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These motors can weigh up to 75% less than an equivalent electrical system. [15] The compressed air can be supplied from an on-board auxiliary power unit (APU), a portable gas generator used by ground crew or by cross feeding bleed air from a running engine in the case of multi-engined aircraft. [19]
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]
The first German jet engines built during the Second World War used a mechanical APU starting system designed by the German engineer Norbert Riedel.It consisted of a 10 horsepower (7.5 kW) two-stroke flat engine, which for the Junkers Jumo 004 design was hidden in the engine nose cone, essentially functioning as a pioneering example of an auxiliary power unit for starting a jet engine.
Air bled from the engine fan is blown across the pre-cooler, located in the engine strut, and absorbs excess heat from the service bleed air. A fan air modulating valve (FAMV) varies the cooling airflow to control the final air temperature of the service bleed air. Notably, the Boeing 787 does not use bleed air to pressurize the cabin.
Low pressure (40–70 psi or 280–480 kPa), high volume air from the compressor section of the APU is bled off through a system of pipes to the engines where it is directed into the starting system. This bleed air is directed into a mechanism to start the engine turning and begin pulling in air. The starter is usually an air turbine type ...
The Mitsubishi LE-5A was the world's first expander bleed cycle engine to be put into operational service. [5] The Mitsubishi LE-9 is the world's first first stage expander bleed cycle engine. [6] Blue Origin chose the expander bleed cycle for the BE-3U engine used on the upper stage of its New Glenn launch vehicle. [7]
This valve serves several functions. The first function is to act as a fuel shut-off valve. This is required to provide the crew with a means to prevent fuel reaching the engine in case of an engine fire. The second function is to allow the pilot to choose which tank feeds the engine. Many aircraft have the left tank and right tank selections ...
The Pratt & Whitney JT8D is a low-bypass (0.96 to 1) turbofan engine introduced by Pratt & Whitney in February 1963 with the inaugural flight of the Boeing 727.It was a modification of the Pratt & Whitney J52 turbojet engine which powered the US Navy A-6 Intruder and A-4 Skyhawk attack aircraft.