The aeroplane motor is subject to far greater strains than the automobile motor is. Except during a race, one rarely runs the engine of an automobile at its maximum speed; the aeroplane motor, on the contrary, usually runs at full speed from the moment the aeroplane starts until the motor is shut off and begins to volplane down to the earth. It is true that you can regulate the aeroplane engine by the throttle to run from as low as three hundred revolutions a minute to as high as sixteen hundred; but except when testing the motor there is rarely any reason for slowing it up while in the air. The load that the propeller of an aeroplane carries is much less than the load that the shaft of an automobile carries, but, on account of the frail structure of the plane, the vibration is much more violent. A battle plane seldom weighs more than two thousand pounds, and a scouting machine of the Nieuport type tips the scales at not more than one thousand pounds. For these reasons aircraft require special kinds of motors. The V type is so called because the cylinders are set in the form of that letter; the rotary motor has the cylinders arranged in a circle like the spokes of a wheel, and it revolves on its shaft like the propeller. The rotary motor is used in scouting machines because it is light. The revolving engine also revolves on its shaft, but it has a great many more cylinders arranged side by side like the cylinders of an automobile engine. It is much heavier than the rotary type; it may have as many as thirty-two cylinders. Of course, a knowledge of the automobile engine was an aid to the prospective aviator; for, except in the process of cooling and the revolution of the cylinders, the principles of the automobile motor and those of the aeroplane are identical. At aviation schools the pupils went thoroughly into all those things and supplemented their knowledge by continually mounting and dismounting engines and examining their most intricate parts. The schools also kept on hand large aeroplane models, which the students took apart and put together again. In the classroom the prospective aviators studied the mathematics and the theory of aerodynamics. All this work was very important, for an aeroplane is such a nicely balanced machine that if it is not perfectly constructed mathematically it will not fly safely.