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Deck—A main aeroplane surface. The term is used generally in describing biplanes; as the upper deck, and the lower deck; or with aeroplanes of many decks.
Demountable—A type of construction which permits a machine to be easily taken apart for transportation.
Derrick—A tower-shaped structure in which a weight is raised and allowed to fall to give starting impetus to an aeroplane.
Dihedral—That form of construction in which the wings of an aeroplane start with an upward incline at their junction with the body of the machine, instead of stretching out on a level.
Dirigible—The condition of being directable, or steerable: applied generally to the balloons fitted with propelling power, or airships.
Double Rudder—A rudder composed of two intersecting planes, one vertical and the other horizontal, thus enabling the operator to steer in any direction with the one rudder.
Double-Surfaced—Planes which are covered with fabric on both their upper and lower surfaces, thus completely inclosing their frames.
Down-Wind—Along with the wind; in the direction in which the wind is blowing.
Drift—The recoil of an aeroplane surface forced through the air: also the tendency to float in the same direction as the wind.