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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Some gas turbine engines use additional stages of turbines to extract energy from the hot gases to drive such devices as fans, propellers, rotors, generators, or pumps. Gas turbine engines are far superior to reciprocating engines, with regard to their weight-to-horsepower ratio. gas welding. A method of joining metals by melting them and allowing the molten metal from the two pieces to flow together. The heat used to melt the metal is provided by burning a mixture of fuel gas and oxygen. The two most generally used fuel gases are acetylene and hydrogen. gate (electrode of a semiconductor device). The electrode in a silicon controlled rectifier (SCR), triac, or field effect transistor (FET), to which trigger pulses of electrical energy are applied to cause a flow of electrons between the other electrodes. gate hold procedures (aircraft operation). Procedures at selected airports to hold aircraft at the gate or other ground locations whenever departure delays exceed or are anticipated to exceed five minutes. gate-type check valve. A type of one-way valve that uses a swinging gate, or flapper, to control the flow of fluid. Gate-type check valves are used in multiengine aircraft vacuum systems to isolate one of the pumps if it should fail. gauss. The unit of magnetic flux density in the centimeter-gram-second system of metric measurement. One gauss is a flux density of one line of flux (one maxwell) per square centimeter. Gay Lussac’s law. See Charles’s law. GCA (ground controlled approach) (air traffic control). A radar approach system operated from the ground by air traffic control personnel transmitting instruction to the pilot by radio. The approach may be conducted with surveillance radar (ASR) only or with both surveillance and precision approach radar (PAR). Usage of the term GCA by pilots is discouraged except when referring to a GCA facility. Pilots should specifically request a PAR approach when a precision radar approach is desired or request an ASR, or surveillance, approach when a nonprecision radar approach is desired. gear. A special wheel with notched teeth on its periphery. Gears transmit power from one shaft to another without slippage by meshing the teeth of the gear on one shaft with the teeth of the gear on the other. Gears are used to reverse the direction of shaft rotation and to gain mechanical advantage. gear and pinion mechanism. A mechanical force amplifying system that uses two gears of different sizes. The smaller gear, the pinion, meshes with and turns faster than the larger gear. The ratio between the number of teeth on the pinion and the number on the large gear determines the mechanical advantage of the mechanism. gear backlash. The amount of clearance between the teeth of two meshed gears. It is very important that the correct amount of gear backlash be maintained when meshing gears. If there is no backlash, the teeth cannot be properly lubricated, and the gears will wear excessively. If there is too much backlash, the load is not properly transmitted from one tooth to the other. |
