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Aviation History
1955
1955 - 0105.PDF
105 AIRCRAFT ARMAMENT PART I THIS is a particularly appropriate time at which to reviewthe subject of aircraft guns. The British and Americanair forces are now introducing examples of what may be the last basic family of airborne cannon—for it seems probable that, during the next decade, guns as we know them today will be progressively superseded by other types of weapon; in fact, as is shown elsewhere in this issue, the process has already begun. Before discussing specific types of gun we may briefly considersome of the criteria governing acceptance or rejection of this type of armament. One of the principal factors is weight. The modernaircraft cannon has an installed weight, with accessories, of between 150 and 450 lb, and a single round of ammunition, plus belt link,weights about 0.9 lb (20 mm) or 2.1 lb (30 mm). Thus, an installa- tion of four 30 mm guns, each with 300 rounds of ammunition,would weigh no less than 4,000 lb. Allowance also has to be made for the weight penalty of the mountings and surrounding airframestressed to carry the armament and recoil loads. The principal alternative type of armament is the self-propelledweapon, either of the unguided or guided variety. The unguided missile is not new in concept, but it is only in the past three yearsthat it has actually begun to supplant the gun. Even today, gun- less armament is found only in U.S.A.F. all-weather squadrons.The air-launched guided weapon is of much later conception and is not yet in full service anywhere. All self-propelled missiles enjoy a great advantage over the gun,in that they require no more than a rudimentary launching mechanism. Furthermore, they can be treatedalmost as can a "dead" store, such as a supply container, in that no muzzle flash or recoil has tobe dissipated. Consequently, weight can be saved on these grounds. Any attempt at a relative assessment of gunsversus self-propelled weapons can arrive at only general conclusions. Use of self-propelledmissiles may permit an overall saving in weight, particularly after the weapon has been launched.Accuracy of guided and unguided missiles can be adequate at all ranges at which they can beused, and this range can be considerably greater than that possible with gun armament. Indi-vidual missiles are larger and far more costly than gun ammunition (this is particularly trueof guided weapons, which may cost as much as 100,000 rounds of 20 mm); but this is offset bythe fact that one strike is normally sufficient to knock out any aircraft.Unguided missiles can be carried in, or under, any convenient part of a fighter; in fact, a number GUNS FOR FIGHTERS of automatic magazine-fed launchers for folding-fin, rotation-stabilized missiles have been developed in America and installed in such aircraft as the Skyraider (wings) and Scorpion (nose).Guided weapons are generally carried externally, involving an increase in drag. Since the configuration of most fighters pre-cludes stowage under the fuselage, the only space available is under the wings, with a consequent reduction in the fighter'srate of roll. Air-launched missiles are discussed on p. 114 et seq. The installation of efficient gun armament is probably at leastas difficult as is that of self-propelled missiles. Some of the more obvious factors which a gun installation has to take into account arethe following: proper ammunition feed under all conditions of temperature, vibration and acceleration loading; muzzle blast andflash; recoil; discharge of exhaust gas, spent cases and links; and integration with sighting equipment and radar. The aircraft structure around gun muzzles is subjected to rapidand violent pressure pulsations of a type which may be expected to cause fatigue problems. Furdiermore, the muzzle blast, to-gether with entrained cooling air, creates a region around the muzzles in which the local flow opposes the slipstream; althoughthis is rarely of importance from the point of view of stability or control of the aircraft, it is worth noting that, if this region is nearengine intakes, great care has to be exercised if engine performance is not to be impaired. The flash from high-velocity cannon mayextend for several feet and, while hardly dazzling in daylight, is capable of destroying night vision unless the armament is sosituated that the flash cannot be seen by the aircraft crew, either directly or by reflection. A nose installation of two Oerlikon 30 mm guns mounted on their sides. Separate chutes can be seen for links (A) and cases (B).
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