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

時(shí)間：2011-03-11 23:18來源：藍(lán)天飛行翻譯 作者：航空 點(diǎn)擊：次

press brake (production sheet-metal tool). A form of sheet-metal bending tool in which a long, straight male die whose bottom edge has the correct bend radius is pressed down onto a sheet of metal placed over a female die containing a long V-shaped groove. The male die is usually forced down by energy stored in a large flywheel.
press fit. An interference fit between machine parts. The hole into which a part is to fit is slightly smaller than the part itself, and the two can be assembled only by pushing the part into the hole with a press.
press-to-test light (indicator light). A type of indicator light used in an aircraft. The bulb may be tested by pressing on the top of the light fixture to complete a circuit to ground. If the bulb is good, the light will illuminate.
pressure. A measure of force applied uniformly over a given unit of surface area. Pressure is normally expressed in such terms as pounds per square inch or grams per square centimeter.
pressure altimeter. Another name for a pneumatic altimeter. See pneumatic altimeter.
pressure altitude. The altitude in standard atmosphere at which the pressure is the same as the existing pressure. Because a pneumatic altimeter operates solely on pressure, pressure altitude is the uncorrected altitude indicated by an altimeter when its barometric scale is adjusted to standard sea-level pressure of
29.92 inches of mercury, or 1013.2 millibars.
pressure carburetor (reciprocating engine component). A fuel metering device that meters fuel to a reciprocating engine on the basis of the mass of air flowing into the engine. The pressure forcing the fuel through the metering jet is determined by the difference between two air-metering forces: the low pressure produced at the throat of a venturi, and the high pressure of the air as it rams into the carburetor. These two air pressures act on a diaphragm to control a fuel pressure regulating system that varies the pressure drop across the fuel metering jet as a function of the mass of air flowing into the engine.
pressure casting. A method of casting metal parts in which molten or plastic metal is forced into permanent molds under pressure.
pressure cooling (reciprocating engine cooling). A method of air-cooling an engine in which the cylinders are enclosed in tight-fitting shrouds. The cowling is divided into two compartments by baffles and seals, with half of each cylinder in each compartment. Ram air is directed into one compartment, and the pressure in the other is decreased by air flowing over a flared exit or adjustable cowl flaps. The pressure difference across the cylinders causes cooling air to be drawn through the fins to remove the unwanted heat.
pressure-demand oxygen system. A type of oxygen system used by aircraft that fly at very high altitude. This system functions as a diluter-demand system below about 40,000 feet. Above this altitude, the regulator furnishes the mask with 100% oxygen under pressure to force the oxygen into the lungs, rather than depending on the low pressure produced when the wearer of the mask inhales to pull in the oxygen. See diluter-demand oxygen system.

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