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. [8]
Empennage—See "Tail-plane."
Energy—Stored work. For instance, a given weight of coal or petroleum stores a given quantity of energy which may be expressed in foot-pounds.