General Electric TF39
|A TF39 on a C-5 Galaxy at ILA (Internationale LuftfahrtAusstellung) in Berlin, 2008|
|Major applications||Lockheed C-5 Galaxy|
|Variants||General Electric CF6|
|Developed into||General Electric LM2500|
The General Electric TF39 is a high-bypass turbofan engine. Developed to power the Lockheed C-5 Galaxy, it was the first high-power, high-bypass jet engine available. The TF39 was developed into the CF6 series of engines, and formed the basis of the General Electric LM2500 marine and industrial gas turbine.
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 turbofan was a huge leap in engine performance, offering a thrust of 43,000 pounds, while improving fuel efficiency by about 25%. 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.
- 1½ stage fan blades
- 8:1 bypass ratio
These features, together with advances in core technology below, contributed to a significant improvemment in fuel efficiency over any engines available at the time.
The engine also included features developed from previous GE engines
- Variable stator vanes (used in the J79/CJ805)
- Turbine cooling techniques (advanced from the J93 used in the XB-70)
- Cascade-type thrust reverser (from the CJ805)
- Snubbered first stage fan blades (snubbers (mid-span shrouds)introduced by GE on the YJ93 first stage compressor blades)
The fan was a unique, very complex design; the first stage extends to about half the second stage annulus and runs in a tip shroud. The blades are snubbered. 'Snubbers' are protuberances that stick-out at right angles to the fan aerofoil at mid to 2/3 span. At speed the snubbers on adjacent fan blades butt-up against each other to prevent blade failures due to flutter. This particular aspect of the design, together with the second stage inlet guide vanes in the outer half of the duct, is seen looking in the engine intake.
The fan second stage has a mid-span platform/flow splitter which separates the single-stage outer annulus from the 2-stage inner annulus. The inner portions of the first and second stage blades provide supercharging for the 16-stage compressor.
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. This aircraft had two X353-5 engines each consisting of a 62.5 in. diameter 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 80in. diameter "cruise fan" demonstrator, driven by a J79 gas generator. For the CX-X program GE demonstrated a half-scale engine, the GE1/6, with 15,830 lb thrust and an sfc of 0.336. This was developed into the TF39 with a 97 in. fan.
- Lockheed C-5A/B/C Galaxy
Data from 
- Type: Turbofan
- Length: 312 in (792 cm)
- Diameter: 97 in (246 cm)
- Dry weight: 8000 lb (3630 kg)
- Compressor: Axial, 2 stage fan, 16 stage high pressure compressor
- Combustors: Annular
- Turbine: Axial, 2 stage high pressure turbine, 6 stage low pressure turbine.
- Maximum thrust: 43,300 lbf (193 kN)
- Overall pressure ratio: 25:1
- Fuel consumption: ~3.7646 lb/s (1.7075 kg/s)
- Specific fuel consumption: 0.313 lb/lbf-hr
- Thrust-to-weight ratio: 5.4:1
- Related development
- Comparable engines
- Related lists
- General Electric - CF6 history
- "seven decades of progress" General Electric, ISBN 0-8168-8355-6, Aero Publishers Inc. p.152
- "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
- "Flight Manual USAF Series C5A and C5B Airplanes", TO 1C-5A-1, Lockheed Martin Corporation
- "Flutter and Resonant Vibration Characteristics of Engine Blades" A.V. Srinivasan, 97-GT-533, ASME, p.8
- www.planes.cz - TF39 front view
- www.airliners.net - TF39 running
- "Aviation Week" 16 August 1965, shown as Figure 35 in "The History Of The Rolls-Royce RB211 Turbofan Engine", ISBN 978-1-872922-48-5, The Rolls-Royce Heritage Trust
- "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
- "Jet Propulsion for Aerospace Applications" Second Edition,Hesse and Mumford,Pitman Publishing Corporation, 1964, Table 11.1
- "The Development of Jet and Turbine Engines", 4th edition, Bill Gunston, ISBN 0 7509 4477 3, p.192
- Gas Turbine Engines. Aviation Week & Space Technology Source Book 2009. p. 119
- Gunston, Bill (2006). World Encyclopedia of Aero Engines, 5th Edition. Phoenix Mill, Gloucestershire, England, UK: Sutton Publishing Limited. ISBN 0-7509-4479-X.
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