The geared turbofan is a type of

turbofan The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the ''turbo'' portion refers to a gas turbine engine which ac ...

aircraft engine, with a

gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...

between the fan and the low pressure shaft to spin each at optimum angular velocities.

Technology

In a conventional turbofan, a single shaft (the "low-pressure" or LP shaft) connects the fan, the low-pressure compressor and the low-pressure turbine (a second concentric shaft connects the high-pressure compressor and high-pressure turbine). In this configuration, the maximum tip speed for the larger radius fan limits the rotational speed for the LP shaft and thus the LP compressor and turbine. At high bypass ratios (and thus high radius ratios) the tip speeds of the LP turbine and LP compressor must be relatively low, which means extra compressor and turbine stages are required to keep the average stage loadings and, therefore, overall component efficiencies to an acceptable level. In a geared turbofan, a planetary reduction gearbox between the fan and the LP shaft allows the latter to run at a higher rotational speed thus enabling fewer stages to be used in both the LP turbine and the LP compressor, increasing efficiency and reducing weight. However, some energy will be lost as heat in the gear mechanism and weight saved on turbine and compressor stages is partly offset by that of the gearbox. There are manufacturing cost and reliability implications as well. The lower fan speed allows higher bypass ratios, leading to reduced fuel consumption and much reduced noise. The

BAe 146 The British Aerospace 146 (also BAe 146) is a short-haul and regional airliner that was manufactured in the United Kingdom by British Aerospace, later part of BAE Systems. Production ran from 1983 until 2001. Manufacture by Avro International ...

is fitted with geared turbofans and is still one of the quietest commercial aircraft. A large part of the noise reduction is due to reduced fan tip speeds. In conventional turbofans the fan tips exceed the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...

causing a characteristic drone, requiring sound deadening. Geared turbofans operate the fan at sufficiently low rotational speed to avoid supersonic tip speeds.

History

After considering a geared design, General Electric decided against it for its

CFM LEAP The CFM International LEAP ("Leading Edge Aviation Propulsion") is a high-bypass turbofan engine produced by CFM International, a 50–50 joint venture between American GE Aviation and French Safran Aircraft Engines (formerly Snecma). It is th ...

due to weight and reliability concerns, postponing its use for a future application, after Pratt & Whitney began development of the geared

PW1000G The Pratt & Whitney PW1000G, also called the Geared Turbofan (GTF), is a high-bypass geared turbofan engine family produced by Pratt & Whitney. After many demonstrators, the program was launched with the Mitsubishi MRJ's PW1200G in March 2008, ...

Engines

Garrett TFE731 The Garrett TFE731 (now Honeywell TFE731) is a family of geared turbofan engines commonly used on business jet aircraft. Garrett AiResearch originally designed and built the engine, which due to mergers was later produced by AlliedSignal and no ...

Lycoming ALF 502 The Lycoming ALF 502/LF 507 (now:Honeywell ALF 502/LF 507) is a geared turbofan engine produced by Lycoming Engines, AlliedSignal, and then Honeywell Aerospace. Development In mid-1970, Avco Lycoming was advertising two Lycoming T55-derived ...

LF 507 The Lycoming ALF 502/LF 507 (now:Honeywell ALF 502/LF 507) is a geared turbofan engine produced by Lycoming Engines, AlliedSignal, and then Honeywell Aerospace. Development In mid-1970, Avco Lycoming was advertising two Lycoming T55-derived ...

Pratt & Whitney PW1000G The Pratt & Whitney PW1000G, also called the Geared Turbofan (GTF), is a high-bypass geared turbofan engine family produced by Pratt & Whitney. After many demonstrators, the program was launched with the Mitsubishi MRJ's PW1200G in March 2008 ...

* Rolls-Royce UltraFan *

Turbomeca Astafan The Turbomeca Astafan is a single-spool, variable-pitch turbofan engine developed from the Turbomeca Astazou. Despite successful flight-testing, an efficient, quiet and clean design (compared to turbojets and conventional turbofans) and some comme ...

Turbomeca Aspin The Turbomeca Aspin was a small French turbofan engine produced by Turbomeca in the early 1950s. This geared turbofan design was the first turbofan to fly, powering the Fouga CM.88 Gemeaux, Fouga Gemeaux test-bed aircraft on 2 January 1952.Gunsto ...

Tentatives

* Rolls-Royce/SNECMA M45SD, a derivative of

Rolls-Royce/SNECMA M45H The Rolls-Royce/SNECMA M45H is an Anglo-French medium bypass ratio turbofan produced specifically for the twin-engined VFW-Fokker 614 aircraft in the early 1970s. The design was started as a collaborative effort between Bristol Siddeley and ...

turbofan, designed to demonstrate ultra-quiet engine technologies, needed for STOL aircraft operating from city centre airports *

IAE SuperFan The IAE V2500SF SuperFan was a design study for a high-bypass geared turbofan derived from the IAE V2500. It was offered as the primary engine option for the Airbus A340 in January 1987. Although several customers signed preliminary contracts for ...

, an

IAE V2500 The IAE V2500 is a two-shaft high-bypass turbofan engine built by International Aero Engines (IAE) which powers the Airbus A320 family, the McDonnell Douglas MD-90, and the Embraer C-390 Millennium. The engine's name is a combination of the Roma ...

derivative proposed for the

Airbus A340 The Airbus A340 is a long-range, wide-body passenger airliner that was developed and produced by Airbus. In the mid-1970s, Airbus conceived several derivatives of the A300, its first airliner, and developed the A340 quadjet in parallel with ...

between 1987 and 1992 * Aviadvigatel PD-18R, a

derivative In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. F ...

of the gearless PD-14, based on its high-temperature core, to be completed by 2020

References

Notes

Bibliography

* * Francillon, René J. ''McDonnell Douglas Aircraft since 1920''. London: Putnam, 1979. . * {{refend Turbofan engines