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Wikipedia

Propfan

January 17, 2023

Not to be confused with turboprop or turbofan.

A propfan, also called an open rotor engine, or unducted fan (as opposed to a ducted 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."

A closeup of the PW–Allison 578-DX propfan demonstrator, installed on the port side of a McDonnell Douglas MD-80 testbed.

Definition

 
Propulsive efficiency comparison for various gas turbine engine configurations

In the 1970s, Hamilton Standard described its propfan as "a small diameter, highly loaded multiple bladed variable pitch propulsor having swept blades with thin advanced airfoil sections, integrated with a nacelle contoured to retard the airflow through the blades thereby reducing compressibility losses and designed to operate with a turbine engine and using a single stage reduction gear resulting in high performance."[1] In 1982, the weekly aviation magazine Flight International defined the propfan as a propeller with 8–10 highly swept blades that cruised at a speed of 390–480 knots (450–550 miles per hour; 720–890 kilometres per hour),[2] although its definition evolved a few years later with the emergence of contra-rotating propfans.[3]

In 1986, British engine maker Rolls-Royce used the term open rotor as a synonym for the original meaning of a propfan. This action was to delineate the propfan engine type from a number of ducted engine proposals at the time that had propfan in their names.[4] By the 2000s, open rotor (OR) became a preferred term for propfan technology in research and news reports, with contra-rotating open rotor (CROR) also occasionally being used to distinguish between single-rotation propfans. As of 2015, the European Aviation Safety Agency (EASA) defined an open rotor concretely (but broadly) as "a turbine engine fan stage that is not enclosed within a casing;" in contrast, it had only a working definition of an open rotor engine (the more commonly used term for propfan in the 21st century), calling it "a turbine engine featuring contra-rotating fan stages not enclosed within a casing." The engine uses a gas turbine to drive an unshrouded (open) contra-rotating propeller like a turboprop, but the design of the propeller itself is more tightly coupled to the turbine design, and the two are certified as a single unit.[5]

El-Sayed differentiates between turboprops and propfans according to 11 different criteria, including number of blades, blade shape, tip speed, bypass ratio, Mach number, and cruise altitude.[6]

History

About a decade after German aerospace engineers began exploring the idea of using swept wings to reduce drag on transonic speed aircraft, Hamilton Standard in the 1940s attempted to apply a similar concept to engine propellers. It created highly swept propeller blades with supersonic tip speeds, so that engines with exposed propellers could power aircraft to speeds and cruising altitudes only attained by new turbojet and turbofan engines. Early tests of these blades revealed then-unresolvable blade flutter and blade stress problems, and high noise levels were considered another obstacle. The popularity of turbojets and turbofans curtailed research in propellers, but by the 1960s, interest increased when studies showed that an exposed propeller driven by a gas turbine could power an airliner flying at a speed of Mach 0.7–0.8 and at an altitude of 35,000 feet (11,000 metres). The term propfan was created during this period.[7]

One of the earliest engines that resembled the propfan concept was the 4,710 pounds-force (21.0 kilonewtons) Metrovick F.5, which featured twin contra-rotating fans—14 blades in the fore (front) fan and 12 blades in the aft (back) fan—at the rear of the engine and was first run in 1946. The blades, however, were mostly unswept.[8] Other contra-rotating propeller engines that featured on common aircraft included the four powerful Kuznetsov NK-12 engines (each powering its own set of coaxial contra-rotating propellers) on the Soviet Union's Tupolev Tu-95 high-speed military bomber and Antonov An-22 military transport aircraft, and the Armstrong Siddeley Double Mamba (ASMD) engines (both connected to a lone set of coaxial contra-rotating propellers) on the British Fairey Gannet anti-submarine aircraft. Both setups had four largely unswept blades in the front propeller and the back propeller.

1970s–1980s

When the 1973 oil crisis caused petroleum price spikes in the early 1970s, interest in propfans soared, and NASA-funded research began to accelerate.[9] The propfan concept was outlined by Carl Rohrbach and Bruce Metzger of the Hamilton Standard division of United Technologies in 1975[10] and was patented by Rohrbach and Robert Cornell of Hamilton Standard in 1979.[1] Later work by General Electric on similar propulsors adopted the name unducted fan, which was a modified turbofan engine, with the fan placed outside the engine nacelle on the same axis as the compressor blades.

During this era, the propeller problems became fixable. Advances were made in structural materials, such as titanium metal and graphite and glass fiber composites infused with resin. These materials replaced aluminum and steel metals in blade construction, which allowed the blades to be made thinner and stronger.[11] Computer-aided design was also useful in refining blade characteristics. Since the blades bend and deflect with higher power loading and centrifugal force, the initial designs needed to be based on the in-motion shape. With the help of computers, the blade designers would then work backward to find the optimal unloaded shape for manufacturing purposes.[12]

Flight test programs

 
Ground–test installation of the Allison 501-M78 engine with an eight-bladed, 9.0 ft (2.7 m) diameter Hamilton Standard propeller for the NASA Propfan Test Assessment.

Hamilton Standard, the only large American manufacturer of aircraft propellers, developed the propfan concept in the early 1970s.[13] Hamilton Standard tested numerous variations in conjunction with NASA.[14][15]

Under the Propfan Test Assessment (PTA) program, Lockheed-Georgia proposed modifying a Gulfstream II to act as in-flight testbed for the propfan concept, while McDonnell Douglas proposed modifying a DC-9 for the same purpose.[16] NASA chose the Lockheed proposal. The Gulfstream II had a nacelle added to the left wing, containing a 6,000 horsepower (4,500 kilowatts) Allison 570 turboprop engine (derived from the XT701 turboshaft developed for the Boeing Vertol XCH-62 heavy lift helicopter). The engine used an eight-bladed, 9-foot diameter (2.7-metre; 110-inch; 270-centimetre), single-rotation Hamilton Standard SR-7 propfan. The test engine, which was named the Allison 501-M78,[17] had a thrust rating of 9,000 lbf (40 kN).[18] It was first operated in flight on March 28, 1987.[19] The extensive test program, which cost about $56 million,[20] racked up 73 flights and over 133 hours of flight time before finishing on March 25, 1988.[21] In 1989, however, the testbed aircraft returned to the air from April 3 through April 14 to measure ground noise levels during flight.[22][23] The engine was removed after that, and the aircraft was converted to a space shuttle training aircraft later that year.[24]

 
The GE36 on a McDonnell Douglas MD-80 demonstrator at the 1988 Farnborough Air Show. The gearless unducted fan engine had an overall diameter of 11.67 ft (3.56 m), with either eight or ten blades in front (depending on the particular configuration) and eight blades in back.

