Bleed air in gas turbine engines is compressed air taken from within the engine, after the compressor stage(s) and before the fuel is injected in the burners. This compressed air can be used in many different ways, from de-icing to pressurising the cabin to pneumatic actuators. However, bleed air is quite hot and if being used in the cabin or other low temperature areas it must be cooled, even refrigerated. Bleed air is valuable in an aircraft for two properties: its high temperature and its high pressure. A Pratt and Whitney turbofan engine for the F-15 Eagle is tested at Robins Air Force Base, Georgia, USA. The tunnel behind the engine muffles noise and allows exhaust to escape. ... In thermodynamics, temperature is the physical property of a system that underlies the common notions of hot and cold —something that is hotter has the greater temperature. ... Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface. ...

Newer aircraft rely more on electricity, reducing the need for compressed air. Since most gas turbine engines use multiple compressor stages, some newer engines have the bleed air inlet between compressor stages to reduce the temperature of the compressed air.

Merits of bleed air

In civil aircraft, its primary use is to provide pressure for the aircraft cabin by supplying air to the Environmental Control System. Additionally, bleed air is used to keep critical parts of the aircraft (such as the wing leading edges) ice-free. A cabin or cab is an enclosed space, in a ship, see cabin (ship), in an aircraft or spacecraft as a log cabin as in a hansom cab see also Uncle Toms Cabin This is a disambiguation page — a navigational aid which lists other pages that might otherwise share... The Environmental Control System of an airplane provides air supply, thermal control and pressurization for the passengers and crew. ... A Laughing Gull on the beach in Atlantic City. ... 1970 Model American Aviation AA-1 Yankee showing the wings straight leading edge The Leading edge is that part of the wing that, when it is in motion, first contacts the air. ...

When used for cabin pressurization, the air from the engine must first be cooled (as it exits the compressor stage at temperatures as high as 300 °C) by passing the bleed air through an air-to-air heat exchanger cooled by cold outside air. It is then fed to an air conditioning unit which regulates the temperature and flow of air into the cabin, keeping the environment comfortable. A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. ... Note: in the broadest sense, air conditioning can refer to any form of heating, ventilation, and air-conditioning. ...

A similar system is used for wing de-icing. In icing conditions, water droplets condensing on a wing's leading edge can freeze at the ambient temperatures experienced during flight. This build-up of ice adds weight and changes the shape of the wing, causing a degradation in performance, and possibly a fatal loss of lift. To prevent this, warm bleed air is pumped through the inside of the wing's leading edge. This heats up the metal, preventing the formation of ice. Alternatively, the bleed air may be used to inflate a rubber boot glued to the leading edge, breaking the ice loose. Deicing is the process of removing ice from a surface. ... Condensation is the change in matter1 of a substance to a denser phase, such as a puppy gas (or vapor) to a liquid. ... The acronym ICE can refer to: InterCity Express, a German high-speed train InterCity Express (CityTrain), an interurban train used by QR CityTrain in South East Queensland, Australia Internal combustion engine, a fuel engine In-circuit emulator, a computer hardware device In case of emergency, emergency number in mobile phones... Lift consists of the sum of all the fluid dynamic forces on a body perpendicular to the direction of the external flow approaching that body. ...

Recent developments in civil aircraft

Bleed air systems have been in use for several decades in passenger jets. Recently, Boeing announced that its new aircraft, the 787 would operate without use of bleed air (and the two engines proposed for the aircraft, the General Electric GEnx and the Rolls-Royce Trent 1000, are designed with this in mind). This represents a departure from traditional winged aircraft design, and proponents state that eliminating bleed air improves engine efficiency, as there is no loss of mass airflow and therefore energy from the engine, leading to lower fuel consumption. Additionally, eliminating bleed air may reduce the aircraft's mass by removing a whole series of pumps, heat exchangers and other heavy equipment. Lastly, advocates of the design say it improves safety as heated air is confined to the engine core, as opposed to being pumped through pipes and heat exchangers in the wing and near the cabin, where a leak could damage surrounding systems. Boeing Commercial Airplanes (BCA), based in Renton Washington, is a unit of The Boeing Company, consisting of the Seattle-based former Boeing Airplane Company (the civil airliner division), as well as the Long Beach-based Douglas Aircraft division of the former McDonnell Douglas Corporation. ... An Air France Boeing 777, a modern passenger jet. ... The Boeing 787 Dreamliner is a mid-sized wide body passenger airliner currently under development by Boeing Commercial Airplanes and scheduled to enter service in 2008. ... General Electric Aircraft Engines (GEAE) is the top supplier of aircraft engines in the world and offers engines for the majority of commercial aircraft. ... Boeing 787 The General Electric GEnx (General Electric Next-generation) is an advanced turbofan under development by GE Aircraft Engines (GEAE) for the Boeing 787. ... Rolls-Royce plc is the second-largest aircraft engine maker in the world, behind General Electric Aviation. ... Rolls-Royce Trent 900 on A380 prototype Rolls Royce Trent is a family of high-bypass turbofan engines manufactured by Rolls-Royce. ...

Skeptics point out that by eliminating bleed air there is then a requirement to find alternative methods of providing cabin heating, de-icing and other functions previously covered by bleed air, which require additional systems which take up space, weight, and electrical energy. Therefore this approach is less efficient from an overall point of view (taking the entire aircraft into consideration and not just the engines), as it involves drawing in very cold ambient air and heating it, a very energy-intensive process.

Airbus does not currently (as of November 2004) have any plans to eliminate bleed air from its 787 competitor, the A350, while Boeing is actively pursuing this technology, touting it as one of the main advantages of its design. Airbus S.A.S., based in Toulouse, France, is a leading aircraft manufacturer. ... Airbus A350 XWB concept “A350” redirects here. ...

There has been claims by Dagbladet [1] and The Observer [2] that hazardous cabin gases can be caused by leakage of toxic gases produced by modern synthetic engine oils under high temperatures in the gas turbines, which subsequently gets distributed through the bleed air. Dagbladet is Norways third largest newspaper with a circulation of 191,164 copies in 2002. ... Wikipedia does not yet have an article with this exact name. ... Hazard may mean: Dangers, risks, problems A hazard is a source of potential harm. ... Cabin pressurization is the active pumping of air into the cabin of an aircraft to increase the air pressure within the cabin. ... Toxic redirects here, but this is also the name of a song by Britney Spears; see Toxic (song) Look up toxic and toxicity in Wiktionary, the free dictionary. ... Synthetic oil is oil consisting of chemical compounds which were not originally present in crude oil (petroleum) but were artificially made (synthesized) from other compounds. ... This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings. ...

A non profit group called AOPIS [3] was set up by crew members in 2001 to tackle the health and flight safety issues of bleed air being contaminated by synthetic jet engine oils and hydraulic fluids.