General Electric (GE) 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.[5] GE then followed up with full-scale development testing of the GE36 starting in 1982.[6] NASA gave GE a $20.4 million contract in February 1984 to study the concept[7] after the company showed the agency its work in December 1983, as NASA's own propfan research efforts were advancing at a slower pace and were dependent on additional grants from the U.S. Congress.
A full-scale model of the NASA/GE unducted fan at the 1984 Farnborough Air Show.
Around the same time, GE was negotiating with Boeing, which felt that the UDF technology could be useful for short-haul airliners, to test a demonstration engine on a Boeing 727 testbed aircraft.[8] Agreement to flight test the UDF was reached in April, with flights beginning in late 1986 to assess a 25,000 pounds-force (110kN) demonstrator based on a General Electric F404 core. The engine would have a pair of six-stage contra-rotating free turbines, each with large diameters running at slow speeds, and they would be connected directly to a couple of eight-blade, 12-foot diameter (3.7m) unducted fans.[9] The effective bypass ratio (BPR) was estimated to be about 30:1 for the UDF, which was much larger than the 6:1 bypass ratios of modern turbofans at the time, but less than propeller/turboprop BPRs of approximately 50:1. The optimal mission would be on 1,000 nautical miles (1,200mi; 1,900km) flights with a cruise speed of Mach 0.75.[10] In May 1984, Boeing began testing a GE contra-rotating model test rig in its 9 by 9ft (2.7 by 2.7m) low-speed wind tunnel and 8 by 12ft (2.4 by 3.7m)transonic wind tunnel.[11]
GE unveiled a full-scale model of the engine at the Farnborough Air Show in September, promising a 30-percent reduction in fuel consumption compared to current airliner engines without decreasing the cruise speed. A dozen airlines "invited themselves" to see GE's UDF test facilities near Cincinnati, Ohio, claimed the engine maker, but not just due to the UDF's higher fuel efficiency. Airlines also appreciated the UDF's lack of a gearbox, which transfers power from the turbine to the propeller while allowing both to run at their respective optimal rotational speeds, but was difficult to design reliably for high speed and power. They also liked that the UDF had contra-rotating fans, as opposed to the single-rotating fans that NASA was primarily studying. The double fans kept the diameter for a 140-seat airliner significantly smaller than the 20ft (6.1m) diameters the airlines feared.[12] The unducted fan demonstrator would have a diameter of 11ft 8in (3.56m), a power rating of 20,000 horsepower (15,000 kilowatts), and a thrust rating of 25,000lbf (110kN). The UDF demonstrator, which would have enough power to drive a 200-seat airliner, was intentionally sized to be larger than the UDF engines that GE was planning for production. The UDF production engines would be 10ft (3.0m) in diameter, produce 10,000hp (7,500kW), and power airplanes in the 120-160 seat market.[13] At the Paris Air Show in mid-1985, Snecma announced that it had obtained a 35-percent stake in the engine program.[4] Later in the decade, the GE36 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 GE36 UDF demonstrator on the ground test stand in 1985.
