General Electric GE36
|A mockup of the GE36 at the Musée aéronautique et spatial Safran|
|National origin||United States|
|Manufacturer||General Electric Aircraft Engines|
|Major applications||Boeing 7J7 (proposed)|
McDonnell Douglas MD-94X (proposed)
|Unit cost||$5 million (estimated, 1986 US dollars)|
|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, with its CFM International equal partner Snecma taking a 35 percent share of development.
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. GE then followed up with full-scale development testing of the GE36 starting in 1982. 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. At the Paris Air Show in mid-1985, Snecma announced that it had obtained a 35-percent stake in the engine program. Later in the decade, the 25,000-pound-force thrust (110-kilonewton) engine 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. The GE36 prototype then flew 25 times, accumulating over 41 hours of flight test time (out of a planned 75 hours) on a Boeing 727 from August 20, 1986 until mid-February of 1987, eventually reaching a flight speed of Mach 0.84 and altitude of 39,000 feet (12,000 metres). It also flight-tested on a McDonnell-Douglas MD-80 from May 18, 1987, initially using an 8-blade forward and 8-blade aft fan configuration, then being replaced with a 10-blade forward / 8-blade aft setup. 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. 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). 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. 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. McDonnell-Douglas reinstalled the GE36 engine onto the MD-80 testbed for additional flight tests in July/August 1988, and it flew that testbed airplane publicly at the Farnborough Air Show in September 1988 in the 10x8 blade configuration. GE36 testing on the MD-80 finished that month after 137 flights and nearly 240 flight hours. In total, there were 281 hours of flight tests between the two airplanes.
The downfall of this engine at the time was economic conditions (mostly a major drop in oil prices) post OPEC oil embargo. 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, and were expected to weigh less than 20 lb (9.1 kg) by the time the engine entered production. 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.
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. 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. The power turbine was a seven-stage (initially 6-stage) 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, so it did not require a reduction gearbox to drive the fan. The contra-rotating propellers spun at a maximum rotational speed of at least 1,393 rpm. 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.
The engine demonstrated an extremely low specific fuel consumption of 0.232 lbs/lb-thrust/hr, which GE claimed was over 20% more efficient than any of the existing turbofans on offer. 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. The regulatory compliance, however, caused a five-percent reduction in fuel efficiency compared to the most efficient fan configuration.
- Type: gearless, contra-rotating, pusher unducted fan with modified production F404 turbofan gas generator
- 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)
- Aft fan diameter (10 forward blade + 8 aft blade setup): 132.0 in (335 cm; 11.00 ft; 3.35 m)
- Aft fan diameter (8 forward blade + 8 aft blade setup): 128.0 in (325 cm; 10.67 ft; 3.25 m)
- Dry weight:
- Compressor: 3-stage axial flow, rotor speed 16,810 rpm
- Turbine: 1-stage low-pressure, 1-stage high-pressure
- Maximum thrust: 25,000 lbf (110 kN) @ 1,393 rpm
- Overall pressure ratio: 26:1
- Bypass ratio: 35
- Air mass flow: about 140 pounds-mass/second
- Turbine inlet temperature: 1,310 °F (710 °C)
- Specific fuel consumption: 0.232 pounds/pound-thrust/hour
- Thrust-to-weight ratio: 8:1
- Boeing 727 (testbed)
- Boeing 7J7 (proposed)
- McDonnell Douglas MD-81 UHB testbed
- McDonnell Douglas MD-94X (proposed)
- Air Transport World, 1986: Harrington estimated that production GE36 UDFs will cost $5 million each. CFM56s cost about $3.2 million today.
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- 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.
- GE engine test, December 1987, page 1
- Khalid et al. 2013, p. 4
- 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.
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- Hager & Vrabel 1988, pp. 93 to 97.
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- 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.
- 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.
- "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.
- Mongelluzzo, Bill (April 10, 1988). "McDonnell Douglas says UHB aircraft saves fuel". Air Cargo. Journal of Commerce. ISSN 1530-7557.
- 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.
- "Allison propfan clear for flight" (PDF). Flight International. Vol. 134 no. 4127. August 20, 1988. p. 5. ISSN 0015-3710.
- "Whatever happened to propfans?". Flight International. June 12, 2007. Archived from the original on March 24, 2012. Retrieved May 8, 2019.
- Unducted fan MD81 - SBAC Farnborough - 4 September 1988. Farnborough, England, United Kingdom: Phil Whalley (published March 14, 2011). September 4, 1988 – via YouTube.
- "Commercial aircraft of the world". Flight International. Vol. 134 no. 4134. October 8, 1988. p. 55. ISSN 0015-3710.
- Mongelluzzo, Bill (December 28, 1988). "McDonnell Douglas sets tests for propfan engine". Air Cargo. Journal of Commerce. ISSN 1530-7557.
- GE design report, page 163
- 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.
- "GE Reports – Honey I shrunk the World: How Materials Scientists Made the Globe Smaller".
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- Khalid et al. 2013, p. 15
- 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.
