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Bleed air in aerospace engineering is compressed air taken from the compressor stage of a gas turbine, upstream of its fuel-burning sections.Automatic air supply and cabin pressure controller (ASCPC) valves bleed air from low or high stage engine compressor sections; low stage air is used during high power setting operation, and high stage air is used during descent and other low power setting ...
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.
While modern engines with advanced control units can avoid many causes of stall, jet aircraft pilots must continue to take this into account when dropping airspeed or increasing throttle. A compressor anti-stall system is a compressor bleed system that automatically dumps away unwanted air to prevent compressor stalling. [5]
The components above, except the shaft, are linked by a parameter common to all of them, the flow rate of gas passing through the engine which is the same for all components at the same time (as a basic statement this is an acceptable approximation which ignores the addition of fuel in the combustor and bleeding air from the compressor). [4]
The most common source of compressed air for pressurization is bleed air from the compressor stage of a gas turbine engine; from a low or intermediate stage or an additional high stage, the exact stage depending on engine type. By the time the cold outside air has reached the bleed air valves, it has been heated to around 200 °C (392 °F). The ...
Hot air is "bled" off one or more engines' compressor sections into tubes routed through wings, tail surfaces, and engine inlets. Spent air is exhausted through holes in the wings' undersides. A disadvantage of these systems is that supplying an adequate amount of bleed air can negatively affect engine performance.
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 J58 compressor solution was to bleed airflow from the 4th compressor stage at speeds above about Mach 2. [29] The bleed flow, 20% at Mach 3, was returned to the engine via 6 external tubes to cool the afterburner liner and primary nozzle as well as to provide extra air for combustion. [30]