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.[14] The GE36 prototype then flew 25 times,[15] accumulating over 41 hours of flight test time (out of a planned 75 hours) on a Boeing 727 from August 20, 1986[16] until mid-February 1987, eventually reaching a flight speed of Mach 0.84 and altitude of 39,000 feet (12,000 metres).[17] In April 1987, Boeing formally selected the GE36 as the powerplant for the Boeing 7J7, deeming the IAE SuperFan ultra-high bypass (UHB) geared turbofan as less fuel efficient[18] and the Pratt & Whitney/Allison 578-DX geared propfan as insufficiently powered.[19] At the Paris Air Show in June 1987, GE and Snecma noted that they were building the components for a product design engine that would test on a Boeing 727 in 1989.[20] However, Boeing in August 1987 postponed the service entry date of the 7J7 from 1992 to 1993, and then it postponed the target date indefinitely in December 1987.[21]
GE's proof-of-concept engine was installed on a McDonnell Douglas MD-80 on April 5, 1987,[22] and its first flight on the MD-80 testbed was on May 18, 1987.[23] Initially the engine had an 8-blade forward and 8-blade aft fan configuration, and then it was replaced on the testbed by the second GE36 demonstrator engine, which had a 10-blade forward / 8-blade aft setup[24] and completed 33 hours of flight tests beginning on August 14, 1987.[25] Despite being quieter in that configuration, the engine was swapped back 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.[26]
After the testbed was reconfigured with the 8x8 engine setup, McDonnell Douglas conducted 22 customer demonstration flights from the Long Beach Airport.[27] These customer demonstrations took place between January 22 and February 26 of 1988. The flights, which typically lasted about an hour and reached a cruise speed of Mach 0.76, hosted the prime minister of Finland,[28] 110 executives from 35 airlines and four leasing companies, and 70 representatives of media, the United States military, suppliers, and other airline manufacturers.[29] The general opinion was that the ride quality was little different than a normal flight, except for light vibration in the back seat during takeoff and climb.[30] On March 25, 1988, McDonnell Douglas declared the flight test program complete.[27] 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).[31]
McDonnell Douglas reinstalled the GE36 engine onto the MD-80 testbed for additional flight tests in July 1988.[32] The testbed airplane was then flown across the Atlantic Ocean, leaving its home test airfield of Edwards Air Force Base in California to stop in Minneapolis, Minnesota, Gander, Newfoundland, Canada, and Keflavik, Iceland before ending the 4,700nmi trip (5,400mi; 8,700km) in Farnborough Airport in England on August 23. The trip was made to perform daily public demonstration flights at the Farnborough Air Show on September 4–11, 1988.[33] Private flight demonstrations for invited airline executives were to be given before the air show, and McDonnell Douglas was considering flying the testbed to Western Europe before returning to the US.[34] At the air show, McDonnell Douglas and GE began marketing discussions with seven airlines in the US and six in western Europe; they hoped to gain about 100 airline commitments by mid-1989 to launch the MD-91 and MD-92 programs, with entry into service in 1993 first for the MD-91, and then the MD-92 entering service a half-year later.[35] GE36 testing on the MD-80 finished that month after 137 flights and nearly 240 flight hours.[36] In total, there were 281 hours of flight tests between the two airplanes.[14]
With demonstrator flight testing completed, the focus moved to construction of a new core (instead of the off-the-shelf F404) to increase efficiency. The compressor, combustor, and turbine had all been run separately by late 1988,[37] and by mid-1989 the new core engine had been tested for about 50 hours. At the time of the project cancellation later in 1989, GE and Snecma were working on the design engineering of a full gas generator and a product propulsor.[38]
The GE36 UDF demonstrator installed on the Boeing 727 testbed in 1986.
A General Electric F404 military turbofan on loan from the American government was used as the basis for the GE36 prototype.[43] 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.[44] The scimitar shape of the fan rotor blades could 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.[45] The production blades for the MD-91/MD-92 versions of the engine were to be designed for Mach 0.78–0.80 cruise.[46]
The UDF fan blades were 40in (100cm) in length, and the Rohr Industries-made rotating cowls that fit around the base of the blades were 62in (160cm) in diameter.[47] The blades for the initial tests were manufactured directly by General Electric, but the blades for the flight tests were then made by local Ohio manufacturer Hartzell Propeller.[48] For the production engines, the blades were to be made by British composite propeller specialist Dowty Rotol.[49] The maximum fan diameter for the UDF demonstrator was 140in (356cm),[50] while the maximum diameter for the UDF production engines was planned to be 128in (325cm).[44] During the prototype/testing phase, the fan blades weighed 22.5 and 21.5lb (10.2 and 9.8kg) each on the front and back propellers, respectively,[51] but they were expected to weigh less than 20lb (9.1kg) by the time the engine entered production.[52]
