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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The clock spring or weights add a tiny bit of energy to the pendulum each time it swings, and by adding as much energy as the pendulum loses because of friction, the pendulum can be kept swinging. pendulum valves (pneumatic gyro horizon component). Gravity-operated air valves mounted on the bottom of the gyro housing in a gyro horizon instrument. Air used to spin the gyro leaves the housing through these valves. If the gyro should tilt, the size of the holes covered by the valves changes, and the exhausting air produces a force that causes the gyro to erect. penetrant dwell time. The length of time a part is left in the penetrant when preparing it for inspection by the fluorescent or dye penetrant method. The hotter the part and the longer the penetrant dwell time, the smaller the fault that will be detected. penguin trainer (early training aircraft). A type of training aircraft used by the French in the early stages of World War I. The engines in these aircraft were not powerful enough to produce flight, but the student was able to develop enough feel of the controls to allow an effective transition to a flyable aircraft. pentagrid converter (electron tube). A mixer tube used in a superheterodyne radio receiver. A pentagrid converter tube has five grids, a cathode, a plate, and a filament. The incoming radio-frequency signal is applied to the signal grid, and a signal from a local oscillator is applied to the oscillator grid. The two signals mix and form two additional signals. The frequency of one is the sum of the two, and the frequency of the other is the difference between the two. The other three grids in the pentagrid tube are: two screen grids and one suppressor grid. pentavalent element. A chemical element with five electrons in its valence shell. Nitrogen, arsenic, antimony, and bismuth are pentavalent elements. pentode (electron tube). A vacuum tube with five active electrodes. A pentode tube has a cathode, a control grid, a screen grid, a suppressor grid, and a plate, or anode. percussive welding. A method of electric arc welding, used to attach studs to metal plates. A large amount of electrical energy is stored in capacitors and released through the stud. This produces a high current density between the stud and the plate. The high current density ionizes the air and allows an arc to form between the stud and the plate. The arc melts the end of the stud and the area of the surface of the plate where the stud is to be attached. The stud is pressed into the molten metal to complete the weld. perfect dielectric. A dielectric (insulator) that, when an electric field is removed, returns to the circuit all the energy used to establish the field. A perfect dielectric has absolutely no conductivity — its resistance is infinite. The only known perfect dielectric is a vacuum. perforate. To punch a series of holes in a material. Paper is often perforated with a series of tiny holes in a straight line, so it will tear evenly along the perforations. |
