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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I heavy hydrogen. Isotopes of hydrogen having one or two neutrons in the nucleus. Isotopes with one neutron are called deuterium 2H, and isotopes with two neutrons are called tritium 3H. heavy water. A compound of hydrogen and oxygen containing a larger proportion of deuterium (an isotope of hydrogen with one neutron in the nucleus) than normally occurs in water. hecto. The metric prefix that means one hundred (1 x 102). Hecto is used as a prefix, as in hectometers (100 meters), hectoliters (100 liters), etc. hedge-hop (aircraft flight). To fly an aircraft very near the surface of the earth. This flight is below the level of many obstructions on the ground, and the aircraft must be pulled up to pass over these obstructions. Hedge-hopping is both dangerous and illegal in all except a few special instances, such as agricultural application. heel of a bend (rigid fluid lines). The outside of a bend. The metal in the heel of a bend in rigid tubing has been stretched and is thinner than in other parts of the tubing. height above airport. See HAA. height above landing. See HAL. height above touchdown. See HAT. height-velocity envelope (helicopter operation). A chart produced by the manufacturer of a helicopter showing the conditions of airspeed related to height that produces conditions unsafe for an autorotative landing. Heliarc welding. A name used for inert-gas arc welding. There are two basic types of Heliarc welding: TIG (tungsten inert-gas) welding and MIG (metal inert-gas) welding. TIG welding uses a small-diameter nonconsumable tungsten rod as the electrode from which the arc jumps to the metal being welded. MIG welding uses a consumable soft steel rod as an electrode. This rod melts and adds metal to the molten pool to reinforce the weld. helical potentiometer (electrical component). A multi-turn potentiometer, or variable resistor. The resistance element is made in the form of a spiral, or helix, and the wiper is moved over the element by turning a multi-turn screw. Most helical potentiometers require ten turns of the screw to move the wiper from one end of the resistance element to the other. helical spline. A spline that twists, or winds, around the periphery of a shaft. Helical splines are used to change linear motion of the device that rides on the splines into rotary motion of the shaft on which the splines are cut. They are also used to change rotary motion of the shaft into linear motion of the device that rides on it. Helical splines are cut onto the shaft of some aircraft engine starter motors to move the starter gear into mesh with the flywheel gear (linear motion) when the starter shaft is spun (rotary motion). helical spring. A coil spring wound in the form of a spiral, or helix. Helical springs can be wound in such a way that they can absorb either tensile or compressive loads. Heli-Coil insert. The registered trade name for a special helical insert used to restore threads that have been stripped from a hole. The damaged threads are drilled out, and new threads are cut with a special oversize tap. A stainless steel coil of wire whose cross section is in the shape of a diamond is screwed into the hole and left there to serve as the new threads. |
