General Electric GE36

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Maquette UDF - Musée Safran (cropped).jpg
A mockup of the GE36 at the Musée aéronautique et spatial Safran
Type Unducted fan
National origin United States
Manufacturer General Electric Aircraft Engines
First run 1986
Major applications Boeing 7J7 (proposed)
McDonnell Douglas MD-94X (proposed)
Unit cost $5 million (estimated, 1986 US dollars)[1]
Developed from General Electric F404

The General Electric GE36 was an experimental aircraft engine, a hybrid between a turbofan and a turboprop, known as an unducted fan (UDF) or propfan. The GE36 was developed by General Electric Aircraft Engines,[2] with its CFM International equal partner Snecma taking a 35 percent share of development.[3]


General Electric started performing studies and component test work on the concept that would become the UDF in 1981, based on the initial results of early National Aeronautics and Space Administration (NASA) propfan technology studies that the aerospace agency first released to engine makers in 1980.[4] GE then followed up with full-scale development testing of the GE36 starting in 1982.[5] The company revealed its work to the NASA in December 1983, which quickly gave test funding for the concept, as NASA's own propfan research efforts were advancing at a slower pace and were dependent on additional grants from the U.S. Congress. GE disclosed the engine's development to the public in 1984.[6] At the Paris Air Show in mid-1985, Snecma announced that it had obtained a 35-percent stake in the engine program.[3] Later in the decade, the 25,000-pound-force thrust (110-kilonewton) engine[7] became the power plant of choice for proposed aircraft such as the Boeing 7J7 twin-aisle airliner and the MD-91 and MD-92 derivatives of McDonnell-Douglas's popular MD-80 single-aisle airplane.

The engine underwent 2,500 hours of model scale testing, after which a prototype was built. The prototype engine was ground-tested for 162 hours.[8] The GE36 prototype then flew 25 times,[9] accumulating over 41 hours of flight test time (out of a planned 75 hours) on a Boeing 727 from August 20, 1986[10] until mid-February of 1987, eventually reaching a flight speed of Mach 0.84 and altitude of 39,000 feet (12,000 metres).[11] It also flight-tested on a McDonnell-Douglas MD-80 from May 18, 1987,[12] initially using an 8-blade forward and 8-blade aft fan configuration, then being replaced with a 10-blade forward / 8-blade aft setup.[13] Despite being quieter in that configuration, the engine was reverted to the original 8x8 configuration because of a mechanical problem. GE also confirmed that for production, there would be more blades than on the demonstrator engine, and the number of blades on the front fan would be different from the number on the back fan.[14] Through April 1988, the MD-80 testbed had performed 93 flights and 165 flight test hours, cruising at a speed up to Mach 0.865 and an altitude of 37,000 feet (11,000 metres).[15] The totals included more than 20 customer demonstration flights that hosted 110 executives from 35 airlines and four leasing companies, plus 70 representatives of media, the United States military, suppliers, and other airline manufacturers.[16] The general opinion that the ride quality was little different than a normal flight, except for light vibration in the back seat during takeoff and climb.[17] McDonnell-Douglas reinstalled the GE36 engine onto the MD-80 testbed for additional flight tests in July/August 1988,[18] and it flew that testbed airplane publicly at the Farnborough Air Show in September 1988[19][20] in the 10x8 blade configuration.[21] GE36 testing on the MD-80 finished that month after 137 flights and nearly 240 flight hours.[22] In total, there were 281 hours of flight tests between the two airplanes.[8]

An early model of NASA/GE Unducted Fan

The downfall of this engine at the time was economic conditions (mostly a major drop in oil prices) post OPEC oil embargo.[citation needed] Even though these engines never made it past development and prototype testing, GE has retained the carbon composite technology behind the lightweight fan blades, which during the prototype/testing phase weighed 22.5 and 21.5 lb (10.2 and 9.8 kg) each on the front and back propellers, respectively,[23] and were expected to weigh less than 20 lb (9.1 kg) by the time the engine entered production.[24] Carbon fiber blades are currently being used in engines (General Electric GE90 and General Electric GEnx) that power the Boeing 747, Boeing 777, and Boeing 787 Dreamliner.[25][26]