The GE36 Unducted Fan (UDF), from American engine maker General Electric (GE) with 35-percent participation from French partner Snecma (now Safran), was a variation on the original propfan concept and resembled a pusher configuration piston engine. GE's UDF had a novel direct-drive arrangement, where the reduction gearbox was replaced by a low-speed seven-stage free turbine. One set of turbine rotors drove the forward set of propellers, while the rear set was driven by the other set of rotors which rotated in the opposite direction. The turbine had 14 blade rows with seven stages. Each stage was a pair of contra-rotating rows.[25] Airframers, who had been wary of issue-prone gearboxes since the 1950s, liked GE's gearless version of the propfan:[12] Boeing intended to offer GE's pusher UDF engine on the 7J7 platform (which would have had a cruise speed of Mach 0.83),[26] and McDonnell Douglas planned to do likewise on their MD-94X airliner. The GE36 was first flight tested mounted on the #3 engine station of a Boeing 727-100 on August 20, 1986.[27] The GE36 UDF for the 7J7 was planned to have a thrust of 25,000 pounds-force (110 kN), but GE claimed that in general its UDF concept could cover a thrust range of 9,000 to 75,000 lbf (40 to 334 kN),[28] so a UDF engine could possibly match or surpass the thrust of the CF6, GE's family of widebody engines at that time.

McDonnell Douglas developed a proof-of-concept aircraft by modifying its company-owned MD-80, which is suited for propfans due to its aft fuselage-mounted engines (like its DC-9 ancestor), in preparation for the possible propfan-powered MD-91 and MD-92 derivatives and a possible MD-94X clean-sheet aircraft. They replaced the left side JT8D turbofan engine with the GE36. Test flights began in May 1987,[29] which proved the design's airworthiness, aerodynamic characteristics, and noise signature. Following the initial tests, a first-class cabin was installed inside the aft fuselage and airline executives were offered the opportunity to experience the UDF-powered aircraft first-hand. The test and marketing flights of the GE-outfitted demonstrator aircraft concluded in 1988, exhibiting a 30% reduction in fuel consumption over turbo-fan powered MD-80, full Stage 3 noise compliance, and low levels of interior noise/vibration. The GE36 would have the same 25,000 lbf (110 kN) thrust on the MD-92X, but the same engine would be derated to 22,000 lbf (98 kN) thrust for the smaller MD-91X. The MD-80 was also successfully flight tested in April 1989 with the 578-DX propfan, which was a prototype from the Allison Engine Company (at that time a division of General Motors) that was also derived from the Allison XT701 and built with Hamilton Standard propellers. The engine program was jointly developed between Allison and another division of United Technologies, the engine maker Pratt & Whitney. Unlike the competing GE36 UDF, the 578-DX was fairly conventional, having a reduction gearbox between the LP turbine and the propfan blades. Due to jet fuel price drops and shifting marketing priorities, Douglas shelved the propfan program later that year.

 
The PW–Allison 578-DX engine installed on the same MD-80 testbed. The contra-rotating, geared propfan engine is 11.6 ft (3.5 m) in diameter, with six blades in front and six blades in back.

Other proposed applications

Other announcements of future propfan-powered airliners included:

  • The Fokker FXX, a 100-120 seat propfan-powered aircraft that was studied in 1982[30]
  • The MPC-75, an 80-seat, Mach 0.76 cruise speed, 1,500 nmi range (1,700 mi; 2,800 km) regional aircraft conceived by Messerschmitt-Bölkow-Blohm (MBB) of West Germany and the Chinese Aero Technology Export/Import Corporation (CATIC); used as the baseline powerplant two direct-drive General Electric GE38-B5 UDF engines delivering 9,644 and 2,190 lbf (4,374 and 993 kgf; 42.90 and 9.74 kN) in static thrust and cruise with a thrust-specific fuel consumption (TSFC) of 0.240 and 0.519 lb/(lbf⋅h) (6.8 and 14.7 g/(kN⋅s)), respectively, through an 85 in (2.1 m) diameter propfan with 11 and 9 blades on the contra-rotating propellers; proposed as an alternative powerplant the 14,500 lbf (6,600 kgf; 64 kN) static thrust, PW–Allison 501-M80E geared propfan engine, which was derived from the 501-M80C turboshaft that was chosen to power the United States Navy's Osprey tiltrotor aircraft;[31] later described the propfan engine as one with the core from the T406 (the military designation for the Osprey's powerplant), containing a 108 in diameter (2.7 m) propfan that provided 2,450 lbf (1,110 kgf; 10.9 kN) of thrust in cruise with a TSFC of 0.51 lb/(lbf⋅h) (14 g/(kN⋅s))[32]: 1090 
  • The ATR 92, a 400 kn cruising speed (460 mph; 740 km/h), five- or six-abreast, 100-seat aircraft from Avions de Transport Regional (ATR, a joint venture between France's Aerospatiale and Italy's Aeritalia)[33] and Spain's Construcciones Aeronáuticas SA (CASA),[34] which would possibly be powered by the UDF[35]
  • The Aerospatiale AS.100, a regional aircraft with a range of 1,500 nmi (1,700 mi; 2,800 km), a cruise speed of Mach 0.74–0.78 at 30,000 ft (9,100 m) altitude,[36] and a capacity of 80-100 seats, that might be powered by the UDF[35] or by a propfan version of the Allison T406[34] tiltrotor engine
  • The ATRA-90 (Advanced Technology Regional Aircraft), an 83– to 115–seat aircraft with a range of 1,500–2,100 nmi (1,700–2,400 mi; 2,800–3,900 km) and a cruise speed of Mach 0.8 at 30,000 ft (9,100 m) altitude, that was to be built by a multinational joint venture consisting of Industri Pesawat Terbang Nusantara (IPTN) of Indonesia, Boeing (USA), MBB (West Germany), and Fokker (Netherlands)[36]
  • The Tupolev Tu-334, a 126-seat aircraft that can travel 1,860 nmi (2,140 mi; 3,450 km) with 11,430 kg payload (25,200 lb; 11.43 t; 12.60-short-ton), which is powered by two Progress (also known as Lotarev) D-236 propfans[37] with a specific fuel burn of 0.46 kg/kg-thrust/hour, a cruise thrust of 1.6 tonnes-force (3,500 lbf; 16 kN), and a static thrust of 8 to 9 tf (18,000 to 20,000 lbf; 78 to 88 kN)[38]
  • The Ilyushin Il-88, a successor to the four-turboprop Antonov An-12 tactical transporter that would be powered by two 11,000 hp (8,200 kW) Progress D-236 propfans[39]
  • The Ilyushin Il-118, an upgrade to the four-turboprop Ilyushin Il-18 airliner;[40] proposed in 1984, the aircraft would instead be powered by two D-236 propfans, with the eight-bladed front propeller on each engine rotating at a speed of 1,100 rpm and the six-bladed back propeller turning at 1,000 rpm to lower noise and vibration[41]
  • A re-engined Antonov An-124, replacing the four Progress D-18T turbofans by 55,100 lbf thrust (245.2 kN) Kuznetsov NK-62 propfans[42]

