ILA 2008 PD 083.JPG
A TF39 on a C-5 Galaxy at ILA (Internationale LuftfahrtAusstellung) in Berlin, 2008
Type High-bypass turbofan
National origin United States
Manufacturer GE Aviation
First run 1964
Major applications Lockheed C-5 Galaxy
Number built 463
Developed into General Electric CF6
General Electric LM2500

The General Electric TF39 was a high-bypass turbofan engine that was developed to power the Lockheed C-5 Galaxy. The TF39 was the first high-power, high-bypass jet engine developed. The TF39 was further developed into the CF6 series of engines, and formed the basis of the LM2500 and LM6000 marine and industrial gas turbine. On September 7, 2017, the last active C-5A powered with TF39 engines made its final flight to Davis-Monthan Air Force Base for retirement.[1][2] The TF39 was effectively retired, and all remaining active C-5 Galaxys are now powered by F138 (General Electric CF6-80C2) engines.


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%.[3] The TF39 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 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.


TF39s on a C-5 Galaxy, from the rear
TF39s on a C-5 Galaxy, from the rear
TF-39 on display at the Museum of Aviation
TF-39 on display at the Museum of Aviation

The TF39 was a revolutionary 1960s engine rated from 41,000 to 43,000 lbf (191 to 205 kN) of thrust. It introduced use of a large by-pass ratio which, together with advances in core technology, contributed to a significant improvement in fuel efficiency over engines available at the time.

The engine included features developed from previous GE engines:

Today, a conventional turbofan featuring a T-staged fan would have an overhung fan rotor (without any inlet guide vanes), followed by one or more T-stages supercharging the core stream alone.[6] The name T-staged fan is derived from the overall appearance of the LP compressor when the side elevation is shown diagrammatically.

GE took a different approach with their first high bypass ratio turbofan, the TF39. It is a unique, very complex design.[7] The T-stage, which supercharges the core stream, is located ahead of the main fan rotor. The T-stage itself comprises an overhung mini-rotor followed by a set of outlet guide vanes; the main fan rotor is located immediately behind these OGVs. Outboard of the T-stage rotor are the main inlet guide vanes, which only affect the bypass stream. The T-stage rotor extends to about half the main rotor stage annulus[5][8] and runs in a tip shroud. The main fan stage has a mid-span platform/flow splitter which separates the single-stage outer annulus from the two-stage inner annulus.[8] These two stages mainly supercharge the 16-stage high-pressure compressor.[9] However, a fair proportion of the air entering the T-stage is bled off into the bypass duct, there being two annular passages leading to the bypass duct. The nominal bypass ratio of 8:1 refers to the ratio of total bypass mass flow to HP compressor entry mass flow.

The rotor blades are snubbered. 'Snubbers' are protuberances that stick out at right angles to the fan aerofoil at mid[5] to 2/3 span.[10] At speed, the snubbers on adjacent fan blades butt-up against each other to prevent blade failures due to flutter.[10] They, together with the second-stage inlet guide vanes in the outer half of the duct, are visible when looking into the engine intake.[11][12]

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.[4] This aircraft had two X353-5 engines, each consisting of a 62.5-inch-diameter[13] lift-fan driven by a gas generator (J85). The bpr in VTOL operation was 12.3.[14] 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.[4] 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.[15] This was developed into the TF39 with a 97 in diameter fan.[8]


Specifications (TF39-1C)

A Boeing B-52E (Serial Number 57-0119) testing a TF39 on the right inboard engine pod. The TF39 has more than double the thrust of the twin Pratt & Whitney J57s that were originally in that spot.
A Boeing B-52E (Serial Number 57-0119) testing a TF39 on the right inboard engine pod. The TF39 has more than double the thrust of the twin Pratt & Whitney J57s that were originally in that spot.

Data from [16]

General characteristics



See also

Related development

Comparable engines

Related lists


  1. ^ 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".
  2. ^ Balik, Roland (12 April 2016). "An era of Dover-built TF39 engines throttles down". Air Mobility Command. Retrieved 9 February 2023.
  3. ^ General Electric - CF6 history Archived 2009-01-27 at the Wayback Machine
  4. ^ a b c d e "seven decades of progress" General Electric, ISBN 0-8168-8355-6, Aero Publishers Inc. p.152
  5. ^ a b c "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. ^ "br715 - Google Search".
  7. ^ " - Aviation Forums".
  8. ^ a b c "Flight Manual USAF Series C5A and C5B Airplanes", TO 1C-5A-1, Lockheed Martin Corporation
  9. ^ "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
  10. ^ a b "Flutter and Resonant Vibration Characteristics of Engine Blades" A.V. Srinivasan, 97-GT-533, ASME, p.8
  11. ^ TF39 front view.
  12. ^ TF39 running.
  13. ^ "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
  14. ^ "Jet Propulsion for Aerospace Applications" Second Edition, Hesse and Mumford, Pitman Publishing Corporation, 1964, Table 11.1
  15. ^ "The Development of Jet and Turbine Engines", 4th edition, Bill Gunston, ISBN 0 7509 4477 3, p. 192
  16. ^ Gas Turbine Engines. Aviation Week & Space Technology Source Book 2009. p. 119