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

時間：2011-03-11 23:13來源：藍(lán)天飛行翻譯 作者：admin 點擊：次

A free-running multivibrator has no stable condition, and because of this, it is called an astable (no stable condition) oscillator.
free turbine (gas turbine engine component). A turbine or stage of turbines in a gas turbine engine that is not used to drive the compressor in the gas-generator section of the engine.
A free turbine may be used to drive the reduction gears for the propeller in a turboprop engine, or the transmission and a rotor of a helicopter. Free turbines are also used in industrial turbine engines to drive pumps or generators. Free turbines are sometimes referred to as free power turbines.
free wheeling unit (helicopter component). A component part of the transmission or power train of a helicopter which automatically disconnects the main rotor from the engine when the engine stops or slows below the equivalent RPM of the rotor.
freezing. The process in which a liquid is changed into a solid by the removal of heat energy. When enough heat energy is removed from liquid water, it freezes, or turns into solid water (ice).
freezing level (meteorology). The level in the atmosphere at which the temperature is 0°C (32°F).
freezing point. The temperature at which a liquid changes into a solid. In petroleum specifications, freezing point is the temperature at which solids, such as wax crystals, separate from a hydrocarbon fuel as it is cooled.
French fell seam (machine-sewed fabric seam). A type of machine-sewed seam in which the edges of the two pieces of fabric are folded together, and a double row of stitches passes through four thicknesses of the material.

Freon. The registered trade name for a fluorinated hydrocarbon compound used as a refrigerant and a fire extinguishing agent. There are a number of Freon compounds identified with numbers. Each compound having different characteristics.
Freon-12 has been the most commonly used refrigerant in aircraft air conditioning systems, but because of environmental considerations it is being phased out and replaced by R-134a which is more environmentally friendly.
frequency. The number of complete cycles of a recurring event that take place in one unit of time.
frequency converter (electronic circuit). A circuit which changes the frequency of alternating current. Alternating current with a frequency of 1,000 hertz, for example, can be changed to 200 hertz by combining it with an AC signal having a frequency of 1,200 hertz.
When alternating currents having these two frequencies are combined, or mixed, two more alternating currents are produced: one having a frequency which is the sum of the two, 2,200 hertz, and the other a frequency which is the difference between the two — in this case, 200 hertz, the desired frequency.
frequency divider (electronic circuit). An electronic circuit whose output has a frequency that is an exact divisor of the frequency at the input. If a signal of 100 kilohertz is placed on the input of a frequency divider that divides by two, the frequency at the output will be 50 kilohertz.

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