While the GE36 demonstrator had a rated thrust of 25,000lbf (110kN), the GE36 family of engines would offer a range covering 12,000 to 30,000lbf (53 to 133kN) of thrust. The engine was initially sized to produce 14,000lbf (62kN) for the MD-91X and 20,000–22,000lbf (89–98kN) for the 7J7 and MD-92X,[53] but the thrust requirements were later changed to 22,000lbf (98kN) and 25,000lbf (110kN), respectively.[54]
The power turbine was a six-stage turbine plus inlet and outlet guide vanes.[55]:46 The twelve turbine blade rows rotated alternate rows in opposite directions. Each stage was a pair of rotors; there were no stators (static vanes), which usually follow the single-rotor section to straighten out the flow. The front propeller and the front half of each stage are attached to a rotating outer casing that encloses the turbine rotor blades, while the back propeller and the back half of each stage are attached conventionally to a central shaft. The counter-rotating turbine can run at half the rpm of a conventional turbine, since counter-rotation doubles the relative velocity, so the engine did not require a reduction gearbox to drive the fan.[56] The GE36 had a hub-to-blade tip radius ratio of 0.425,[57] which as a gearless design reflected about a 75 percent higher value than for geared propfan designs.[58] This characteristic occurred because the hub had to enclose a large turbine diameter; due to the low rotational speed demanded by the contra-rotating propellers, the turbine had to be wider than usual to generate enough power.[59] GE's UDF had a bypass ratio of 35, which was about halfway between the IAE SuperFan's BPR of 17 and the PW-Allison 578-DX's BPR of 56.[15] The contra-rotating propellers spun at a maximum rotational speed of at least 1,393 rpm.[60]
The engine demonstrated an extremely low specific fuel consumption (SFC) of 0.232lb/(lbf⋅h) (6.6g/(kN⋅s)) at ground level,[61] which GE claimed was over 20% more efficient than any of the existing turbofans on offer.[62] GE had also predicted a cruise SFC of 0.49 for the demonstrator engine; however, the cruise SFC would drop to 0.40-0.41 with a new gas generator design called "Supercore,"[63] compared with 0.56 for existing turbofans.[64] The two-spool core of the gas generator would have a pressure ratio of about 36.[65]:21 Snecma was to design the high-pressure compressor (HPC) and the combustion chamber.[66] 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.[67] The regulatory compliance, however, caused a five-percent reduction in fuel efficiency compared to the most efficient fan configuration.[68]
The McDonnell DouglasMD-90 is an American five-abreast single-aisle airliner developed by McDonnell Douglas from its successful model MD-80. The airliner was produced by the developer company until 1997 and then by Boeing Commercial Airplanes. It was a stretched derivative of the MD-80 and thus part of the DC-9 family. After the more fuel-efficient IAE V2500 high-bypass turbofan was selected, Delta Air Lines became the launch customer on November 14, 1989. The MD-90 first flew on February 22, 1993, and the first delivery was in February 1995 to Delta.
The General Electric GE90 is a family of high-bypass turbofan aircraft engines built by GE Aerospace for the Boeing 777, with thrust ratings from 81,000 to 115,000 pounds-force. It entered service with British Airways in November 1995. It is one of three options for the 777-200, -200ER, and -300 versions, and the exclusive engine of the -200LR, -300ER, and 777F. It was the largest jet engine, until being surpassed in January 2020 by its successor, the 110,000 lbf (490 kN) GE9X, which has a 6-inch (15 cm) larger diameter fan. However, the GE90-115B, the most recent variant, is rated for a higher thrust than the GE9X.
The Rolls-Royce Trent is a family of high-bypass turbofans produced by Rolls-Royce. It continues the three spool architecture of the RB211 with a maximum thrust ranging from 61,900 to 97,000 lbf . Launched as the RB-211-524L in June 1988, the prototype first ran in August 1990. Its first variant is the Trent 700 introduced on the Airbus A330 in March 1995, then the Trent 800 for the Boeing 777 (1996), the Trent 500 for the A340 (2002), the Trent 900 for the A380 (2007), the Trent 1000 for the Boeing 787 (2011), the Trent XWB for the A350 (2015), and the Trent 7000 for the A330neo (2018). It has also marine and industrial variants like the RR MT30.
A propfan, also called an open rotor engine, open fan engine or unducted fan, is a type of aircraft engine related in concept to both the turboprop and turbofan, but distinct from both. The design is intended to offer the speed and performance of a turbofan, with the fuel economy of a turboprop. A propfan is typically designed with a large number of short, highly twisted blades, similar to the (ducted) fan in a turbofan engine. For this reason, the propfan has been variously described as an "unducted fan" (UDF) or an "ultra-high-bypass (UHB) turbofan".
