All About Engines

230 All About Engines unnecessary and economising weight and space. They are opened by rocking levers operated from a cam shaft in the usual way. Every ,possible device is employed to reduce weight. The crank cases are of aluminium alloy, and so are the pistons. The water jackets are of thin copper or aluminium. The con- necting rods are of steel, “ drop-forged ” in the shape of an H girder, tapering towards the upper end, giving the maximum strength with the minimum weight. Wherever metal is not needed it is cut away or scooped out, involving the most minute and exact calculations and requiring the most skilful workman- ship. In war time cost is of no consequence ; men are not content to proceed a step at a time ; they are rarely satisfied with a small improvement; if there is any advantage to be gained beyond that possessed at the moment, it must be pursued with- out a moment’s delay. What wonderful things these aeroplane engines are! Here is one with six cylinders, which two men can lift, capable of giving 120 horse-power! There is another, V-pattern, with twelve cylinders arranged in six pairs, not beyond the capacity of four men to lift, and yet capable of being coaxed up to 300 horse- power, or of performing work at the rate of 9,900,000 ft.-lb. per minute ! The crank shaft rotates 1,000 times a minute. Six times in every revolution does an explosion speed the shaft on its way. There are, therefore, 6,000 explosions every minute, every one timed exactly, so that they occur at equal intervals and with a regularity which is astounding.