- GE design report, December 1987
- 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.
- "UDF: No sign of an order—yet" (PDF). Farnborough Report. Flight International. Vol. 134 no. 4131. September 17, 1988. p. 22. ISSN 0015-3710.
- GE engine test, December 1987, page 239
- "UDF prepared for flight" (PDF). World News. Flight International. Vol. 130 no. 4022. August 2, 1986. p. 2. ISSN 0015-3710.
- 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.
- Khalid et al. 2013, pp. 7 to 8
- Simpson et al. 1989, p. 8 to 9
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- "Farnborough quiet reflects sales bonanza". Air Transport World. Farnborough, England, United Kingdom. October 1988. pp. 16+. ISSN 0002-2543.
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- Donoghue, J. A. (March 1988). "McDonnell Douglas markets MD-90 transports with G.E. UDF power". Air Transport World. Vol. 25 no. 3. pp. 37+. ISSN 0002-2543.
- Hager, Roy V.; Vrabel, Deborah (1988). Advanced turboprop project. NASA SP-495. Lewis Research Center, Cleveland, Ohio: National Aeronautics and Space Administration (NASA) Scientific and Technical Information Division. hdl:2060/19890003194. OCLC 17508419. Archived (PDF) from the original on March 13, 2017. Retrieved February 2, 2019. Lay summary.
- GE Aircraft Engines, GE36 Project Department (December 1987). Full scale technology demonstration of a modern counterrotating unducted fan engine concept: Design report. NASA. hdl:2060/19900000732. OCLC 82995299 – via Internet Archive. Lay summary.
- GE Aircraft Engines, GE36 Project Department (December 1987). Full scale technology demonstration of a modern counterrotating unducted fan engine concept: Engine test. NASA. hdl:2060/19900000733. OCLC 82995299 – via Internet Archive. Lay summary.
- GE Aircraft Engines, GE36 Project Department (December 1987). Full scale technology demonstration of a modern counterrotating unducted fan engine concept: Component test. NASA. hdl:2060/19900000731. OCLC 82995299 – via Internet Archive. Lay summary.
- "Paris gives strong hints of changes to come". Air Transport World. Vol. 24. July 1987. pp. 18+. ISSN 0002-2543.
- Donoghue, J. A. (July 1987). "McDonnell Douglas opens UHB flight tests". Air Transport World. Vol. 24. pp. 36+. ISSN 0002-2543.
- Donoghue, J. A. (April 1987). "SuperFan opponents dispute timing; UDF tests advance". Air Transport World. Vol. 24. pp. 42+. ISSN 0002-2543.
- "Manufacturers positioning for coming competitive battles". Air Transport World. Vol. 23. September 1986. pp. 20+. ISSN 0002-2543.
- Donoghue, J. A. (September 1984). "G.E.'s unducted fan spices propfan stew". Air Transport World. Vol. 21. pp. 38+. ISSN 0002-2543.
|Wikimedia Commons has media related to General Electric GE36.|
- General Electric. UDF/GE36 engine: Executive summary. OCLC 55032766.
- Wilson, Douglas (February 2009). "Turboprop history: TPs continue their key role in bizav". Professional Pilot. pp. 72+. Archived from the original on November 29, 2010.
- Norris, Guy (June 12, 2007). "Green sky thinking - carbon credits and the propfan comeback?". Flight International. ISSN 0015-3710. Archived from the original on June 21, 2007. Retrieved January 28, 2019.
- Boeing UDF test footage. August 20, 1986 – via Vimeo.
- Bone, Dave (March 30 – April 1, 2011). DREAM: Validation of radical engine architecture systems. The alternative solution for a cleaner future (PDF). European Aeronautics Days (Aerodays 2011): Innovation for Sustainable Aviation in a Global Environment (sixth ed.). Madrid, Spain. Archived (PDF) from the original on March 2, 2018.
- Snecma/General Electric: GE36 UDF. Safran Museum. November 6, 2012.
- "Dowty to build UDF blades". World News. Flight International. Vol. 132 no. 4085. Cheltenham, England, United Kingdom. October 24, 1987. p. 3. ISSN 0015-3710.
- Vartabedian, Ralph (February 4, 1988). "McDonnell unveils plane with revolutionary engine". Los Angeles Times. ISSN 0458-3035. OCLC 3638237.
- Harris, Robert W.; Cuthbertson, R. D. (June 29 – July 2, 1987). UDF/727 flight test program. Joint Propulsion Conference (23rd ed.). San Diego, California, USA. doi:10.2514/6.1987-1733. OCLC 80141408.
- "Boeing jetliner prototypes and testbeds: 727-63 General Electric unducted fan testbed, c/n 19846". Air-and-Space.com. Retrieved May 10, 2019.
- Ziemianski, Joseph A.; Whitlow, John B., Jr. (August 28 – September 2, 1988). NASA/industry advanced turboprop technology program (PDF). Conference of the International Council of Aeronautical Sciences (16th ed.). Jerusalem, Israel. OCLC 4433879345.