航空術(shù)語詞典Dictionary of Aeronautical Terms 中

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

magnetic bearing (navigation). The direction to or from a radio transmitting station measured relative to magnetic north.
magnetic brake (electric motor component). A type of friction brake that automatically releases when current flows through the motor windings. As soon as current to the motor is shut off, a spring forces a stationary friction disk against a disk that rotates with the motor armature. The friction prevents the armature turning. An electromagnet pulls the stationary disk away from the rotating disk when current flows in the motor.
magnetic bubble memory (digital computers). A method of storing information for use in a digital computer. Tiny areas of magnetism can be formed in a thin film of magnetic garnet crystal. These tiny areas, or bubbles, can be moved about within the film to change the logic conditions they represent. Magnetic bubble memory allows an extremely large amount of digital information to be stored in an exceedingly small area.
magnetic chuck. A special work surface used with certain types of metal-machining tools. An electromagnetic force holds the material being machined tightly to the surface.
magnetic circuit. The complete path in an electrical machine that is followed by lines of magnetic flux. Lines of flux leave the north pole of the magnet, flow through all the circuit components, and re-enter the magnet at its south pole.
In a motor or generator, the magnetic circuit is made up of the pole shoes, the armature core, the field frame, and the air gaps between the pole shoes and the armature
magnetic circuit breaker. An electrical component that opens a circuit any time excessive current flows. A magnetic field is produced by current flowing through the circuit breaker, and the strength of the field is proportional to the amount of current. When more current flows through the circuit breaker than it is rated to carry, the magnetic field becomes strong enough to snap open a set of contacts and break, or open, the circuit.
magnetic course (navigation). A desired flight path referenced from magnetic north. A true course measured on a navigational chart is referenced to the geographic north pole but a magnetic compass points to the magnetic north pole. The angular difference between a true course and a magnetic course is called variation.
magnetic deviation (navigation). A form of compass error caused by local magnetic fields in the aircraft interacting with the magnetic field of the earth. Deviation error is minimized by counteracting the interfering magnetic fields by adjusting small compensating magnets that are built into the compass housing. This compensating procedure is called “swinging the compass.” Deviation error differs with each heading of the aircraft.
magnetic-drag tachometer. An instrument used in an aircraft to show the rotational speed of the engine crankshaft. A flexible shaft, or cable, turned at one-half crankshaft speed, spins a permanent magnet inside the tachometer.
An aluminum drag cup rides over the spinning magnet, but does not touch it. A pointer shaft is mounted on the center of the cup, and the tachometer pointer is pressed onto the end of the shaft. A flat, coiled hairspring attached to the shaft holds the cup against a stop so the pointer rests on zero when the magnet is not spinning.

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