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Dacron. The registered trade name for polyester fibers manufactured by the E. I. DuPont de Nemours & Company. Cloth woven from Dacron fibers is used as a covering material for aircraft structure.
dado head (woodworking tool). A multibladed circular saw having two blades mounted on an arbor with a chipper between them. A dado head is used to cut a flat-bottomed groove in wood.
dado plane (woodworking tool). A hand plane with a narrow blade. Dado planes are used to cut flat-bottom grooves in wood.
Dalton’s law. The gas law which states that there will always be the same number of molecules of gas in a container when the gas is held at a uniform pressure and temperature. Dalton’s law explains the partial pressure of the gases which make up the air in our atmosphere.
damp, or dampen (verb). To decrease the amplitude of an oscillating or reciprocating motion.
damped oscillations. Oscillations whose amplitude decreases with time. The oscillations of an airplane that has positive static stability and positive dynamic stability are damped oscillations.
damper, or dampener (vibration damper). A device used to dampen vibrations or oscillations or to bring a vibrating body to a stop with a minimum of oscillations.
damper-type fire valve (combustion heater component). An automatic valve that closes off the air supply to a combustion heater if a fire or over-temperature condition occurs.
A spring-loaded, butterfly-type damper valve is installed in the air inlet duct to the heater, and it is held open by fusible links. If an over-temperature condition occurs, the links will melt, and the damper valve will shut off the air to the heater. The fire will go out.
damper valve. A butterfly-type valve in an air duct. This valve is a round plate mounted on a shaft sticking through the duct. When the damper is open, it is parallel with the duct, and the air flows around it. When it is closed, the valve plate is almost perpendicular to the duct, and no air can flow past it.
danger area (ICAO). An airspace of defined dimensions within which activities dangerous to the flight of aircraft may exist at specified times.
Note: The term “danger area” is not used in reference to areas within the United States or any of its possessions or territories.
Daniell cell (electrical energy). A form of standard cell used for measuring voltage by comparison. A Daniell cell produces an accurate voltage of 1.1 volts with a copper electrode in a copper sulfate solution and a zinc electrode in a zinc sulfate solution. The two solutions are separated by a porous membrane.
dark current (photoelectric device). The current which flows in a photoelectric device, such as a photodiode or phototransistor, when no light is falling on the light-sensitive junction.
Darlington amplifier (electronic circuit). A type of transistor amplifier in which two bipolar transistors are connected in such a way that the emitter of the input transistor is connected directly to the base of the output transistor. The collectors of both transistors are connected together. A Darlington amplifier is a double emitter-follower amplifier.
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