Drag: The component parallel to the relative wind of the total force on an aerofoil or aircraft due to the air through which it moves.
In the case of an airplane, that part of the drag due to the wings is called “wing resistance”; that due to the rest of the airplane is called “parasite resistance.”
Drift: See Drag. Also used as synonymous with “leeway,” q. v.
Drift meter: An instrument for the measurement of the angular deviation of an aircraft from a set course, due to cross winds.
Drip cloth: A curtain around the equator of a balloon, which prevents rain from dripping into the basket.
Droop: A permanent warp of an aerofoil such that the angle of attack increases toward the wing tips. (The opposite of “wash out.”)
Elevator: A movable auxiliary surface, usually attached to the tail, the function of which is to control the longitudinal attitude of an aircraft by rotating it about its lateral axis.
Empennage: The tail surfaces of an aircraft. Sometimes the word is limited to the fixed stabilizing portion of the tail—usually comprising the tail plane and vertical fin, to which are attached the elevator and rudders.
Entering edge: The foremost edge of an aerofoil or propeller blade.
Envelope: The outer covering of a rigid airship; or, in the case of a balloon or a nonrigid airship, the gas bag which contains the gas.