时间：2011-03-11 23:11来源：蓝天飞行翻译 作者：admin 点击：次
|
Davis wing (aerodynamics). A relatively thick, narrow-chord wing used on some airplanes. A Davis wing has a relatively low drag and a stable center of pressure, and it develops lift at low angles of attack. The B-24 Liberator bomber of World War II used the Davis wing. DC electricity (direct current electricity). Electricity in which the electrons flow in the same direction all of the time. Electricity produced by chemical cells, solar cells, and thermocouples is DC electricity. DC alternator. The electrical generation device that has replaced the generator on practically all modern automobiles and light airplanes. Excitation current from the aircraft battery flows through the voltage regulator into the rotor coil through brushes and slip rings to produce a multiple-pole rotating magnetic field. This rotating field cuts across the three-phase output windings in the stator to produce an alternating current whose amount is determined by the alternator speed and the amount of excitation current supplied by the voltage regulator. A six-diode, three-phase rectifier changes the AC into DC before it leaves the alternator. DC amplifier (electronic amplifier). An electronic amplifier which can amplify direct-current signals and alternating current signals having a very low frequency. DC generator (electrical machine). An electrical machine that converts mechanical energy into DC electricity. A conductor is moved through a magnetic field, and the mechanical energy used to move the conductor is changed into electrical energy. Almost all generators of this type produce alternating current, and some type of rectifier is used to change the AC into DC before it leaves the generator. DC motor (electrical machine). An electric motor that operates on direct current. DC power. The product of current and voltage. DC power is measured in watts. D-check. See maintenance checks. dead. A term used in technology to mean the absence of motion. deadbeat. The condition of a free-swinging device when it comes to rest without overshooting its at-rest position. A pointer on a highly damped measuring instrument is said to be deadbeat when it changes its indication from one point to another without overshooting its final indication. It does not oscillate back and forth over its final position. dead center (machine tool). A pointed device mounted in the tailstock of a lathe. The dead center is used to support the work being turned. The dead center does not turn with the work. dead-center position (reciprocating engine). The position of the piston in a reciprocating engine in which the wrist pin, the crank pin, and the center of the crankshaft are all in a straight line. There are two dead-center positions: TDC (top dead-center) and BDC (bottom dead-center). When the crankshaft is in either of the dead-center positions, the piston has stopped moving and is reversing its direction of travel. dead engine (aircraft engine). An engine which has been shut down in flight and is no longer operating. |
