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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

hard-facing. A method of increasing the hardness of the face of a steel tool to keep it from being worn away in normal use. Hard-facing is done by welding, plating, or spraying a hard material, such as a carbide, on the surface of the tool.
hard landing (aircraft operation). An airplane landing in which enough forces have been transmitted into the structure to have likely caused damage.
hardness. The ability of a material to resist being scratched. Hardness is measured using the Mohs scale, which rates the hardness of a material by comparing it with ten minerals that have been given Mohs hardness values from one to ten.
These minerals range from talc, whose Mohs hardness is one, through gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, to diamond. Diamond has a Mohs hardness of ten.
hardness test. A test that can be made of either metallic or non-metallic materials to determine their physical condition. A cone- or a ball-shaped tool is forced into the surface of the material, and the diameter or depth of the penetration caused by a given amount of force is measured. The diameter or depth of the penetration is related to the hardness and the strength of the material. See Rockwell hardness tester and Brinell hardness test.
hard rubber. Rubber that has been vulcanized under high temperature and pressure to make it hard. Hard rubber is used as an electrical insulator and for the handles of many different types of tools.
hardware. A general term for all of the small components, such as nuts, bolts, screws, and washers used to assemble an aircraft or aircraft engine.
hardware (computer operation). The physical equipment used in computer operation.
hardwood. Wood from a broadleaf tree that sheds its leaves each year.
hard X-rays. X-rays that have a great deal of penetrating power. The penetrating power of X-rays is determined by the amount of voltage applied to the anode of the X-ray tube. The higher the voltage, the harder the X-ray (the greater its penetrating power).
harmonic. A vibration whose frequency is an even multiple of another vibration. The first harmonic of a 400-Hz vibration has a frequency of 400 Hz. The frequency of the first harmonic is the same as the fundamental frequency. The second harmonic has a frequency of 800 hertz, and the third harmonic has a frequency of 1,200 hertz.
harness (electrical). A bundle of wires routed through an aircraft structure, connecting electrical components to each other and to the power bus.
Hartley oscillator. A popular electronic oscillator circuit which uses a tapped coil in parallel with a capacitor to determine the frequency of the AC the circuit produces. Energy from the collector of a transistor, or the plate of a vacuum tube, passes through one half of the coil and induces a voltage in the other half.
This induced voltage is applied to the base of the transistor, or the grid of the vacuum tube, with a polarity that causes the circuit to oscillate, or produce alternating current.

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