Decline

None of these projects came to fruition, however, mainly because of excessive cabin noise (compared to turbofans) and low fuel prices.[43] For General Electric, the GE36 UDF was meant to replace the CFM56 high-bypass turbofan that it produced with equal partner Snecma in their CFM International joint venture. In the 1980s the engine was initially uncompetitive against the International Aero Engines rival offering, the IAE V2500. In December 1986, the chairman of Snecma declared that the in-development CFM56-5S2 would be the last turbofan created for the CFM56 family, and that "There is no point in spending more money on turbofans. UDF is the future."[44] The V2500 ran into technical problems in 1987, however, and the CFM56 gained major sales momentum. General Electric lost interest in having the GE36 cannibalize the CFM56, which went five years before it received its first order in 1979, and while "the UDF could be made reliable by earlier standards, turbofans were getting much, much better than that." General Electric added the UDF's blade technology directly into the GE90, the most powerful jet engine ever produced, for the Boeing 777.[45]

1990s

 
The Progress D-236 propfan engine on the Yak-42E-LL testbed aircraft at the Paris Air Show in 1991.

At the beginning of the 1990s, the Soviet Union/Russia performed flight tests on the Progress D-236, a geared contra-rotating propfan engine based on the core of the Progress D-36 turbofan, with eight blades on the front propeller and six blades on the back propeller. One testbed was a 10,100 hp (7,500 kW) propfan mounted to an Ilyushin Il-76 and flown to the Hannover ILA 90 airshow, which was intended for an unidentified four-propfan aircraft.[46] The D-236 flew 36 times for a total of 70 flight test hours on the Il-76.[47] The other testbed was a 10,990 hp (8,195 kW), 14 ft unit (4.2 m; 170 in; 420 cm) mounted to a Yakovlev Yak-42E-LL and flown to the 1991 Paris Air Show, as a demonstration for the planned Yak-46 aircraft with twin propfan engines,[48] which in its base 150-seat version would have a range of 1,900 nmi (2,200 mi; 3,500 km) and cruise at a speed of 460 kn (530 mph; 850 km/h; 780 ft/s; 240 m/s)[49] (Mach 0.75).[50] The Soviets claimed the D-236 had a true aerodynamic efficiency of 28 percent and a fuel savings of 30 percent over an equivalent turboprop. They also revealed plans for propfans with power ratings of 14,100 and 30,200 hp (10,500 and 22,500 kW).[46]

 
Progress D27 Propfans fitted to an Antonov An-70.

Like the Progress D-236, the more powerful Progress D-27 propfan engine is a contra-rotating propfan with eight front blades and six back blades,[50] but the D-27 has advanced composite blades with a reduced thickness-to-chord ratio and a more pronounced curvature at the leading edge.[51] An engine that was launched in 1985, the D-27[52] delivers 14,000 hp (10,440 kW) of power with 27,000 lbf (119 kN) of thrust at takeoff.[53] Two rear-mounted D-27 propfans propelled the Ukrainian Antonov An-180, which was scheduled for a 1995 first flight and a 1997 entry into service.[54] In January 1994, Antonov rolled out the first prototype of the An-70 military transport aircraft, powered by four Progress D-27s attached to wings mounted to the top of the fuselage.[53] The Russian Air Force placed an order for 164 aircraft in 2003, later canceled. As of 2013, the An-70 was still thought to have a promising future as a freighter.[55] However, since the propeller component of the Progress D-27 is made by Russia's SPE Aerosila, the An-70 was stymied by Ukraine's political conflict with Russia. Instead, Antonov began working with Turkey in 2018 to redevelop the An-70 as a rebranded An-77, so that the aircraft can comply with modern-day requirements without Russian supplier participation.[56]

Twenty-first century

In the first decade of the 21st century, rising jet fuel prices increased emphasis on engine/airframe efficiency to reduce emissions, which renewed interest in the propfan concept for jetliners beyond the Boeing 787 and Airbus A350XWB. For instance, Airbus patented aircraft designs with twin rear-mounted contra-rotating propfans.[57] Rolls-Royce had the rear (pusher) configured RB.509-11 and front (tractor) configured RB.509-14 geared propfan designs, which produced 15,000–25,000 lbf thrust (6,800–11,300 kgf; 67–111 kN) using the gas generator from its XG-40 engine[58] with 13,000 hp (9,700 kW) of shaft power.[59] It became lukewarm on propfan technology in the 1980s[60]although it developed an open rotor design that was thought to be a finalist for the Irkut MS-21 narrowbody aircraft.[61] The Rolls-Royce RB3011 engine would have a diameter of about 170 in (430 cm; 14 ft; 4.3 m) and require a 16,000 shaft hp (12,000 kW) gearbox.[62]

 
Safran open rotor mockup in 2017.

