时间：2011-03-11 23:13来源：蓝天飞行翻译 作者：admin 点击：次
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magnetism. A property possessed by certain materials that causes them to attract or repel other materials having this same property. Magnetism also causes electrical current to flow in a conductor when it is moved across the lines of magnetic flux extending out from the magnet. magnet keeper. A piece of soft iron placed across the poles of a horseshoe permanent magnet when the magnet is not in use. The permeability of the soft iron is much greater than that of the air between the poles, and by keeping the flux concentrated, the flux loss is minimized and the magnet is prevented from becoming demagnetized. magneto (reciprocating engine ignition system component). The source of high-voltage electrical energy, used to produce the spark to ignite the fuel-air mixture inside the cylinders of a reciprocating engine. A magneto contains a small alternating-current generator with a set of breaker points to interrupt the current the instant the spark is needed. Current produced by the AC generator flows through the primary winding of a step-up transformer, the magneto coil, and this current causes lines of magnetic flux to expand out across the many turns of wire in the secondary winding of the coil. When the breaker points open, the primary current immediately stops flowing, and the magnetic field instantly collapses, cutting across the secondary winding and producing a high voltage in it. A capacitor, installed across the breaker points, prevents arcing as the points open. A magneto also incorporates a distributor, or high-voltage selector switch, to direct the high voltage to the correct spark plug. magnetometer. An instrument used to measure and plot the strength and direction of the earth’s magnetic field. Magnetometers are often towed behind low-flying airplanes to find deposits of magnetic minerals by noting the change in the direction of the local magnetic field. These aerial surveys are referred to as MAD (magnetic anomaly detection) surveys. magnetomotive force (mmf). A force that produces a magnetic field. The magnetomotive force caused by current flowing in a coil of wire is determined by both the amount of current and the number of turns of wire. The gilbert is the unit of magnetomotive force, with one gilbert being the amount of mmf needed to cause one maxwell (one line of magnetic flux) to flow through a magnetic circuit having a reluctance (the opposition to the passage of magnetic flux) of one unit. One gilbert is also the amount of mmf produced by 0.7957-ampere turn. The constant 0.7957 is 10 divided by four π. magneto safety check (aircraft reciprocating engine operation check). A check made by the pilot of an |