The Boeing 7J7 was an American short- to medium-range airliner proposed by American aircraft manufacturer Boeing in the 1980s. It would have carried 150 passengers and was touted as the successor to the successful Boeing 727. It was initially planned to enter service in 1992. This was intended as a highly fuel-efficient aircraft employing new technologies, but it was postponed indefinitely as the price of oil dropped during the 1980s.
The Tupolev Tu-334 was a Russian short-to-medium range airliner project that was developed to replace the aging Tu-134s and Yak-42s in service around the world. The airframe was based on a shortened Tu-204 fuselage and a scaled-down version of that aircraft's wing. Unlike the Tu-204, however, the Tu-334 has a T-tail and engines mounted on the sides of the rear fuselage instead of under the wings. With the nationalisation of the Russian aircraft companies in 2009 to form United Aircraft Corporation it was decided not to continue with the programme.
The McDonnell Douglas MD-94X was a planned propfan-powered airliner, intended to begin production in 1994. Announced in January 1986, the aircraft was to seat between 160 and 180 passengers, possibly using a twin-aisle configuration. An all-new design that was investigated internally since at least 1984, the MD-94X was developed in the mid-1980s to compete with the similar Boeing 7J7. The price of oil would have to be at least US$1.40 per gallon for McDonnell Douglas to build the plane, though. Configuration was similar to the MD-80, but advanced technologies such as canard noseplanes, laminar and turbulent boundary layer control, side-stick flight control, and aluminum-lithium alloy construction were under consideration. Airline interest in the brand-new propfan technology was weak despite claims of up to a 60% reduction in fuel use, and both aircraft were canceled.
IAE International Aero Engines AG is a Zürich-registered joint venture aeroengine manufacturing company.
The Yakovlev Yak-46 was a proposed aircraft design based on the Yak-42 with two contra-rotating propellers on the propfan located at the rear. The specification of the Samara turbofans was in the 11,000 kg thrust range. Though proposed in the 1990s, production of the Yak-46 never commenced.
The Progress D-27 is a three-shaft propfan engine developed by Ivchenko Progress, and manufactured by Motor Sich in Ukraine. The gas generator was designed using experience from the Lotarev D-36 turbofan. The D-27 engine was designed to power more-efficient passenger aircraft such as the abandoned Yakovlev Yak-46 project, and it was chosen for the Antonov An-70 military transport aircraft. As of 2019, the D-27 is the only contra-rotating propfan engine to enter service.
The General Electric GE38 is a gas turbine developed by GE Aviation for turboprop and turboshaft applications. It powers the Sikorsky CH-53K King Stallion as the T408.
The Lycoming ALF 502/LF 507 is a geared turbofan engine produced by Lycoming Engines, AlliedSignal, and then Honeywell Aerospace. The U.S. military designation for the ALF 502 is YF102.
The Pratt & Whitney/Allison 578-DX was an experimental aircraft engine, a hybrid between a turbofan and a turboprop known as a propfan. The engine was designed in the 1980s to power proposed propfan aircraft such as the Boeing 7J7 and the MD-91 and MD-92 derivatives of the McDonnell Douglas MD-80. As of 2019, it is still one of only four different contra-rotating propfan engines to have flown in service or in flight testing.
The Turbomeca Astafan is a single-spool, variable-pitch turbofan engine developed from the Turbomeca Astazou. Despite successful flight-testing, an efficient, quiet and clean design and some commercial interest, the Astafan never entered series production. The engines were only flown on the Fouga 90 prototype and Turbomeca's two test aircraft.
MPC 75 was an aircraft project of MPC Aircraft GmbH, a subsidiary of Deutsche Airbus. Work on the project was done mainly between 1988 and 1992 in Hamburg, Germany. Predevelopment work was finished, however the project never got the "go ahead" and never made it into full development.
The IAE V2500SF SuperFan was a design study for a high-bypass geared turbofan derived from the IAE V2500. It was offered as the primary engine option for the Airbus A340 in January 1987. Although several customers signed preliminary contracts for this variant, the International Aero Engines board decided in April 1987 to stop the development of the SuperFan, which forced Airbus to partly re-design the A340.
The Progress D-236 was an experimental aircraft engine, a hybrid between a turbofan and a turboprop known as a propfan. Also known as the Lotarev D-236T, the three-shaft geared engine was designed in the 1980s and 1990s to power proposed propfan aircraft such as the Tupolev Tu-334, Ilyushin Il-118, and Ilyushin Il-88.