The European Commission launched an Open Rotor demonstration in 2008 led by Safran within the Clean Sky program funded with 65 million euros over eight years. A demonstrator was assembled in 2015, and ground tested in May 2017 on its open-air test rig in Istres, aiming to reduce fuel consumption and associated CO2 emissions by 30% compared with current CFM56 turbofans.[63] After the completion of ground testing at the end of 2017, Safran's geared open rotor engine had reached technology readiness level 5.[64] The demonstrator's twelve-blade front propeller and ten-blade back propeller had diameters of 13.1 and 12.5 ft (4.0 and 3.8 m; 160 and 150 in; 400 and 380 cm), respectively. The demonstrator, based on the core of the Snecma M88 military fighter engine, uses up to 12,200 horsepower (9 megawatts), provides a thrust of about 22,000 lbf (100 kN), and would cruise at a speed of Mach 0.75.[65] Safran's future open rotor engine, however, would have a maximum diameter of almost 14.8 ft (4.50 m; 177 in; 450 cm).[66]

In 2007, the Progress D-27 was successfully modified to meet the United States Federal Aviation Administration (FAA) Stage 4 regulations, which correspond to International Civil Aviation Organization (ICAO) Chapter 4 standards.[67] A 2012 trade study projected that propfan noise would be 10–13 decibels quieter than allowed by Stage 4 regulations.[68] Stage 5 noise limits reduce the limits by only seven effective perceived noise decibels (EPNdB),[69] within the propfan noise envelope. The study also projected that open rotors would be nine percent more fuel-efficient but remain 10–12 decibels louder than turbofans.[68] Snecma claimed that its propfan engines would have about the same noise levels as its CFM LEAP turbofan engine.[70]

In 2021, CFM announced its Revolutionary Innovation for Sustainable Engines (RISE) development program to produce a single-stage, gear-driven propfan paired with active stators in a puller/tractor, configuration with flight tests to begin by 2025. The rotor was expected to be 12–13 ft (3.7–4.0 m) in diameter. The engine was expected to produce 20,000–35,000 lbf (9,100–15,900 kgf; 89–156 kN) of thrust, with a 20% increase in fuel efficiency. The company claimed its motivation was the global emphasis on reducing emissions. The engine was planned to support both hydrogen and sustainable aviation fuels. The engine was expected to include a compact high-pressure core and a recuperating system to preheat combustion air with exhaust heat along with ceramic matrix composites in the hot section and resin-transfer-molded composite fan blades. In addition to the rotor, the design includes a nonrotating set of variable-pitch stator blades that act as flow recovery vanes. The design increases the fan-pressure ratio and reduces rotor loading, increasing airspeed. The fan stage is to be powered by a high-speed booster compressor and a high-speed, low-pressure-shaft-driven front gearbox. The engine is slated for certification as an "integrated engine" instead of a traditional "propeller/engine" because of its airframe integration complexity.[71] CFM planned for an aerodynamically three-dimensional rotor with 12 woven carbon-fiber composite blades. Aided by a smaller engine core, the CFM RISE engine would have a bypass ratio of 75.[72]

Challenges

Blade design

Turboprops have an optimum speed below about 450 mph (390 kn; 720 km/h),[73] because propellers lose efficiency at high speed, due to an effect known as wave drag that occurs just below supersonic speeds. This powerful drag has a sudden onset, and it led to the concept of a sound barrier when first encountered in the 1940s. This effect can happen whenever the propeller is spun fast enough that the blade tips approach the speed of sound.

The most effective way to address this problem is by adding blades to the propeller, allowing it to deliver more power at a lower rotational speed. This is why many World War II fighter designs started with two or three-blade propellers but by the end of the war were using up to five blades; as the engines were upgraded, new propellers were needed to more efficiently convert that power. Adding blades makes the propeller harder to balance and maintain, and the additional blades cause minor performance penalties due to drag and efficiency issues. But even with these sorts of measures, eventually the forward speed of the plane combined with the rotational speed of the propeller blade tips (together known as the helical tip speed) will again result in wave drag problems. For most aircraft, this will occur at speeds over about 450 mph (390 kn; 720 km/h).

 
Swept propeller

A method of decreasing wave drag was discovered by German researchers in 1935—sweeping the wing backwards. Today, almost all aircraft designed to fly much above 450 mph (390 kn; 720 km/h) use a swept wing. Since the inside of the propeller is moving slower in the rotational direction than the outside, the blade is progressively more swept back toward the outside, leading to a curved shape similar to a scimitar - a practice that was first used as far back as 1909, in the Chauvière two-bladed wood propeller used on the Blériot XI. (At the blade root, the blade is actually swept forward into the rotational direction, to counter the twisting that is generated by the backward swept blade tips.)[74] The Hamilton Standard test propfan was swept progressively to a 39-degree maximum at the blade tips, allowing the propfan to produce thrust even though the blades had a helical tip speed of about Mach 1.15.[75]

The blades of the GE36 UDF and the 578-DX have a maximum tip speed in rotation of about 750–800 ft/s (230–240 m/s; 510–550 mph; 820–880 km/h),[76] or about half the maximum tip speed for the propeller blades of a conventional turbofan.[77] That maximum blade tip speed would be kept constant despite wider or narrower propeller diameter (resulting in an RPM reduction or increase, respectively).[3]

Drag can also be reduced by making the blades thinner, which increases the speed that the blades can attain before the air ahead of them becomes compressible and causes shock waves. For example, the blades of the Hamilton Standard test propfan had a thickness-to-chord ratio that tapered from less than 20% at the spinner junction to 2% at the tips, and 4% at mid-span.[75] Propfan blades had approximately half the thickness-to-chord ratio of the best conventional propeller blades of the era,[78] thinned to razor-like sharpness at their edges,[12][79] and weighed as little as 20 pounds (9.1 kg).[80] (The GE36 UDF engine that was tested on the Boeing 727 had front and back blades that weighed 22.5 and 21.5 lb (10.2 and 9.8 kg) each.)[81]

 
A comparison of the propfan with other types of aircraft engines.

Noise

One of the major problems with the propfan is noise. The propfan research in the 1980s discovered ways to reduce noise, but at the cost of reduced fuel efficiency, mitigating some of the advantages of a propfan.

