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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ground fog (meteorology). A fog that conceals less than six tenths of the sky and is not a part of the cloud base. ground idle (gas turbine engine operating specification). The engine speed normally used for operating a gas turbine engine on the ground so it produces the minimum amount of thrust. Ground idle is normally in the range of 60% to 70% of the maximum RPM. ground loop (aircraft operation). A sharp, uncontrolled change in direction of an airplane on the ground. Tail wheel-type airplanes are highly subject to ground looping because their center of gravity is behind the point at which the main wheels contact the ground. ground loop (electrical condition). A condition of unwanted current flow in a circuit that uses shielded wire (wire encased in a braided metal cover). The purpose of the shielding is to intercept and carry to ground electrical energy radiated from the wires inside the shielding. If the shielding is connected to the ground at more than one point, it is possible for current to flow out one connection, through the ground, and back into the shielding through another connection. This current flowing in the shielding can interfere with delicate electrical signals in the shielded wire. To prevent ground loops, the shielding is grounded at one point only. ground plane (radio antenna component). A reflector used with a vertically polarized, quarter-wavelength radio antenna. Horizontal arms or a flat metal plane that sticks out at least a quarter wavelength from the base of the antenna reflects the signal. ground potential (electrical circuit condition). An electrical condition in which there is no voltage difference, or potential, between a point at ground potential and the ground point in the circuit. ground power unit. See GPU. ground resonance (helicopter operation). Destructive vibration that occurs with a helicopter, usually on landing. If the helicopter touches down rough and unevenly, the shock can throw a load into the lead-lag hinges of the rotor blades and cause the blades to oscillate (move back and forth) about this hinge. If the frequency of this oscillation is the same as the resonant frequency of the fuselage, the energy will cause the helicopter to strike the ground hard with the opposite skid or wheel. This will increase the energy and cause more severe contact with the ground. If corrective action is not taken immediately, either lifting the helicopter or placing it firmly on the ground, ground resonance can destroy it. ground-return circuit (electrical circuit). An electrical circuit using the ground or the structure of a vehicle as one of its conductors. Almost all automobiles and aircraft use ground-return electrical systems. One of the terminals of the battery, usually the negative terminal, is connected directly to the framework of the vehicle. One wire is used to connect the components to the positive terminal of the battery, and another wire connects the component to the structure. The return current from the component flows back to the battery through the structure. |
