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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performance number (reciprocating engine fuel specification). The antidetonation rating of a fuel which has a higher critical pressure and temperature than iso-octane (a rating of 100). Iso-octane which has been treated with varying amounts of tetraethyl lead is used as the reference. Aviation gasoline antidetonation ratings above 100 are called performance numbers. period (oscillation). The length of time needed for one complete cycle of oscillation to take place. periodic. Repeated at regular time intervals. Any event repeated regularly, with the same amount of time between the events, is said to be a periodic event. periodic inspection (aircraft inspection). A maintenance inspection that must be performed on a regular or recurring basis. Annual and 100-hour inspections are both periodic inspections. periodic table of chemical elements. A table listing all the chemical elements, arranged in horizontal rows and vertical columns to show the similarities of the properties of the elements. See Appendix 2. periodic vibration. A vibration having a regularly recurring waveform. Vibrations in the form of sine waves, square waves, or sawtooth waves are examples of periodic vibrations. peripheral equipment (computer equipment). Components in a computer system that may be attached to the computer. Peripherals consist of display units, storage devices, and such input/output devices as keyboards and printers. Permalloy. The registered trade name of an alloy of iron and nickel. Permalloy has a high magnetic permeability and is used in the manufacture of permanent magnets. permanent ballast (aircraft balance). A weight permanently installed in an aircraft to bring its center of gravity into allowable limits. permanent echo (radar return). Radar signals reflected from fixed objects on the earth’s surface; objects such as buildings, towers, and terrain that under certain conditions may be used to check radar alignment. Permanent echoes are distinguished from ground clutter by being definable locations rather than large areas. permanent magnet. A piece of magnetizable material, such as hard steel, that has been exposed to a strong magnetizing force. This force aligns the spin axes of the electrons surrounding the atoms of the material, and thus the magnetic domains within it. When the material is removed from the magnetic field, it is magnetized and the domains remain in alignment until a strong demagnetizing force is applied. permanent magnet speaker. The type of speaker used in small radios and tape players. The magnetic field in which the voice coil moves is produced by a small permanent magnet. permanent mold. A reusable metal mold, used for making complex castings. Castings made in permanent molds can be made thinner than those made by sand casting. permanent-mold casting. A casting made in a reusable metal mold. Many aircraft engine crankcases are cast in permanent-molds because their walls can be made thinner than similar walls made by sand casting. |
