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Aviation History
1940
1940 - 1284.PDF
408 MAY 2, T940 actual installation depending on the design of the wing. Sometimes the gun is mounted upright and in other cases is placed on its side. If it is desired to keep the gun within the wing contour the latter method is better. Pneumatic or electric control is available though the cocking is always done pneumatically. For mounting on an engine the requirements are a hollow airscrew hub through which the barrel may pass and small local modifications. In view of the fact that the mounting is constituted by the engine itself, repre- senting a heavy mass, the engine gun has been evolved from the " FFS" weapon, with an initial velocity of 830 m/sec, and bears the designation "FFS/MK." There is a double-acting axial spring arrangement fitted to the barrel in connection with a rear sliding bearing. Generally a 60-round drum magazine is provided for the engine gun which can have pneumatic or electric control. As there are many popular misconceptions about the relative merits of wing and engine-mounted armament, it may be pointed out that the engine gun, with its higher initial velocity, has a certain advantage in its flatter trajectory, though, on the other hand, a pair of wing Two views of the20 mm. Oerlikon designed for employ-ment against aircraft and tanks. A fifteen-round magazine is used, guns provide more than double the rate of fire while weighing approximately the same as one engine gun. For rigid mounting in the fuselage, either the mediuir "FFL" or the heavy "FFS" guns may be used. In certain installations the guns are accessible, so that the magazines can be changed. Initial velocity does not play such an essential part in present-day air fighting as is frequently ascribed to it, and it is considered that the velocity of the "FF" wing gun fully meets current requirements. -., Free Quns For movable mountings with a forward field of fire the light " FF " or the medium "FFL " gun should be selected to avoid the use of heavy or cumbersome mount- ings. On comparatively slow machines a simple swivel can be used for mounting a gun of the " FF " type, an appropriate shoulder rest being provided. The heavier type '' FFL '' can be used with a special trunnion mount- ing controlled through gears, the trigger being actuated from the hand wheel. In both cases the gunner has direct control, and the gun is provided with levers for single fire and automatic fire, and with a device main- taining the breech cocked after the last round has been fired. In the first place the breech is cocked by means of the pneumatic cocking device. The compressed air is supplied by a small flask holding three litres and fitted to the mounting within easy reach. In order to facilitate changing of magazines, drums of small capa- city—20 to 30 rounds—are • -• ': used as a general rule. • ; The only one of the guns considered suitable for a manu- ally trained stern installation is the type "FF." To facilitate changing magazines, drums of 20 rounds capacity are nor- mally used. Naturally, powered mountings would be very desirable, but no informa- tion on these is yet available. For infantry use the neces- sity of engaging aerial or ground targets must be con- sidered. One of the reasons (Below) The heavier type FFL can be used on a trunnion mounting con- trolled through gears. (Below) Cockpit mount-ing with the 20 mm. Oerlikon type FF gun. put forward in favour of having two different weapons is that tanks can be fought most effectively by using a comparatively large shell. Since the weight of utomatic weapons of adequate bore (37-47 mm.) prohibits their use by infantry, the automatic function « waived in favour of the greater effectiveness of the single shot. ,, . The 20 mm. Oerlikon type JLab na_
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