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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).
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 ...
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.
The Pratt & Whitney J58 (company designation JT11D-20) is an American jet engine that powered the Lockheed A-12, and subsequently the YF-12 and the SR-71 aircraft. It was an afterburning turbojet engine with a unique compressor bleed to the afterburner that gave increased thrust at high speeds.
Bleed air from the engines, an auxiliary power unit, or a ground source, which can be in excess of 150 °C and at a pressure of perhaps 32 psi (220 kPa), [1] is directed into a primary heat exchanger. Outside air at ambient temperature and pressure is used as the coolant in this air-to-air heat exchanger.
An interesting feature of all three German jet engine designs that saw production of any kind before May 1945: the German BMW 003, Junkers Jumo 004 and Heinkel HeS 011 axial-flow turbojet engine designs was the starter system, which consisted of a Riedel 10 hp (7.5 kW) flat twin two-stroke air-cooled engine hidden in the intake, and essentially ...
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By the time the cold outside air has reached the bleed air valves, it has been heated to around 200 °C (392 °F). The control and selection of high or low bleed sources is fully automatic and is governed by the needs of various pneumatic systems at various stages of flight. Piston-engine aircraft require an additional compressor, see diagram ...