General Electric CF6

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CF6 turbofan at the KLM engine shop
CF6 turbofan at the KLM engine shop

The General Electric TF39 and CF6 are a family of high-bypass turbofan engines. Originally developed as the TF39 to power the C-5 Galaxy, they were the first high-power high-bypass jet engines available, and went on to power a wide variety of civilian airliners. Their primary competition is the Rolls-Royce RB211, and derivatives of both engine designs power almost every widebody airliner currently flying. The basic engine core also forms the basis for the LM2500, LM5000 and LM6000 marine and power generation turboshafts. GE-Aviation intends to replace the CF6 family with the GEnx, which are expected to enter service in 2008.

Contents

[edit] History

GE CF6 high-bypass turbofan
GE CF6 high-bypass turbofan

The United States Air Force opened the "CX-X Program" in 1964, intending to produce a next-generation strategic airlifter. Of the several airframe and engine proposals returned for consideration, in 1965 Lockheed's aircraft design and General Electric's engine design were selected for the new design.

The high-bypass turbofan was a huge leap in engine performance, offering high thrust of 43,000 pounds, while improving fuel efficiency by about 25%.[1] The TF39 had an 8-to-1 bypass ratio, 25-to-1 compressor pressure ratio, a 2,500 °F (1,370 °C) turbine temperature made possible by advanced forced-air cooling. The first engine went for testing in 1965. Between 1968 and 1971, 463 TF39-1 and -1A engines were produced and delivered to power the C-5A fleet.

The engine was then offered for civilian use as the CF6, and quickly found interest in two designs being offered for a recent Eastern Airlines contract, the Lockheed L-1011 and McDonnell Douglas DC-10. Although the L-1011 would eventually select the RB211, thus creating the CF6's greatest competitor, the DC-10 stuck with the CF6 and made it a success in this market as well when it started flying in 1971. It was also selected for versions of the Boeing 747, which was a development of Boeing's unsuccessful entry for the CX-X. Since then the CF6 has powered versions of the Airbus A300, 310 and 330, Boeing 767, and McDonnell Douglas MD-11.[2]

[edit] Variants

[edit] TF39

The TF39 is a revolutionary 1960s engine rated from 41,000 to 43,000 lbf (191 to 205 kN) of thrust. It employed a great deal of then-new technological features such as:

  • 1½ stage fan blades (unique to TF39).
  • 8:1 bypass ratio.
  • Variable stator vanes.
  • Turbines equipped with advanced cooling.
  • Fuel efficiency better than any engines available at the time.
  • Cascade-type thrust reversers.

Mechanically, the TF39 is rather unusual for a high bypass ratio turbofan; the single stage snubbered[a] fan rotor has a set of inlet guide vanes for the outer bypass section and the core booster stage is located in front of the fan rotor, rather than behind. The following sectional view shows the fan arrangement of the TF39 (http://www.aircraftenginedesign.com/pictures/TF39.gif). Note the very long gas generator used in this pioneering design.

[edit] CF6-6

An FAA cutaway diagram of the CF6-6 engine
An FAA cutaway diagram of the CF6-6 engine

The CF6-6 was a development of the military TF39. It was first utilized on the McDonnell Douglas DC-10-10.

This initial version of the CF6 comprises a single stage fan, with one core booster stage, driven by a 5-stage LP (low pressure) turbine, supercharging a 16-stage HP (high pressure) axial compressor driven by a 2-stage HP turbine; the combustor is annular and exhaust separate jets. The 86.4 in (2.19 m) diameter fan generates an airflow of 1300 lb/s (590 kg/s), resulting in a relatively high bypass ratio of 5.72. The overall pressure ratio of the compression system is 24.3. At maximum take-off weight, the engine develops a static thrust of 40,000 lbf (178 kN).

A complete disintegration of a CF6-6 fan assembly resulted in the loss of cabin pressurization of National Airlines Flight 27 over New Mexico, USA in 1973.[3] The failure of a CF6-6 resulted in the Sioux City, Iowa USA crash of United Airlines Flight 232 in 1989.

[edit] CF6-50

The CF6-50 series are high-bypass turbofan engines rated between 46,000 and 54,000 lbf (205 to 240 kN) of thrust. The CF6-50 was developed into the LM2500 industrial and marine turboshaft engines. It was launched in 1969 to power the long range McDonnell Douglas DC-10-30, and was derived from the earlier CF6-6.

Because a significant increase in thrust and therefore core power was required not long after the -6 had entered service, General Electric could not increase (HP) turbine rotor inlet temperature significantly, so they took the very expensive decision to reconfigure the CF6 core to increase its basic size. They achieved this by removing two stages from the rear of the HP compressor (even leaving an empty air passage, where the blades and vanes had once been located). two extra booster stages were added to the IP (intermediate pressure) compressor, which increased the overall pressure ratio to 29.3. Although the 86.4 in (2.19 m) diameter fan was retained, the airflow was raised to 1450 lb/s (660 kg/s), yielding a static thrust of 51,000 lbf (227 kN). The increase in core size and overall pressure ratio, significantly raised the core flow, resulting in a decrease in bypass ratio to 4.26.

