Efficiency—Output Input
Efficiency (of an aeroplane as distinct from engine and propeller)—
Lift and Velocity
Thrust (= aeroplane drift)
Efficiency, Engine—Brake horse-power
Indicated horse-power
Efficiency, Propeller—
Thrust horse-power
Horse-power received from engine
(= propeller drift)
NOTE.—The above terms can, of course, be expressed in foot-pounds. It is then only necessary to divide the upper term by the lower one to find the measure of efficiency.
Elevator—A controlling surface, usually hinged to the rear of the tail-plane, the operation of which turns an aeroplane about an axis which is transverse to the direction of normal horizontal flight.
Empennage—See “Tail-plane.”