gamma rays. A form of electromagnetic radiation that results from nuclear fission. Gamma rays have the ability to penetrate solid material, and they are used in the radiographic method of nondestructive inspection.
garnet paper. An abrasive and polishing paper made by coating one side of a sheet of flexible paper with a layer of crushed garnet.
gas. The physical state of matter in which a material takes the shape of its container and expands to fill the entire container. Oxygen and nitrogen are two chemical elements that are gases at normal room temperature and pressure. The air we breathe is a physical mixture of gases, primarily nitrogen and oxygen.
gas discharge tube (electron tube). A gas-filled diode electron tube used in a high energy capacitor-discharge ignition system for a turbine engine. The discharge tube blocks all electron flow until the voltage across its electrodes builds up to the ionization voltage of the gas inside the tube. When this voltage is reached, the gas ionizes and the tube conducts, discharging the capacitor through the high-voltage transformer.
gas-filled tube (electron tube). An electron tube whose envelope is filled with an inert gas, such as argon. The inert gas prevents the heated elements from oxidizing.
gas generator (gas turbine engine). The basic gas turbine engine consisting of the compressor, diffuser, combustor, and turbine. The gas generator, also called the core engine, is the part of a turbine engine that produces the hot, high-velocity gases. The gas generator does not include the inlet duct, fan section, free power turbines, or the tail pipe.
gasket. A seal between two stationary objects. A gasket is usually made of a soft material so it can conform to the surfaces of the two parts and form a leakproof seal. A gasket is similar to a packing, except a packing is used when there is relative motion between the parts being sealed.
gasoline. A liquid hydrocarbon fuel obtained from the distillation of crude oil. Gasoline is the most commonly used fuel for aircraft reciprocating engines and automobile engines.
gassing (battery condition). A condition that occurs near the end of the charging cycle of lead-acid storage batteries. Hydrogen and oxygen are released as free gases, hydrogen at the negative plate, and oxygen at the positive plate.
gas tungsten arc welding. See GTAW.
gas turbine engine. An internal combustion engine in which energy is released from the fuel in a constant-pressure cycle. Air is taken into the engine and compressed by either an axial-flow or a centrifugal compressor. The compressed air then passes into the combustion chambers where fuel is sprayed into a continuously burning fire. The burning fuel heats and expands the air which then flows through a turbine, where some of the energy is extracted to turn the compressor. The energy remaining in the gases leaving the engine causes the exhaust velocity to be greater than that of the air entering the engine, and this acceleration produces thrust.
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