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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.
The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. [1] A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for every 1 kg of air passing through the core.
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, similar to the cartridge starter, but uses the APU's bleed air instead of the burning gases of the propellant cartridge. Most cart starters can also use APU air to turn them.
Early examples of different solutions to alleviate rotating stall in the front stages include the Rolls-Royce Avon with variable inlet guide vanes and interstage bleed, the General Electric J79 with variable inlet guide vanes and variable stators, the Bristol Olympus with split compressor and the Pratt & Whitney J57 with split compressor and intercompressor bleed.
The CFM56 is a high-bypass turbofan engine (most of the air accelerated by the fan bypasses the core of the engine and is exhausted out of the fan case) with several variants having bypass ratios ranging from 5:1 to 6:1, generating 18,500 to 34,000 lbf (80 kN to 150 kN) of thrust. The variants share a common design, and differ only in details.
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The Rolls-Royce Trent XWB is a high-bypass turbofan produced by Rolls-Royce Holdings.In July 2006, the Trent XWB was selected to exclusively power the Airbus A350. [2] The first engine was run on 14 June 2010, [3] it first flew on an A380 testbed on 18 February 2012, [4] was certified in early 2013, [5] and first flew on an A350 on 14 June 2013. [6]