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
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universal joint. A type of shaft coupling that allows one shaft to drive the other, even if the two shafts are not in perfect alignment. A universal joint has a double hinge, with the axes of the two hinges at right angles to each other. universal motor. A form of series-wound electric motor that operates equally well on alternating current or direct current. A universal motor has a commutator on its armature, and armature current is fed into the commutator through brushes. universal propeller protractor. A precision protractor that can be read to one tenth of a degree. Universal propeller protractors are used to check and set the pitch of propeller blades and to measure the amount of movement of aircraft control surfaces. universal time. Solar time at the prime meridian. Solar time is the time based on the rotation of the earth about the sun, and the prime meridian is the meridian of longitude that passes through the Royal Observatory at Greenwich, England. Universal time is known also as Greenwich mean time (GMT) and Zulu time. unleaded gasoline (reciprocating engine fuel). A fuel for reciprocating engines that does not contain any tetraethyl lead (TEL). See TEL. unlimited ceiling (meteorology). A clear sky or a sky cover that does not meet the criteria for a ceiling. unloading valve (hydraulic system component). A pressure control valve used in an aircraft hydraulic system to unload the engine-driven pump when the system pressure reaches a predetermined value. The unloading valve traps the pressure in the pressure manifold, where it is held by the accumulator, and routes the output of the pump back to the reservoir. When the pressure in the manifold drops to a lower predetermined value, the unloading valve directs the pump output back into the pressure manifold. An unloading valve is also called a system pressure regulator. See system pressure regulator. unscheduled maintenance. Maintenance performed on an aircraft as a result of a problem discovered in the course of normal operation. Scheduled maintenance is maintenance performed according to a predetermined plan or schedule. unstable air (meteorology). A mass of air whose temperature lapse rate, the change in temperature as the altitude changes, is greater than that of the air surrounding it. When unstable air is forced upward by flowing up the side of a mountain, for example, it will continue to move upward, increasing its speed as it goes up. This causes updrafts in the air. Cumulus clouds form at the top of a column of rising unstable air. unusable fuel (aircraft specification). Fuel in an aircraft fuel system that will not flow to the fuel metering system when the aircraft is in its normal flight attitude. This fuel is also called residual fuel. The weight of unusable fuel is included in the empty weight of the aircraft. updraft (meteorology). A localized upward current of air. updraft carburetor (reciprocating engine component). A type of carburetor that mounts below the intake manifold of a reciprocating engine. All of the air flowing into the engine flows upward through the venturi. |
