Weapons For Air F I

arrangements because of the distance from the engine.

The traditional inter-war twin-RCMG equipment was almost invariably mounted in the engine cowling and synchronised to fire through the propeller disc. As the number and size of guns increased, differences in national preferences began to emerge. Soviet, German and Japanese practice generally continued to favour cowling-mounted synchronised guns and Soviet, German and French air forces also used aircraft with engine-mounted cannon. In contrast, British and (slightly later) American practice favoured fitting a relatively large number of guns, which made wing-mounting unavoidable.

A particular problem was caused by the tendency in most air forces to fit mixed armament, i.e. RCMGs, HMGs and cannon, especially where the ballistics of the weapons varied. The differing trajectories of the projectiles meant that they could only be adjusted to strike a single aiming mark at a particular range; at shorter distances the lower-velocity guns would strike above the higher-velocity ones, at longer distances the reverse would apply. Different times of flight could also cause significant problems in deflection shooting. Finally, the aiming problems with mixed armament were exacerbated (except at short range) whenever aircraft fired while banking; the lower-velocity projectiles fell off more to one side (from the pilots point of view) as gravity had more time to affect them.

The consequences are illustrated by wartime tests of the British Hurricane IID ground-attack aircraft, equipped with two 40mm guns and two RCMGs for sighting. Shooting the 40mm guns with HE ammunition proved to be twice as accurate as with AP; the muzzle velocity of the HE rounds matched that of the RCMG, while the heavier AP shot had a significantly lower velocity.

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