The Kuznetsov NK-93 was a civilian aircraft engine, a hybrid between a turbofan and a turboprop known as a propfan. The engine was also unique in having a separate duct around the contra-rotating propellers, as most other propfans are unducted. Once described in a respected aviation encyclopedia as "potentially the most fuel-efficient aircraft jet engine ever to be tested", the NK-93 was targeted for derivatives of Soviet/Russian airliners such as the Ilyushin Il-96, Tupolev Tu-204, and Tupolev Tu-330. Five in-flight engine tests were conducted on the NK-93 from December 2006 to December 2008.
The Allison T56 turboprop engine has been developed extensively throughout its production run, the many variants are described by the manufacturer as belonging to four main series groups.
The Rolls-Royce RB529 Contrafan was a high-thrust aircraft engine proposed by Rolls-Royce in the 1980s to power long-range wide-body airliners.
↑ Haggerty, James J. (1987-08-01). "Toward future flight". Spinoff(PDF) (1987ed.). NASA (published August 1987). pp.30–33. Archived from the original on April 12, 2009.
1 2 3 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. SAE Technical Paper Series. Vol.96. Melbourne, Australia: SAE International (published September 1988). pp.6.1757–6.1768. doi:10.4271/872405. ISSN0096-736X. JSTOR44473078. OCLC939484633.
↑ "GE's UDF flies again"(PDF). Air Transport. Flight International. Vol.130, no.4027. Mojave, California, USA. September 6, 1986. p.23. ISSN0015-3710.
↑ Lewerenz, William T. (June 29 – July 2, 1987). "UHB demonstrator flight test program". 23rd Joint Propulsion Conference. Joint Propulsion Conference (23rded.). San Diego, California, USA. doi:10.2514/6.1987-1732.
↑ Warwick, Graham (August 15, 1987). "UHB: The acid test". Flight International. pp.22–23. Retrieved March 22, 2019.
↑ 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.
↑ Whitlow, John B., Jr.; Sievers, G. Keith (October 1988). "Building the foundation". Aircraft. Aerospace America. p.15. ISSN0740-722X– via Nexis Uni.{{cite magazine}}: CS1 maint: multiple names: authors list (link)
↑ Henne, P. A. (July 31 – August 2, 1989). "MD-90 transport aircraft design". Aircraft Design and Operations Meeting. AIAA/AHS/ASEE Aircraft Design, Systems and Operations Conference. Seattle, Washington, USA. doi:10.2514/6.1989-2023.
Khalid, S. Arif; Lurie, David; Breeze-Stringfellow, Andrew; Wood, Trevor; Ramakrishnan, Kishore; Paliath, Umesh; Wojno, John; Janardan, Bangalore; Goerig, Trevor; Opalski, Anthony; Barrett, Jack (May 2013). "FAA CLEEN program open rotor aeroacoustic technology non-proprietary report"(PDF). Federal Aviation Administration. General Electric. Archived(PDF) from the original on 8 July 2018. Retrieved 8 July 2018.
Donelson, John E.; Lewerenz, William T.; Durbin, Roger T. (July 11–13, 1988). UHB demonstrator flight test program: The final step. Joint Propulsion Conference (24thed.). Boston, Massachusetts, USA. doi:10.2514/6.1988-2807.
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. OCLC17508419. Archived(PDF) from the original on March 13, 2017. Retrieved February 2, 2019. alternate url
Harris, Robert W.; Cuthbertson, R. D. (June 29 – July 2, 1987). "UDF/727 flight test program". 23rd Joint Propulsion Conference. Joint Propulsion Conference (23rded.). San Diego, California, USA. doi:10.2514/6.1987-1733. OCLC80141408.
GE Canada (April 14, 1987). "GE aerospace: Announcing a dramatic breakthrough in aircraft technology: The propellor". Report on Business. The Globe and Mail. Toronto, Ontario, Canada. p.B3. ISSN0319-0714. With potential fuel savings of up to 45% over the best high bypass turbofans, and at speeds of Mach .8, the UDF will mean major cost reductions and greater profitability for the airlines. This engine can also be scaled to any thrust size, to serve a wide variety of aircraft.
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