时间：2011-03-11 23:18来源：蓝天飞行翻译 作者：航空 点击：次
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stroboscopic tachometer. A device used to measure rotational speed by the use of a stroboscopic light. A brilliant light which flashes at a controlled rate is shone on the rotating object. When the light is adjusted to flash at the same rate the object is rotating, the object appears to stand still. The flash rate of the light is calibrated in terms of revolutions per minute (RPM). stroke (reciprocating engine parameter). The linear distance the piston moves inside the cylinder from the top to the bottom. strontium. A soft, silvery, easily oxidized, metallic chemical element. Strontium’s symbol is Sr, its atomic number is 38, and its atomic weight is 87.62. Finely divided strontium ignites spontaneously in air. Strontium is used in the manufacture of pyrotechnic devices. stud (fastening device). A threaded fastener used to attach components to an engine crankcase or other type of casting. A stud used to fasten a cylinder to a cast aluminum alloy crankcase has threads on both ends. The threads that screw into the soft aluminum crankcase are coarse, and the threads on which a nut is screwed to clamp the cylinder base to the crankcase are fine. stuffing box. A box through which a sliding or rotating shaft passes. The stuffing box contains packing material that can be compressed around the shaft to prevent liquid or gas leaking past the moving shaft. Styrofoam. The registered trade name for an expanded (full of bubbles), rigid polystyrene plastic material. subassembly. An assembly of components that is part of a larger device. A wing is a subassembly of an airplane. subatomic particles. Particles smaller than an atom. Electrons, protons, and neutrons are sub-atomic particles. subfreezing temperature. Temperature lower than that needed to cause water to freeze. sublimation. The procedure in which a solid material changes directly into a vapor or a vapor changes into a solid without becoming a liquid in the process. submerged-arc welding. A form of electric arc welding in which a bare rod is used as the electrode. The rod is covered with granulated flux that melts in the arc and flows out ahead of the weld to prevent the formation of oxides in the bead. subrefraction (radar technology). Less than normal bending of a radar beam, resulting from abnormal vertical gradients of temperature and/or water vapor. subscript. A number or letter written to the right of, and partially below, an abbreviation or a number. In gas turbine engine operation, the symbol PAm identifies ambient pressure. “P” stands for pressure, and the subscript “Am” tells that this pressure is ambient pressure. The chemical formula for water is H2O. The subscript “2” indicates that two atoms of hydrogen unite with one atom of oxygen to form one molecule of water. subsidence (meteorology). A descending motion of the air in the atmosphere over a rather broad area. subsonic flight (aircraft flight). Flight of an aircraft in which all the air passing over the aircraft structure is moving at a speed slower than the speed of sound. |
