时间：2011-03-11 23:18来源：蓝天飞行翻译 作者：航空 点击：次
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reverse-current relay (generator control device). A normally open, magnetically closed switch in the output circuit of a DC generator, between the generator and the battery. When the generator voltage is lower than that of the battery, a spring holds the reverse-current relay contacts open, and the generator is not connected to the battery. As soon as the generator voltage rises above that of the battery, an electromagnet in the relay closes the contacts and connects the generator to the battery. The more current flowing from the generator to the battery, the tighter the contacts are pulled together. When the generator voltage drops below that of the battery, reverse current flows from the battery to the generator. When reverse current flows, the magnetic field holding the contacts closed is cancelled, and a spring pulls the relay contacts open. This disconnects the generator from the battery. If a DC generator control circuit did not incorporate a reverse-current relay, the battery would discharge through the generator when the generator voltage was lower than that of the battery. reverse-flow combustor (gas turbine engine component). A type of turbine engine combustor in which the air flowing from the compressor follows an S-shaped pattern and enters the combustor at its rear end. As the air flows forward through the combustor, fuel is sprayed into it and burned. The burning fuel heats and expands the air. After the hot gases leave the combustor, they complete the S-turn and flow rearward, through the turbine. Reverse-flow combustors allow the engine to be shorter than it could be if straight-through combustors were used. reverse-polarity welding. DC electric arc welding in which the electrode is positive with respect to the work. reversible-pitch propeller (airplane propeller). An aircraft propeller whose blades can be moved to a pitch angle that produces reverse thrust. Reversible-pitch propellers are used to decrease the length of the landing roll needed by the airplane. revision block (aircraft drawing). An area on an aircraft drawing, usually in the lower right-hand corner, where a record is made of the number of the revision of the part shown in the drawing. revolved section (aircraft drawing). A detailed view of a part cut from one of the main views of the drawing and revolved to show its cross section. Reynolds number (fluid mechanics). A dimensionless number used to determine the flow characteristics of a fluid passing over a body. Reynolds number (RN) is determined by the velocity of the fluid, the distance the fluid travels over the body, and the kinematic viscosity of the fluid. Kinematic viscosity is the absolute viscosity of the fluid divided by its density. RN = Vx / ν V = Velocity in feet per second x = Distance from leading edge in feet n = kinematic viscosity in square feet per second RF energy. Radio frequency energy. Electromagnetic energy with a frequency high enough that it will radiate from any conductor through which it is flowing. |