General methods for reducing noise include lowering tip speeds and decreasing blade loading, or the amount of thrust per unit of blade surface area. A concept similar to wing loading, blade loading can be reduced by lowering the thrust requirement or by increasing the amount, width, and/or length of the blades. For contra-rotating propfans, which can be louder than turboprops or single-rotating propfans, noise can also be lowered by:[82]

  • increasing the gap between the propellers;
  • keeping back propeller blade lengths shorter than those of the front propeller, so that the back propeller blades avoid cutting through the blade tip vortices of the front propeller (blade-vortex interaction);
  • using different numbers of blades on the two propellers, to avoid acoustic reinforcement; and
  • turning the front propeller and back propeller at different speeds, also to prevent acoustic reinforcement.[41]

Community noise

Engine makers expect propfan implementations to meet community (as opposed to cabin) noise regulations without sacrificing the efficiency advantage. Some think that propfans can potentially cause less of a community impact than turbofans, given their lower rotational speeds. Geared propfans should have an advantage over ungeared propfans for the same reason.[83]

In 2007, the Progress D-27 was successfully modified to meet the United States Federal Aviation Administration (FAA) Stage 4 regulations, which correspond to International Civil Aviation Organization (ICAO) Chapter 4 standards and were adopted in 2006.[67] A 2012 trade study projected that noise from existing open rotor technology would be 10–13 decibels quieter than the maximum noise level allowed by the Stage 4 regulations;[68] the newer Stage 5 noise limits (which replaced the Stage 4 regulations for larger aircraft in 2018 and mirrored the ICAO Chapter 14 noise standard established in 2014) are more restrictive than the Stage 4 requirement by only seven effective perceived noise decibels (EPNdB),[69] so current propfan technology shouldn't be hindered by the Stage 5 standards. The study also projected that at existing technology levels, open rotors would be nine percent more fuel-efficient but remain 10–12 decibels louder than turbofans.[68] Snecma, however, maintains that open-rotor tests show that its propfan engines would have about the same noise levels as its CFM LEAP turbofan engine,[70] which entered service in 2016.

Further reductions can be achieved by redesigning the aircraft structure to shield noise from the ground. For example, another study estimated that if propfan engines were used to power a hybrid wing body aircraft instead of a conventional tube-and-wing aircraft, noise levels could be reduced by as much as 38 EPNdB compared to ICAO Chapter 4 requirements.[84] In 2007, the British budget airline easyJet introduced its ecoJet concept, a 150-250 seat aircraft with V-mounted open rotor engines joined to the rear fuselage and shielded by a U-tail.[85] It unsuccessfully initiated discussions with Airbus, Boeing, and Rolls-Royce to produce the aircraft.[86]

Size

A twin-engine aircraft carrying 100–150 passengers would require propfan diameters of 120–168 inches (300–430 cm; 10.0–14.0 ft; 3.0–4.3 m),[75] and a propfan with a propeller diameter of 236 in (600 cm; 19.7 ft; 6.0 m) would theoretically produce almost 60,000 lbf (270 kN) of thrust.[87] These sizes achieve the desired high bypass ratios of over 30, but they are approximately twice the diameter of turbofan engines of equivalent capability.[65] For this reason, airframers usually design the empennage with a T-tail configuration for aerodynamic purposes, and the propfans may be attached to the upper part of the rear fuselage. For the Rolls-Royce RB3011 propfan prototype, a pylon of about 8.3 ft (2.54 m; 100 in; 254 cm) long would be required to connect the center of each engine to the side of the fuselage.[88] If the propfans are mounted to the wings, the wings would be attached to the aircraft in a high wing configuration, which allows for ground clearance without requiring excessively long landing gear. For the same amount of power or thrust produced, an unducted fan requires shorter blades than a geared propfan,[89] although the overall installation issues still apply.

Output rating

Turboprops and most propfans are rated by the amount of shaft horsepower (shp) that they produce, as opposed to turbofans and the UDF propfan type, which are rated by the amount of thrust they put out. The rule of thumb is that at sea level with a static engine, 1 shaft horsepower (750 watts) is roughly equivalent of 2 pounds-force (8.9 N) thrust, but at cruise altitude, that changes to about 1 pound-force (4.4 N) thrust. That means two 25,000 lbf thrust (110 kN) engines can theoretically be replaced with a pair of 12,000–13,000 shaft hp (8,900–9,700 kW) propfans or with two 25,000 lbf thrust (110 kN) UDF propfans.[3]

