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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dissolved acetylene gas. Acetylene gas which has been dissolved, or absorbed, in liquid acetone. Acetylene gas becomes unstable when it is held under pressure of more than about 15 psi, but if it is dissolved in acetone, it can be safely held under a pressure of more than 250 psi. dissymmetry of lift (helicopter flight condition). The unequal lift produced across the rotor disk of a helicopter moving through the air. The advancing blade, the blade whose tip is moving in the same direction the helicopter is flying, has a speed equal to its own speed plus the speed of the helicopter. The retreating blade, the blade whose tip is moving in the opposite direction, is traveling at a speed equal to its own speed less the speed of the helicopter. Since aerodynamic lift is determined by the speed of the airfoil through the air, the advancing blade produces more lift than the retreating blade. Dissymmetry of lift is compensated by allowing the blades to flap. As the lift produced by the advancing blade increases, it flaps upward, decreasing its angle of attack, and thus its lift. As the lift produced by the retreating blade decreases, it flaps downward, increasing both its angle of attack and the lift it produces. distance available (ALD). Available landing distance is that portion of a runway available for landing and roll-out for aircraft cleared for land-and-hold-short operation (LAHSO). This distance is measured from the landing threshold to the hold-short point. distance measuring equipment. See DME. distillate. A liquid obtained by condensing the vapors boiled off a material when it is heated in the process of distillation. distillation. A process by which components of a liquid mixture are separated. Crude oil, for example, is a source of many hydrocarbon fuels and lubricants which are obtained by the process of distillation. The crude oil is heated to a specific temperature and some vapors are driven off, and these vapors are cooled until they condense into a liquid. The temperature of the oil is increased and more vapors are driven off and condensed. Butane, gasoline, kerosine, diesel fuel, furnace oil, lubricating oil, and tar all have different boiling points and are all produced by distilling crude oil. distilled water. Water that has been purified by distillation. The water is boiled to convert it into water vapor, and the vapor is condensed into liquid water. Minerals and other contaminants in the liquid water do not stay with the water when it is changed into a vapor. They are removed by the process of distillation. distress (air traffic control). A condition of being threatened by serious and/or imminent danger, and of requiring immediate assistance. distress frequencies (radio communications). Frequencies for radio transmission recognized by most nations as universal frequencies for distress, or emergency, purposes. In the low-frequency band, 500 kilohertz is the distress frequency. In the VHF (very high frequency) band, it is 121.5 megahertz, and in the UHF (ultra high frequency) band, it is 243.0 megahertz. These distress (or emergency) frequencies are continuously monitored by many military and commercial radio operators. |
