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Cutaway view of an air-start motor of a General Electric J79 turbojet. With air-start systems, gas turbine engine compressor spools are rotated by the action of a large volume of compressed air acting directly on the compressor blades or driving the engine through a small, geared turbine motor. These motors can weigh up to 75% less than an ...
The compressed air is heated in the combustor and passes through the turbine, then expands in the nozzle to produce a high speed propelling jet [3] Turbojets have a low propulsive efficiency below about Mach 2 [ citation needed ] and produce a lot of jet noise, both a result of the very high velocity of the exhaust.
The increased thrust from the C-D nozzle (2,000 lb, 910 kg at sea-level take-off) on this engine raised the speed from Mach 1.6 to almost 2.0 enabling the Air Force to set a world's speed record of 1,207.6 mph (1,943.4 km/h) which was just below Mach 2 for the temperature on that day. The true worth of the C-D nozzle was not realised on the F ...
The propelling nozzle converts a gas turbine or gas generator into a jet engine. Power available in the gas turbine exhaust is converted into a high speed propelling jet by the nozzle. The power is defined by typical gauge pressure and temperature values for a turbojet of 20 psi (140 kPa) and 1,000 °F (538 °C). [18]
The engine was first introduced as a technology demonstrator in 1977. [3] The PW100 was first tested in March 1981, made its initial flight in February 1982 on a Vickers Viscount testbed aircraft, [4] and then entered service in December 1984 on a Dash 8 regional aircraft for NorOntair.
After M e = 1 is reached at the nozzle exit for p r = 0.5283p 0, the condition of choked flow occurs and the velocity throughout the nozzle cannot change with further decreases in p r. This is due to the fact that pressure changes downstream of the exit cannot travel upstream to cause changes in the flow conditions.
The SS.12/AS.12 was basically a scaled-up version of the SS.11/AS.11, with a massive increase in range and warhead weight. The SS.12/AS.12 original mission was primarily to be anti-shipping from naval helicopters and combat aircraft or ground launchers, and secondarily for use against heavy field fortifications.
A direct start system as used on a marine slow-speed diesel is required to have up to 12 starts on a non-reversing engine or 6 starts on a reversible, or geared, engine. When starting the engine, compressed air is admitted to whichever cylinder has a piston just over top dead center , forcing it downward. [ 2 ]