Aircraft with propfans

Main category: Propfan-powered aircraft

Proposed aircraft with propfans

See also

Comparable engines

Related lists

References

  1. ^ a b US 4171183, Cornell, Robert W. & Rohrbach, Carl, "Multi-bladed, high speed prop-fan", published 16 Oct 1979, assigned to United Technologies Corporation 
  2. ^ "What is propfan?". Flight International. January 16, 1982. p. 113. ISSN 0015-3710.
  3. ^ a b c "Propfan/UDF: some answers questioned". Paris Review. Flight International. June 15, 1985. pp. 8–9. Retrieved March 28, 2019.
  4. ^ "Propfans—'the genie is out of the bottle'" (PDF). Air Transport. Flight International. Vol. 129, no. 3999. New Delhi, India. February 22, 1986. p. 8. Retrieved May 17, 2019.
  5. ^ EASA 2015, pp. 5–6.
  6. ^ El-Sayed, Ahmed F. (July 6, 2017). Aircraft propulsion and gas turbine engines (2nd ed.). CRC Press. Table 6.11. ISBN 9781466595187. OCLC 986784025.
  7. ^ Kuntz et al., pp. 2 to 3.
  8. ^ "Metrovick F.5: Open-fan thrust augmenter on standard F.2 gas generator". Flight. January 2, 1947. p. 18. (PDF) from the original on November 7, 2017. Retrieved March 28, 2019.
  9. ^ Kuntz et al., p. 3.
  10. ^ Rohrbach, C.; Metzger, F. B. (September 29 – October 1, 1975). The Prop-Fan - A new look in propulsors. 11th Propulsion Conference. Vol. 75–1208. Anaheim, California: American Institute of Aeronautics and Astronautics (AIAA) and Society of Automotive Engineers (SAE). doi:10.2514/6.1975-1208.
  11. ^ Ferrell, J. E. (October 12, 1986). "Propfan gets another whirl". San Francisco Examiner. Retrieved April 25, 2019 – via Chicago Tribune.
  12. ^ a b c Schefter, Jim (March 1985). "So long, jets? Ingenious new blades make propliners as fast as jets". Cover story. Popular Science. Vol. 226, no. 3. pp. 66–69. ISSN 0161-7370.
  13. ^ Wilford, John Noble (August 24, 1982). "Sleek, high-performance designs give propellers a future after all". Science Times. New York Times. Edwards Air Force Base, California, USA. p. C1. ISSN 0362-4331.
  14. ^ Rohrbach, Carl (July 26–29, 1976). A report on the aerodynamic design and wind tunnel test of a Prop-Fan model. 12th Propulsion Conference. Vol. 76–667. Palo Alto, California: American Institute of Aeronautics and Astronautics (AIAA) and Society of Automotive Engineers (SAE). doi:10.2514/6.1976-667.
  15. ^ Jeracki, Robert J.; Mikkelson, Daniel C.; Blaha, Bernard J. (April 3–6, 1979). Wind tunnel performance of four energy efficient propellers designed for Mach 0.8 cruise. SAE Business Aircraft Meeting and Exposition. Vol. 790573. Wichita, Kansas: Society of Automotive Engineers (SAE). doi:10.4271/790573. hdl:2060/19790011898. OCLC 37181399.
  16. ^ Goldsmith 1981.
  17. ^ "Propfanned G2 takes to the air" (PDF). World News. Flight International. Vol. 131, no. 4061. Marietta, Georgia, USA. May 9, 1987. p. 2. ISSN 0015-3710.
  18. ^ Hager & Vrabel 1988, p. 56.
  19. ^ "Gulfstream flies with propfan" (PDF). Propulsion. Flight International. Vol. 131, no. 4062. May 16, 1987. p. 16. ISSN 0015-3710.
  20. ^ "Propfan acoustic tests completed" (PDF). Flight International. Vol. 133, no. 4114. May 21, 1988. p. 37. ISSN 0015-3710.
  21. ^ Poland, D. T.; Bartel, H. W.; Brown, P. C. (July 11–13, 1988). PTA flight test overview. Joint Propulsion Conference (24th ed.). Boston, Massachusetts, USA. doi:10.2514/6.1988-2803. OCLC 1109689683.
  22. ^ Rickley, E.J. (September 1989). En route noise: NASA propfan test aircraft (calculated source noise) (Report). Washington, D.C.: U.S. Department of Transportation (DOT) Federal Aviation Administration (FAA) Office of Environment. pp. 41–59. alternate url
  23. ^ Garber, Donald P.; Willshire, William L. Jr. (September 1994). En route noise levels from Propfan Test Assessment airplane (Report). Hampton, Virginia: National Aeronautics and Space Administration (NASA). alternate url
  24. ^ "NASA shuttle training aircraft". Texas Air & Space Museum. Retrieved July 18, 2019.
  25. ^ GE Aircraft Engines 1987.
  26. ^ "Manufacturers positioning for coming competitive battles". Air Transport World. No. September 1986. Farnborough, England, United Kingdom. pp. 20+. ISSN 0002-2543. 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.
  27. ^ "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.
  28. ^ "Propfans ready by 1990". Paris Report. Flight International. June 8, 1985. p. 5. (PDF) from the original on September 25, 2014. Retrieved March 28, 2019.
  29. ^ Warwick, Graham (August 15, 1987). "UHB: the acid test". Flight International. pp. 22–23. Retrieved March 22, 2019.
  30. ^ "Delta demands 150-seater as MDF-100 dies" (PDF). Air transport. Flight International. Vol. 121, no. 3798. February 20, 1982. p. 404. ISSN 0015-3710.
  31. ^ MBB CATIC Association (July 1987). MPC 75 feasibility study — summary report: B1 - project definition (PDF) (Report).
  32. ^ Fischer, B.; Chen, J.Z. (September 20–25, 1992). MPC75 - The evolution of a new regional airliner for the late nineties (PDF). Congress of the International Council of the Aeronautical Sciences (18th ed.). Beijing, People's Republic of China. pp. 1084–1093. OCLC 761191715.
  33. ^ "ATR plans 100-seater" (PDF). Farnborough First News. Flight International. Farnborough, England, United Kingdom. September 10, 1988. p. 16. ISSN 0015-3710.
  34. ^ a b Sedbon, Gilbert (December 17, 1988). "Spain joins 'ATR 92' study" (PDF). Flight International. Paris, France. p. 14. ISSN 0015-3710.
  35. ^ a b "Snecma raises propfan funds". Air Transport. Flight International. Vol. 132, no. 4086. Paris, France. October 31, 1987. p. 6. ISSN 0015-3710.
  36. ^ a b (PDF). Developments. Science and Technology Perspectives. Vol. 2, no. 12. Foreign Broadcast Information Service (published August 21, 1987). Air and Cosmos. June 20, 1987. p. 2. OCLC 13857080. Archived from the original (PDF) on January 23, 2017.
  37. ^ "TU-134 replacement decision due". Moscow Aerospace '90. Flight International. Vol. 138, no. 4237. October 10–16, 1990. p. 28. ISSN 0015-3710.
  38. ^ Postlethwaite, Alan (April 29, 1989). "Tupolev unveils propfan airliner". Flight International. Vol. 135, no. 4162. Moscow, Soviet Union. p. 10. ISSN 0015-3710.
  39. ^ "Ilyushin Il-276 (SVTS)". Ruslet: Great Encyclopedia of Russian and Chinese Aviation (in Russian). Retrieved April 23, 2019.
  40. ^ "Ilyushin IL-18 (Coot): Turboprop-powered passenger airliner / maritime reconnaissance platform". from the original on March 9, 2019. Retrieved April 23, 2019.
  41. ^ a b Gordon, Yefim; Komissarov, Dmitriy (2003). Ilyushin IL-18/-20/-22: A versatile turboprop transport. Aerofax. p. 47. ISBN 9781857801576. OCLC 52195311.
  42. ^ "NK-62, NK-63 - Kuznetsov, USSR" (in Czech).
  43. ^ Flight International (2007-07-12). "Whatever happened to propfans?". from the original on October 20, 2007. Retrieved January 28, 2019.
  44. ^ "France backs UDF". Propulsion. Flight International. Vol. 130, no. 4042. Villaroche, France. December 20, 1986. p. 63. ISSN 0015-3710.