A General Electric F404 military turbofan was used as the basis for the GE36 prototype. The F404 mixed exhaust stream discharged through a turbine which drove two contra-rotating stages of fans. Although the demonstrator engines had 8x8 and 10x8 fan blade configurations, the most efficient setup that was tested had a 12x10 blade configuration.[27] The scimitar shape of the fan rotor blades can operate at high velocities to match turbojet or turbofan speeds, allowing the engine to power the proposed Boeing 7J7 airliner at a Mach 0.83 cruise speed.[28] The power turbine was a seven-stage (initially 6-stage)[29] turbine plus inlet and outlet guide vanes. The fourteen turbine blade rows rotated alternate rows in opposite directions. Each stage was a pair of rotors; there were no stators. The counter-rotating turbine ran at half the rpm of a conventional turbine,[29] so it did not require a reduction gearbox to drive the fan.[30] The contra-rotating propellers spun at a maximum rotational speed of at least 1,393 rpm.[7] A new core instead of the off-the-shelf F404 was being constructed to increase efficiency, and the compressor, combustor, and turbine had all been run separately by late 1988.[31]

The engine demonstrated an extremely low specific fuel consumption of 0.232 lbs/lb-thrust/hr,[32] which GE claimed was over 20% more efficient than any of the existing turbofans on offer.[33] The engine configuration selected for the MD-91 and MD-92 was designed to meet the Chapter 4 community noise standards of the International Civil Aviation Organization's (ICAO's) Committee on Aviation Environmental Protection (CAEP), which would go into effect in 2006 and be a reduction of ten effective perceived noise decibels (EPNdB) from the existing Chapter 3 standards that were established in 1977.[34] The regulatory compliance, however, caused a five-percent reduction in fuel efficiency compared to the most efficient fan configuration.[35]


Data from GE engine test, page 17

General characteristics

  • Type: gearless, contra-rotating, pusher unducted fan with modified production F404 turbofan gas generator
  • Length:
  • Diameter: 76.4 in (194 cm; 6.37 ft; 1.94 m) maximum nacelle diameter
  • Forward fan diameter: 140.0 in (356 cm; 11.67 ft; 3.56 m)[36]
  • Aft fan diameter (10 forward blade + 8 aft blade setup): 132.0 in (335 cm; 11.00 ft; 3.35 m)[36]
  • Aft fan diameter (8 forward blade + 8 aft blade setup): 128.0 in (325 cm; 10.67 ft; 3.25 m)[36]
  • Dry weight:


  • Compressor: 3-stage axial flow, rotor speed 16,810 rpm
  • Turbine: 1-stage low-pressure, 1-stage high-pressure



A GE36 on a MD-81 demonstrator at Farnborough Airshow 1988

See also[edit]

