Page:Aircraft in Warfare (1916).djvu/259



The Lewis Machine Gun has features which render it especially suitable for employment as an aeroplane arm. These are in brief:— The absence of water jacket. The lightness obtained by the adoption of pressure in place of recoil actuation. The self-contained magazine.

The abandonment of the water jacket is effected by resort to direct air cooling, a gilled jacket being applied to the barrel; the problem is closely analagous to that of the air cooled petrol motor. In aeronautical fighting a machine gun is never required to work continuously for any length of time, and the problem under these conditions presents no difficulty: in other fields of usefulness the reverse is the case, and calculations given later in the present appendix give some idea of the real difficulty of the problem, the solution of which has been achieved by the inventor of this weapon. The advantage of pressure actuation in place of recoil actuation lies in the fact that if the former be adopted the total weight of the weapon can be designed to the minimum possible, whereas in a recoil actuated gun the mass of the portion which acts as " abutment " to the recoil mechanism has to be far greater than considerations of strength alone would warrant: thus the total weight is