When an aircraft lands into the wind, its ground speed is its airspeed minus the speed of the wind. When it lands downwind, its speed over the ground is equal to its airspeed plus the speed of the wind.
DPDT switch (double-pole, double-throw electrical switch). A type of electrical switch with six terminals. It can be used to select any one of three conditions in two separate circuits. See double-throw switch.
DPST switch (double-pole, single-throw electrical switch). A type of electrical switch having four terminals. It can select either of two conditions in two separate circuits. See double-throw switch.
draft of a mold. The taper in the sides of a part cast in a mold. Draft makes it easy to remove the solidified part from the mold.
draftsman. A person who uses the process of mechanical drawing to make plans or sketches of machinery or structures.
A draftsman functions differently from an artist in that the draftsman uses templates and other mechanical devices to assure technical accuracy of the drawing. Drawings made by an artist are normally done freehand, and they convey thoughts and impressions, rather than objective representation of specific details.
drag (aerodynamic parameter). An aerodynamic force acting in the same plane as the relative wind striking an airfoil. Two basic types of drag act on an aircraft in flight: induced drag and parasite drag.
Induced drag is caused by the same factors that produce lift, and its amount varies inversely as the airspeed. As the airspeed decreases, the angle of attack must increase, and this increases the induced drag.
Parasite drag is caused by the friction of air moving over the structure, and its amount varies directly as the airspeed. The higher the airspeed, the greater the parasite drag.
drag (helicopter rotor blade movement). Fore-and-aft movement of the tip of a helicopter rotor blade in its plane of rotation.
drag brace (helicopter rotor component). An adjustable brace used to adjust the blade alignment of a semirigid helicopter rotor. Drag braces resist movement of the blade about its lead-lag hinge.
drag brace (landing gear component). A brace which supports an aircraft landing gear against loads trying to force the landing gear backward.
drag chute (aircraft operation). A small parachute attached to the rear of an airplane structure. The drag chute can be deployed (opened) after the airplane touches down on landing to help it slow down.
drag coefficient (aerodynamics). A dimensionless number used to find the amount of induced drag produced by an airfoil.
The drag coefficient is determined by the shape of the airfoil section and by the angle of attack. The coefficient of drag for any airfoil section increases as the angle of attack increases.
dragging brakes (aircraft brake malfunction). A condition in which the brakes do not fully release when pressure is removed from the brake pedal. The brakes are partially applied all the time, which causes excessive lining wear and heat.
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