航空術(shù)語(yǔ)詞典Dictionary of Aeronautical Terms 中

時(shí)間：2011-03-11 23:13來(lái)源：藍(lán)天飛行翻譯 作者：admin 點(diǎn)擊：次

droop compensator (helicopter turbine engine control). A linkage between the collective pitch control and the turbine speed governor that adjusts for the increased load the rotor places on the engine, as collective pitch is increased. The droop compensator prevents the rotor speed decreasing as the load is applied.
droop restraint (helicopter rotor system). A mechanical device that limits the amount the blades of a helicopter rotor can droop when the rotor is turning at a slow speed, and there is not enough centrifugal force to overcome the effect of gravity on the blades.
drop cloth. A piece of canvas or plastic used to cover the floor or objects on the floor when walls and ceilings are being painted. The drop cloth prevents paint from dripping on areas where it should not be.
drop forging. A method of forging steel parts by forcing semi-molten metal into a die by a heavy blow from a drop hammer. The grain structure of a drop-forged part gives it more strength than a cast part.
drop hammer. A large metalworking machine that uses heavy matched dies to form compound curves in sheet metal.
The sheet of metal to be formed is placed over a female die, and a heavy, matching male die is raised above it and dropped into the female die, forming the metal into the shape of the dies. Drop hammers are also used to forge semimolten metal in a die.
drop-out voltage (electrical relays). The minimum voltage needed to keep an electrical relay energized. When the voltage drops below this value, the relay automatically de-energizes.
Electromagnetism holds the relay energized, and a spring de-energizes it when the voltage producing the electromagnetism is below the drop-out voltage.
dropping resistor (electric circuit). A resistor in an electrical circuit used to drop voltage. For example, if a 12-volt light bulb is used in a 24-volt electrical system, a dropping resistor must be installed in series with the bulb to drop 12 volts. This allows only 12 volts across the bulb.
dropsonde (meteorology). An instrument pack and radio transmitter dropped by parachute from an aircraft to measure conditions of the atmosphere through which it passes. This information is continuously transmitted to meteorologists on the ground.
drop tank (fuel tank for military aircraft). An externally mounted fuel tank used on some military aircraft. Fuel is used from the drop tank first, and then the entire tank is dropped from the aircraft to get rid of the weight and the drag.
dross. The impurity that forms on the surface of molten metal. Dross is composed of the oxides produced by the reaction of oxygen in the air with the hot metal.
drum brake. A form of friction brake used on some airplanes. A drum brake is composed of two curved shoes which have a heat-absorbing friction material bonded to their outer surface. These shoes are pressed outward against the inside of a cylindrical drum that rotates with the wheel.
The brake is applied by hydraulic pressure or mechanical leverage forcing the shoes out against the drum, and a spring pulls them away from the drum when the brake pedal or handle is released.

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