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

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

substandard. The quality of an object that is less than can be considered normal or acceptable.
substitute. To use one material or object to take the place of something else. Plans and specifications often call for a certain type of material to be used. But if this particular material is not available, another material may be used in its place. The material used in place of the one specified is a substitute material.
substrate. The wafer of semiconductor material on which the components of integrated circuits are diffused and deposited.
subsystem. A small system inside a larger system. Each subsystem has a job it must perform for the main system to operate properly.
subtraction (mathematics). The mathematical process in which the value of one number is taken from the value of another.
subtrahend (mathematics). The number in a subtraction problem that is to be subtracted.
suction. A term commonly used for a negative pressure, or a pressure below atmospheric pressure. The terms suction and vacuum are both used to mean a negative pressure.
suction relief valve (pneumatic system component). A component that holds a constant and steady suction, a pressure lower than that of the atmosphere, on a system. Some gyroscopic instruments used in an aircraft are operated by air pulled into the instrument case by a suction produced by an engine-driven vacuum pump.
A suction relief valve in the line between the pump and the instrument case has a spring-loaded poppet that remains closed until the pressure becomes low enough to allow outside air pressure to force the poppet off its seat, then outside air is taken into the pump through the valve, rather than through the instrument case. This air entering the system holds the pressure inside the instrument case at the value for which the suction relief valve is set.
sudden stoppage (engine operating condition). A condition likely to cause internal damage to an aircraft engine. An engine is said to have a sudden stoppage if it comes to a complete stop within one revolution of the crankshaft.
sulfating (battery condition). A condition in a lead-acid storage battery in which both the positive and negative plates are covered with a hard deposit of lead sulfate. When a lead-acid battery discharges, the active material on both its plates changes into lead sulfate, which can be removed by recharging the battery. But if the battery is allowed to stand in a discharged state for a long period of time, the sulfate hardens and is difficult, if not impossible, to remove by normal recharging.
sulfur. A pale yellow, nonmetallic chemical element. Sulfur’s symbol is S, its atomic number is 16, and its atomic weight is 32.064. Sulfur, also spelled sulphur, is extremely important in the manufacture of commercial and industrial compounds and is found in its free state in underground beds along the Gulf coast of Texas and Louisiana.
sum (mathematics). The answer to an addition problem when two or more numbers are added together. In the problem 2 + 4 = 6, the number 6 is the sum.

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