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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.
In November 2016, Pratt had fixed the issue of engine start time and wanted to deliver 150 powerplants by the year-end, 50 fewer than originally planned. This was because of low yield of fan blades when less than one-third were passing inspection at the start of the year compared to 75% success for the latest. 350–400 engine deliveries were ...
Single-engine light aircraft fuel tanks are usually in the wings, but some aircraft have a small "header tank" between the normal fuel tank and the engine, to facilitate reliable fuel flow to the engine. On many small or very old single-engine header tanks (and even main tanks) are often mounted above and/or immediately behind the engine.
Some engine maintenance manuals refer to such systems as "customer bleed air". [3] [4] [5] Bleed air is valuable in an aircraft for two properties: high temperature and high pressure (typical values are 200–250 °C (400–500 °F) and 275 kPa (40 psi), for regulated bleed air exiting the engine pylon for use throughout the aircraft).
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.
The type of jet engine used to explain the conversion of fuel into thrust is the ramjet.It is simpler than the turbojet which is, in turn, simpler than the turbofan.It is valid to use the ramjet example because the ramjet, turbojet and turbofan core all use the same principle to produce thrust which is to accelerate the air passing through them.