Comparable engines

Related lists


  1. ^ Air Transport World, 1986: Harrington estimated that production GE36 UDFs will cost $5 million each. CFM56s cost about $3.2 million today.
  2. ^ Schmitman, Craig (1989). Ultra high bypass jet engine propfan technology. – via YouTube.
  3. ^ a b "Propfans ready by 1990". Paris Report. Flight International. June 8, 1985. p. 5. Archived (PDF) from the original on September 25, 2014. Retrieved March 28, 2019.
  4. ^ Haggerty, James J. (August 1987). "Toward future flight". Spinoff (PDF) (1987 ed.). NASA. pp. 30–33. Archived from the original on April 12, 2009.
  5. ^ Sutcliffe, Peter L. (June 18, 1986). "The Boeing 7J7 advanced technology airplane: Keynote speech to the 1986 American Control Conference" (PDF). IEEE Control Systems Magazine. Seattle, Washington, USA: IEEE (published February 1987). 7 (1): 9–15. doi:10.1109/MCS.1987.1105251. ISSN 0272-1708. OCLC 4631908460.
  6. ^ Banks, Howard (May 7, 1984). "The next step: Jets drove propellers from the skies. But radical designs are bringing props back, creating engines that promise jetlike speeds and enormous fuel savings" (PDF). Forbes. pp. 31–33 – via NASA Langley Research Center Cultural Resources Geographic Information Systems (GIS) Team.
  7. ^ a b GE engine test, December 1987, page 1
  8. ^ a b Khalid et al. 2013, p. 4
  9. ^ a b Sutcliffe, Peter L. (November 13, 1987). The Boeing 7J7—The evolution of technology and design. International Pacific Air and Space Technology Conference and Exposition. SAE 1987 Transactions: Aerospace. 96. Melbourne, Australia: SAE International (published September 1988). pp. 6.1757–6.1768. doi:10.4271/872405. ISSN 0096-736X. JSTOR 44473078. OCLC 939484633.
  10. ^ "GE's UDF flies again" (PDF). Air Transport. Flight International. Vol. 130 no. 4027. Mojave, California, USA. September 6, 1986. p. 23. ISSN 0015-3710.
  11. ^ Hager & Vrabel 1988, pp. 93 to 97.
  12. ^ Warwick, Graham (August 15, 1987). "UHB: The acid test". Flight International. pp. 22–23. Retrieved March 22, 2019.
  13. ^ Moxon, Julian (September 5, 1987). "Boeing delays 7J7 certification". Air Transport. Flight International. Vol. 132 no. 4078. Washington, D.C., USA. p. 4. ISSN 0015-3710.
  14. ^ Moxon, Julian (December 19, 1987). "McDonnell Douglas ready to launch UDF airliners" (PDF). Air Transport. Flight International. Vol. 132 no. 4093. Long Beach, California, USA. p. 6. ISSN 0015-3710.
  15. ^ "MDC propfan tests complete" (PDF). Air Transport. Flight International. Vol. 133 no. 4109. Edwards Air Force Base, California, USA. April 16, 1988. p. 7. ISSN 0015-3710.
  16. ^ Mongelluzzo, Bill (April 10, 1988). "McDonnell Douglas says UHB aircraft saves fuel". Air Cargo. Journal of Commerce. ISSN 1530-7557.
  17. ^ Moxon, Julian (February 13, 1988). "Douglas shows off propfan demonstrator". World News. Flight International. Vol. 133 no. 4100. Long Beach, California, USA. p. 3. ISSN 0015-3710.
  18. ^ "Allison propfan clear for flight" (PDF). Flight International. Vol. 134 no. 4127. August 20, 1988. p. 5. ISSN 0015-3710.
  19. ^ "Whatever happened to propfans?". Flight International. June 12, 2007. Archived from the original on March 24, 2012. Retrieved May 8, 2019.
  20. ^ Unducted fan MD81 - SBAC Farnborough - 4 September 1988. Farnborough, England, United Kingdom: Phil Whalley (published March 14, 2011). September 4, 1988 – via YouTube.
  21. ^ "Commercial aircraft of the world". Flight International. Vol. 134 no. 4134. October 8, 1988. p. 55. ISSN 0015-3710.
  22. ^ Mongelluzzo, Bill (December 28, 1988). "McDonnell Douglas sets tests for propfan engine". Air Cargo. Journal of Commerce. ISSN 1530-7557.
  23. ^ GE design report, page 163
  24. ^ Hamilton, Martha M. (February 8, 1987). "Firms give propellers a new spin". Business. Washington Post. pp. H1, H4. Archived (PDF) from the original on March 26, 2015.
  25. ^ "GE Reports – Honey I shrunk the World: How Materials Scientists Made the Globe Smaller".
  26. ^ GE Reports (April 29, 2009). GE Aviation - Aircraft engine history and technology - Jet engine – via YouTube.
  27. ^ Khalid et al. 2013, p. 15
  28. ^ Air Transport World, 1986: G.E., however, insisted that open rotors' efficiency drops off at a much higher speed. Gordon said Boeing has G.E.'s and its own results from UDF windtunnel tests up to Mach 0.9 and continues to list the UDF as the baseline engine on the 7J7 that has a design cruise speed of Mach 0.83. 'Boeing is not crazy,' he told ATW.
  29. ^ a b GE design report, December 1987
  30. ^ Sweetman, Bill (September 2005). "The short, happy life of the Prop-fan: Meet the engine that became embroiled in round one of Boeing v. Airbus, a fight fueled by the cost of oil". Air & Space/Smithsonian Magazine. 20 (3). pp. 42–49. ISSN 0886-2257. OCLC 109549426. Archived from the original on August 14, 2017. Retrieved January 28, 2019.
  31. ^ "UDF: No sign of an order—yet" (PDF). Farnborough Report. Flight International. Vol. 134 no. 4131. September 17, 1988. p. 22. ISSN 0015-3710.
  32. ^ a b GE engine test, December 1987, page 239
  33. ^ "UDF prepared for flight" (PDF). World News. Flight International. Vol. 130 no. 4022. August 2, 1986. p. 2. ISSN 0015-3710.
  34. ^ Spencer, Jessica C. (October 25, 2017). "Stage 5 aircraft noise standards approved in US – what does it mean for airports?". Archived from the original on March 28, 2019. Retrieved March 28, 2019.
  35. ^ Khalid et al. 2013, pp. 7 to 8
  36. ^ a b c Simpson et al. 1989, p. 8 to 9


External links[edit]