In late 1969, the CF6-50 was selected to power the then new Airbus A300. Air France became the launch customer for the A300 by ordering six aircraft in 1971. In 1975, KLM was the first airline to order the Boeing 747 powered by the CF6-50. This led further developments to the CF6 family such as the CF6-80.

[edit] CF6-80

The CF6-80 series are high-bypass turbofan engines with a thrust range of 48,000 to 75,000 lbf (214 to 334 kN). It is an advanced development of the earlier successful CF6-50 series engine, but despite superficial resemblance, it is a completely new engine with no interchangeable parts. Although the HP compressor still has 14 stages, GE did take the opportunity to tidy-up the design, by removing the empty air passage at compressor exit.

Following a series of high-pressure turbine failures,[4] [5] [6] some which resulted in 767s being written off,[7] [8] [9] the FAA has issued an airworthiness directive mandating inspections for over 600 engines. The NTSB feels this number should be increased to include all -80 series engines with more than 3000 cycles since new or since last inspection. [10]

The -80 series is divided into three distinct models.

[edit] CF6-80A

The CF6-80A, which has a thrust rating of 48,000 to 50,000 lbf (214 to 222 kN), powered two twinjets, the Boeing 767 and Airbus A310. The GE-powered 767 entered airline service in 1982, and the GE powered A310 in early 1983. It is rated for ETOPS operations.

For the CF6-80A/A1, the fan diameter remains at 86.4 in (2.19 m), with an airflow of 1435 lb/s (651 kg/s). Overall pressure ratio is 28.0, with a bypass ratio of 4.66. Static thrust is 48,000 lbf (214 kN). The basic mechanical configuration is the same as the -50 series.

[edit] CF6-80C2
A Delta Air Lines Boeing 767-400ER with CF6-80C2 engines
A Delta Air Lines Boeing 767-400ER with CF6-80C2 engines

The CF6-80C2, which entered revenue service in October 1985, has a thrust rating of 52,500 to 63,500 lbf (234 to 282 kN). It has a reputation of good fuel economy in its thrust class. The CF6-80C2 is certified with 16 different thrust ratings. This versatile engine has the most widespread use of any large turbofan engine.[citation needed]

For the CF6-80C2-A1, the fan diameter is increased to 93 in (2.36 m), with an airflow of 1750 lb/s (790 kg/s). Overall pressure ratio is 30.4, with a bypass ratio of 5.15. Static thrust is 59,000 lbf (263 kN). An extra stage is added to the HP compressor, and a 5th to the LP turbine.

The CF6-80C2 is currently certified on eleven wide-body aircraft models including the Boeing 747 and McDonnell Douglas MD-11. The CF6-80C2 is also certified for ETOPS-180 for the A300, A310, Boeing 767 aircraft and the U.S. Air Force's C-5M Super Galaxy.

[edit] CF6-80E1

The CF6-80E1 is specifically designed for the Airbus A330, with thrust rating of 67,500 to 72,000 lbf (300 to 334 kN). For the CF6-80E1A2, the fan diameter is increased to 96 in (2.44 m), with an airflow of 873,6 kg/s 1925 lb/s (875 kg/s). Overall pressure ratio is 32.6, with a bypass ratio of 5.3.

[edit] Other variants

The industrial and marine development of the CF6-80C2, the LM6000 Series, has found wide use including fast ferry and high speed cargo ship applications, as well as in power generation. Unlike the LM2500 and LM5000, it is capable of cold (compressor) end drive allowing for an axial exhaust which aids power output and efficiency. The LM6000 actually uses the LP compressor section from the CF6-50.

[edit] CF6-32

The CF6-32 was intended to be a stripped-down version of the CF6-80 for the Boeing 757. It was never launched due to lack of interest from airlines.

[edit] Applications

[edit] References

  1. ^ General Electric - CF6 history
  2. ^ General Electric - Model TF39
  3. ^ Applying Lessons Learned - National Airlines Flight 27 Federal Aviation Administration
  4. ^ Report on aircraft C-FTCA 6 September 1997 engine failure Aviation Safety Network
  5. ^ Report on aircraft PP-VNN 7 June 2000 engine failure Aviation Safety Network
  6. ^ Report on aircraft ZK-NBC 8 December 2002 engine failure Aviation Safety Network
  7. ^ Report on aircraft N654US 22 September 2000 engine failure Aviation Safety Network
  8. ^ Report on aircraft N330AA 2 June 2006 engine failure Aviation Safety Network
  9. ^ N330AA photos airliners.net
  10. ^ NTSB wants at-risk GE CF6 engines removed Flight International, September 5 2006

[edit] Notes

a.^  Snubbers are protuberances that stick-out at right angles to the fan aerofoil, somewhere between mid-span and blade tip. The snubbers on adjacent fan blades butt-up against each other, in a peripheral sense, and improve the vibration characteristics of the blade.

[edit] External links

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