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General Electric TF39 / CTF39


A TF39 on a C-5 Galaxy


The General Electric TF39 is a high-bypass turbofan engine. Developed to power the Lockheed C-5 Galaxy and first run in 1964, 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.

The TF39 is 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 is snubbered ('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 to the fan rotor which has a set of inlet guide vanes for the outer bypass section and the core booster stage located in front of the fan rotor, rather than behind. This unique design is clearly seen from the front.

The only application was the Lockheed C-5A/B/C Galaxy.



Type: Turbofan
Length: 312 in (792 cm)
Diameter: 97 in (246 cm)
Dry weight: 8000 lb (3630 kg)
Compressor: Axial, 1 stage fan, 5 stage low pressure compressor, 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
Specific fuel consumption: 0.313 lb/lbf-hr
Thrust-to-weight ratio: 5.4:1



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