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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keel (seaplane structure). The main longitudinal structural member extending along the center line of the bottom of a seaplane hull or float. keeper (magnet). A piece of soft iron placed across the poles of a magnet when the magnet is not being used. Magnetic energy is used to force lines of flux through the air between the poles, and the loss of this energy partially demagnetizes the magnet. The amount of energy used is determined by the reluctance (the opposition to the passage of the lines of flux) of the material between the poles. The soft iron keeper has a very low reluctance compared with air, and when the lines of flux travel through the keeper rather than through the air, less energy is used, and the magnet self-demagnetizes less. Kelvin bridge (resistance measuring instrument). A form of precision resistance-measuring instrument which is a modification of the Wheatstone bridge. A Kelvin bridge minimizes the effect of lead and contact resistance and is used for accurate measurements of low resistances. Kelvin temperature (absolute temperature). Temperature measured from absolute zero on a scale using the same divisions as are used in the Celsius system. Water freezes at 273°K and boils at 373°K. Kennelly-Heaviside layer (atmospheric layer). A layer of ionized particles in the atmosphere at an altitude of between 100 and 120 kilometers above the surface of the earth. Some radio waves cannot penetrate these particles, and they bounce back to the earth. The Kennelly-Heaviside layer is also called the Heaviside layer and the E-layer. kerf. The slit (the narrow slot, or opening) made by a saw blade as it cuts through wood, metal, or plastic, or by a cutting torch as it cuts through metal. kerosine (petroleum product). A light (specific gravity of about 0.8), almost colorless hydrocarbon liquid obtained from crude oil by the process of fractional distillation. Kerosine is used as a fuel for lamps and stoves and as a base for turbine engine fuel, and is commonly called coal oil. The name kerosine was originally spelled kerosene, but the “ene” ending wrongly implied that kerosine is made of unsaturated compounds (compounds having atoms bound together with more than one bond). To keep the spelling of the name from giving the wrong idea of the chemical composition of the material, the spelling was changed in 1957 by petroleum chemists to kerosine. Ketts saw (sheet-metal cutting tool). A power-operated saw used for cutting various thicknesses of metal sheet. The metal is cut with a small-diameter circular saw blade mounted in the head of this hand-held tool. Kevlar. A patented synthetic aramid fiber noted for its flexibility and light weight. It is to a great extent replacing fiberglass as a reinforcing fabric for composite aircraft construction. key (telegraph). A form of electrical switch used to break a continuous wave of radio-frequency alternating current into a series of dots and dashes for use in continuous wave (CW) radio transmission. The key allows the operator to send the dots and dashes in the sequence needed to transmit information by Morse code. |