  45. ^ 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. Vol. 20, no. 3. pp. 42–49. ISSN 0886-2257. OCLC 109549426. from the original on August 14, 2017. Retrieved January 28, 2019.
  46. ^ a b "Soviets show Il-76 mounted 'propfan'". Flight International. Vol. 137, no. 4217. May 23–29, 1990. p. 9. ISSN 0015-3710.
  47. ^ Komissarov, Dmitriy; Gordon, Yefim (2001). Ilyushin IL-76: Russia's versatile airlifter. Aerofax. pp. 43–45. ISBN 9781857801064. OCLC 47676935.
  48. ^ "Yak propfan pops into Paris". Paris Show Report. Flight International. Vol. 140, no. 4272. June 26 – July 2, 1991. p. 16. ISSN 0015-3710.
  49. ^ Rybak, Boris (May 22–28, 1991). "Yakovlev takes propfan lead: While development of fuel-saving propfan engines languishes in the West, work continues in the Soviet Union where recent fuel shortages have underscored the need for new engine technology". Commercial Engines. Flight International. Vol. 139, no. 4267. pp. 27–28. ISSN 0015-3710.
  50. ^ a b Postlethwaite, Alan (May 9–15, 1990). "Yakovlev strikes back: Propfan and other high-technology derivatives of the Yak-42 airliner (NATO codename Clobber) are planned". Flight International. Vol. 137, no. 4215. pp. 61–62, 65–66. ISSN 0015-3710.
  51. ^ "More detailed information about D-27 engine". SE Ivchenko-Progress. Archived from the original on 2013-01-26. Retrieved 2012-06-29.
  52. ^ Dmytriyev, Sergiy (October 12–14, 2015). Ivchenko-Progress innovations for turboprop engines (PDF). 5th Symposium on Collaboration in Aircraft Design. Naples, Italy. (PDF) from the original on April 19, 2019.
  53. ^ a b Velovich, Alexander (February 9–15, 1994). "Against all odds: Despite having to toil in a cold economic climate, Antonov has rolled out the first of what it hopes will be many of its An-70 four-engine transport aircraft". Antonov An-70. Flight International. Vol. 145, no. 4407. pp. 34–35. ISSN 0015-3710.
  54. ^ "An-180 project by ANTK O.K.Antonov".
  55. ^ "Freighter of the future?". Air Cargo World. February 15, 2013.
  56. ^ (PDF). Civil News. Scramble. No. 471. Dutch Aviation Society. August 2018. p. 38. Archived from the original (PDF) on May 2, 2019.
  57. ^ US application 2009020643, Airbus & Christophe Cros, "Aircraft having reduced environmental impact", published 2009-01-22 
  58. ^ Alekseyev, Col. Yu. (1988). "Propfan engines". Zarubezhnoye Voyennoye Obozreniye. Moscow: Soviet Union Ministry of Defense (published March 21, 1989) (10): 27–29. OCLC 946659244 – via Soviet Union Foreign Military Review.
  59. ^ . Archived from the original on March 5, 2013. Retrieved April 30, 2019.
  60. ^ Colchester, Nicholas (March 24, 1986). "Elegance is key to cut and thrust". Technology. Financial Times. p. 12.
  61. ^ Karnozov, Vladimir (September 3, 2008). "Yakovlev ready to call for MS-21 systems tenders as design freeze nears". Flight International. Moscow, Russia.
  62. ^ Butterworth-Hayes, Philip (March 2010). (PDF). Aerospace America. Vol. 48, no. 3. pp. 38–42. ISSN 0740-722X. OCLC 664005753. Archived from the original (PDF) on April 2, 2015.
  63. ^ "Safran celebrates successful start of Open Rotor demonstrator tests on new open-air test rig in southern France" (Press release). Safran. October 3, 2017. from the original on August 29, 2018. Retrieved October 3, 2017.
  64. ^ Angrand, Antony (May 10, 2019). "Safran ponders open rotor options". Air & Cosmos International. No. 7. pp. 22–23. ISSN 1240-3113 – via Issuu.
  65. ^ a b Ebner, Ulrike (February 14, 2018). "Treibstoff-sparwunder: Open rotor". Flug Revue (in German). from the original on March 29, 2019.
  66. ^ Cueille, Stéphane (March 25, 2019). "What does the future hold in store for the Open Rotor?". from the original on March 29, 2019. Retrieved March 29, 2019 – via Safran.
  67. ^ a b Karnozov, Vladimir (May 1, 2007). "Military engines: Development thrusts". Flight International. Moscow, Russia. ISSN 0015-3710. from the original on April 2, 2016.
  68. ^ a b c d Croft, John (July 5, 2012). "Open rotor noise not a barrier to entry: GE". Flight International. from the original on July 18, 2012. Retrieved July 21, 2012.
  69. ^ a b Spencer, Jessica C. (October 25, 2017). "Stage 5 aircraft noise standards approved in US – what does it mean for airports?". from the original on March 28, 2019. Retrieved March 28, 2019.
  70. ^ a b Eshel, Tamir (January 2, 2014). "Snecma tests open rotor engine". Defense Update. from the original on July 3, 2017. Retrieved April 10, 2019.
  71. ^ Norris, Guy; Dubois, Thierry (June 25, 2021). . Aviation Week. Archived from the original on 2021-07-09. Retrieved 2021-06-30.
  72. ^ Kjelgaard, Chris (November 10, 2021). "Commercial-engine OEMs detail emissions work". Dubai Airshow. AINonline.
  73. ^ Spakovszky, Zoltan (2009). "Unified propulsion lecture 1". Unified Engineering Lecture Notes. MIT. from the original on March 31, 2018. Retrieved 2009-04-03.
  74. ^ Garrison, Peter (February 1990). "Props and circumstance". Technicalities. Flying. Vol. 117, no. 2.
  75. ^ a b c Hammitt, Tom (June 1985). "Ace of blades: Their radical shapes hiding a conservative streak, propfans could combine fanjet speed with propeller efficiency". Flying. Vol. 112, no. 6. pp. 66–68, 70. Retrieved March 28, 2019.
  76. ^ "Date set for Allison UHB flight test". Propulsion. Flight International. Long Beach, California, USA. February 8, 1986. pp. 50–51. from the original on March 27, 2019. Retrieved March 28, 2019.
  77. ^ "The fans are flying". Farnborough Report. Flight International. September 13, 1986. pp. 18, 20. Retrieved March 25, 2019.
  78. ^ Hager & Vrabel 1988, p. 6.
  79. ^ Nesbitt, Jim (September 22, 1985). "Jet engines propel into new era". Orlando Sentinel. Marietta, Georgia, USA. from the original on March 30, 2019. Retrieved March 29, 2019.
  80. ^ Moll, Nigel (May 1987). "7J7: The next new Boeing". Flying. pp. 37, 39.
  81. ^ GE Aircraft Engines 1987, p. 163.
  82. ^ Hager & Vrabel 1988, p. 82.
  83. ^ Warwick, Graham; Moxon, Julian (May 23, 1987). "The power of persuasion". Flight International. Washington, DC, USA. pp. 39–41.
  84. ^ Trimble, Stephen (February 12, 2014). "Analysis: Noise goals in sight for open-rotor researchers". News. Flight International. Washington, D. C., USA. p. 28. ISSN 0015-3710.
  85. ^ . easyJet airline company ltd. Archived from the original on June 16, 2007. Retrieved December 30, 2017.
  86. ^ Robinson, Tim (October 6, 2017). "Can easyJet short circuit electric airliner flight?". Royal Aeronautical Society.
  87. ^ Learmount, David (August 30, 1986). "US air transport technology: where next?". Flight International. pp. 120–122, 124, 128. Retrieved March 28, 2019.
  88. ^ Doyle, Andrew (October 5, 2009). "Keeping options open". Flight International. London, England, United Kingdom.
  89. ^ 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 Geographic Information Systems (GIS) Team.

