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Aviation History
1913
1913 - 1306.PDF
THE LEWIS AIR-COOLED MACHINE GUN. THE recent demonstration arranged by the Birmingham Small Arms Co., Ltd., at Bisley, in connection with the Lewis automatic air-cooled machine gun, at which a large number of distinguished naval and military officers and others interested in aviation were present, brings again into prominence the important part that will be played by aerial craft in a war between Powers provided with aeroplanes and dirigibles. F'or ihe armament of such craft, the machine gun has inherent advantages over other weapons, but it is essential that the gun should be specially adapted for this class of work. It is important that it should be entirely self-contained, it should have li'tle weight, be readily dismantled and assembled and be capable of firing in any direction ; and since the time of engagement will probably be short, the projectile should be as destructive in its effects as possible. For use on aeroplanes, the weight, cumbrousness and recoil of a gun capable of discharging explosive projectiles render such at a •disadvantage compared with the machine which is capable of firing a large quantity of small ammunition at high speed, and hence for this form of aircraft the latter is preferable. It is claimed that in the Lewis air-cooled machine-gun, shown in the accompanying illustration, these qualities are exemplified. Its weight is 26^ lbs., it can be handled by one man, and fired in any position or direction, its recoil is negligible and the normal rate of firing is 500 rounds per minute, but this can be increased if desired up to 800 rounds per minute, and single rounds, or bursts of any number of rounds up to the full capacity of the magazine, which is 47 rounds, may be fired if desired. The magazine, M, which takes under two minutes to load by hand and considerably less by the aid of a special machine, uses the ordinary service ammunition, and may be charged in a few seconds. The facility with which the assembling ( or dismantlement of the gun can be carried out is a remarkable feature of the invention, the only tool required being the nose of an ordinary bullet, and it is stated that 1,500 rounds may be fired without dangerously overheating the barrel, which is air-cooled. The system of air-cooling employed is not the least of its good Trying the new Lewis automatic gun on a Grahame-White biplane at Bisley last week. The biplane, piloted by Mr. Marcus Manton, with Lieut. Stillirjgwerf in the seat underneath, manipulating the gun, Is just passing over the Clock Tower at Bisley before firing at the target just beyond. points, as thereby the necessity of carrying a supply of water for cooling purposes is entirely avoided. On the barrel, B, is a close-fitting sheath or jacket of aluminium with radiating longitudinal fins, surrounding which is a thin tubular steel casing, C, four inches in diameter. The tubular steel casing extends beyond the muzzle of the jacketted barrel, and as the gases of explosion emerge in a conical blast behind the bullet, they act as a kind of pump plunger inside this tubular extension, and suck currents of fresh cool air through the sector-shaped longitudinal passages along the exterior of the barrel. The air ejector thus formed at each discharge is most effective in cooling the barrel and is without mechanism or moving parts. During the first few hundred rounds the temperature rises rapidly until it has reached about 330° F., then more slowly until at the end of 1,000 rounds fired at full speed it does not exceed 440^ F., and under ordinary Service conditions will be much lower. The operating mechanism on the Lewis gun embodies several unique features, but one in particular should be mentioned—the use of a spring removed from the heat of the gun barrel. The gun is gas operated, that is to say, the energy required to load the breech and fire the cartridge is obtained by trapping some or the gases of the explosion through a small hole located a few inches from the muzzle. While the bullet is passing from this orifice to the muzzle, a period of about sVouth of a second, the gases deliver a blow to a piston, P, connected to the breech operating mechanism, and the energy thus stored as momentum in the moving mass serves to overcome the resistance represented by unlocking the breech, extracting and ejecting the cartridge case, turning the magazine and winding the spring that is subsequently to close the breech and fire the shot. This cycle of operations is repeated as many as 800 times a minute when the gun is working at its full speed, but the rapidity of fire can be regulated by changing the area of the orifice through which the gases are trapped, and by varying the tension on the clock-spring. It is apparent that the spring element in such a system must be 1332
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