The Aeroplane Speaks. Fifth Edition

=Displacement=--Change of position. =Drift= (of an aeroplane as distinct from the propeller)--The horizontal component of the reaction produced by the action of driving through the air a surface inclined upwards and towards its direction of motion plus the horizontal component of the reaction produced by the "detrimental" surface plus resistance due to "skin-friction." Sometimes termed "head-resistance." =Drift, Active=--Drift produced by the lifting surface. =Drift, Passive=--Drift produced by the detrimental surface. =Drift= (of a propeller)--Analogous to the drift of an aeroplane. It is convenient to include "eddies" and "cavitation" within this term. =Drift, to=--To be carried by a current of air; to make leeway. =Dive, to=--To descend so steeply as to produce a speed greater than the normal flying speed. =Dope, to=--To paint a fabric with a special fluid for the purpose of tightening and protecting it. =Density=--Mass of unit volume; for instance, pounds per cubic foot. =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. [8] =Empennage=--See "Tail-plane."