General Electric TF39

Development

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, Lockheed's aircraft and General Electric's engine were selected for the new design in 1965.

The high-bypass ratio of 8:1 for the TF-39 had its origins in the lift-fan technology demonstrated by GE in the XV-5 Vertifan aircraft. lift-fan driven by a gas generator (J85). The bpr in VTOL operation was 12.3. This tip-turbine driven lift-fan concept was turned 90 degrees and developed as an 80-inch-diameter "cruise fan" demonstrator, driven by a J79 gas generator. This was developed into the TF39 with a 97 in diameter fan.

The high-bypass substantially improved the thrust and fuel consumption compared to the previous GE jetliner turbofan, the CJ805-21. It had two and a half times the thrust, while improving fuel efficiency by about 25%. 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 TF39 core was used for the CF6 series of engines, and the LM2500 and LM6000 marine and industrial gas turbines.

Design

The TF39 produced 41,000 to 43,000 lb (191 to 205 kN) of thrust. It had an 8:1 bypass ratio, a 25:1 compressor pressure ratio, and a 2,500 °F (1,370 °C) turbine temperature made possible by the latest cooling technology.

The engine included features developed from previous GE engines:

• Variable stator vanes (used in the J79/CJ805)
• Turbine cooling techniques (more advanced than used on the YJ93)
• Cascade-type thrust reverser (from the CJ805)
• Snubbered first stage fan blades (snubbers, or mid-span shrouds, had been introduced by GE on the YJ93 first stage compressor blades)

By modern standards the Low Pressure Compressor on the TF-39 is fairly unique as a single T-stage is mounted upstream of the fan rotor, rather than behind it. Although this T-stage supercharges the inner section of the fan rotor, not all of this airstream enters the High Pressure Compressor as a fair proportion also enters the bypass duct to supplement the air discharging from the outer section of the fan. In other words there are three streams leaving the fan, two of which enter the bypass duct.

Operational history

On September 7, 2017, the last C-5A powered with TF39 engines made its final flight to Davis-Monthan Air Force Base for retirement. The only application for the TF39, the Galaxy military transport, was re-engined with the more modern F138-GE-102, a military version of the General Electric CF6-80C2. Re-engining for the whole fleet took place from 2008 to 2018.

Applications

• Lockheed C-5A/B/C Galaxy

Specifications (TF39-1C)

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References

References

1. This aircraft had two X353-5 engines, each consisting of a 62.5-inch-diameter"Aerodynamic characteristics of a Large-Scale Model with a High Disk Loading Lift Fan Mounted in the Fuselage" Aoyagi, Hickey and deSavigny, NASA TN D-775
2. "Jet Propulsion for Aerospace Applications" Second Edition, Hesse and Mumford, Pitman Publishing Corporation, 1964, Table 11.1
3. "seven decades of progress" General Electric, {{ISBN. 0-8168-8355-6, Aero Publishers Inc. p.152
4. [http://geae.com/engines/commercial/cf6/history.html General Electric - CF6 history] {{webarchive. link. (2009-01-27)
5. "Gas Turbine Technology Evolution: A Designer's Perspective" Bernard L. Koff, Journal of Propulsion and Power, Vol.20 No. 4, July–August 2004, p.591
6. https://aviation.stackexchange.com/questions/51747/why-does-the-cf6-have-a-lower-bypass-ratio-than-the-tf39
7. Smith, Hanna. (8 September 2017). "And then there were none, the final C-5A departs Westover ARB for retirement > Westover Air Reserve Base > Article Display".
8. (12 April 2016). "An era of Dover-built TF39 engines throttles down".
9. Gas Turbine Engines. ''Aviation Week & Space Technology Source Book 2009''. p. 119