to fire only when the pro-

Fighters on the other hand were easier to dam- peller blades weren't in the way (which added age but much more difficult to hit. The rate of fire complication and reduced the guns' rate of fire -

and muzzle velocity were most important, although typically by 10-20%); or to mount them in the during the course of the Second World War wings and accept the disadvantages. These included destructive effect became more significant as fight- dispersed weights (affecting manoeuvrability), ers acquired armour plate and protected fuel tanks. dispersed fire (the guns had to be adjusted to con-

The heavier the armament carried, the more the centrate their fire at particular distances), reduced performance and handling of the aircraft were accuracy due to wing flexing during gun firing and degraded, particularly important when facing manoeuvring, problems in absorbing the recoil opposing fighters.

of powerful cannon, and special gun-heating

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