General resources

  • Prop fan propulsion concepts: Technology Review, Design Methodology, State-of-the-art designs and future outlook. Raymond Scott Ciszek. University of Virginia Department of Mechanical and Aerospace Engineering. Senior Thesis Project. March 25, 2002

Bibliography

  • Dubois, Thierry; Warwick, Graham (January 9–22, 2017). "Last of the CRORs: Safran is about to test a counter-rotating open rotor engine, despite waning appeal". Advanced Propulsion. Aviation Week & Space Technology. Vol. 179, no. 1. Lyon, France and Washington, D.C., USA. p. 54. OCLC 969306167.
  • Kinney, Jeremy R. (2017). "4: The Quest for Propulsive Efficiency, 1976–1989" (PDF). The power for flight: NASA's contributions to aircraft propulsion. NASA aeronautics book series. Vol. 631. pp. 114–125. hdl:2060/20180003207. ISBN 9781626830370. OCLC 990183146. alternate url
  • Notice of proposed amendment (NPA) 2015-22: Open rotor engine and installation (PDF), European Aviation Safety Agency, December 21, 2015, (PDF) from the original on August 25, 2018, retrieved March 28, 2019
  • 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. (PDF) from the original on 8 July 2018. Retrieved 8 July 2018.
  • Coniglio, Sergio (February 2010). "Military aircraft propulsion: Jets vs. props". Military Technology (MILTECH). Vol. 34, no. 2. Mönch Publishing Group. pp. 77–84. ISSN 0722-3226. OCLC 527912380.
  • Bowles, Mark (2010). "Advanced turboprops and laminar flow" (PDF). The Apollo of aeronautics: NASA's aircraft energy efficiency program, 1973-1987. NASA-SP. Vol. 2009–574. Washington, D.C.: National Aeronautics and Space Administration. pp. 122–136. hdl:2060/20110011568. ISBN 9780160842955. OCLC 465190382. Retrieved 25 September 2018. alternate url
  • Doyle, Andrew (October 6, 2009). "Open rotor: how does it work?". Flight International. London, England, UK. ISSN 0015-3710.
  • Turner, Aimée (March 23, 2009). "Back to the windtunnel". Flight International. London, England, United Kingdom.
  • "EU explores cleaner airplanes". Farnborough Air Show. AINonline. July 24, 2008.
  • Bowles, Mark D.; Dawson, Virginia P. (1998). "Chapter 14: The advanced turboprop project: Radical innovation in a conservative environment". In Mack, Pamela (ed.). From engineering science to big science: The NACA and NASA Collier Trophy research project winners. NASA-SP. Vol. 4219. pp. 321–343. hdl:2060/20000012419. ISBN 978-0-16-049640-0. OCLC 757401658. Retrieved 25 September 2018.
  • Kuznetsov, N. D. (June 28–30, 1993). Propfan engines. Joint Propulsion Conference and Exhibit (29th ed.). Monterey, California, USA. doi:10.2514/6.1993-1981.
  • Kuntz, H. L.; Gatineau, R. J.; Prydz, R. A.; Balena, F. J. (October 1991). Development and testing of cabin sidewall acoustic resonators for the reduction of cabin tone levels in propfan-powered aircraft (Report). hdl:2060/19920004539. OCLC 976747507. alternate url
  • Kuntz, H. L.; Gatineau, R. J. (May 1991). Laboratory test and acoustic analysis of cabin treatment for Propfan Test Assessment aircraft (Report). OCLC 27904451. alternate url
  • United States Environmental Protection Agency (EPA) (August 1990). Preliminary technology cost estimates of measures available to reduce U.S. greenhouse gas emissions by 2010 (Report). Attachment D: Memo from Michael Kavanaugh on UDF aircraft engine.
  • Postlethwaite, Alan (April 18–24, 1990). "Opening doors: The Soviet aerospace industry is in transition as military cuts hit and its factories start producing consumer goods". Flight International. pp. 28–31.
  • Little, B. H.; Poland, D. T.; Bartel, H. W.; Withers, C. C.; Brown, P. C. (July 1989). Propfan test assessment (PTA): Final project report. Vol. NASA-CR-185138. hdl:2060/19900002423. OCLC 891598373. alternate url
  • Little, B. H.; Barrel, H. W.; Reddy, N. N.; Swift, G.; Withers, C. C.; Brown, P. C. (April 1989). Propfan test assessment (PTA): Flight test report. Vol. NASA-CR-182278. hdl:2060/19900002422. OCLC 57716217. alternate url
  • "Douglas holds back on propfan launch" (PDF). Flight International. Vol. 134, no. 4127. August 20, 1988. p. 12.
  • DeGeorge, C. L. (1988). Large-scale advanced prop-fan (LAP): Final report. Vol. NASA-CR-182112. hdl:2060/19880010922. OCLC 23092598. alternate url
  • 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. (PDF) from the original on March 13, 2017. Retrieved February 2, 2019. alternate url
  • GE Aircraft Engines (December 1987). Full scale technology demonstration of a modern counterrotating unducted fan engine concept. Design report. hdl:2060/19900000732. OCLC 1013402936 – via Internet Archive. alternate url
  • Donne, Michael (September 5, 1986). "The new aero-engines: A path to cheaper flight". Financial Times. Farnborough, England, United Kingdom. p. 20.
  • Moxon, Julian (May 24, 1986). "After the big turbofans". Civil Propulsion. Flight International. Vol. 129, no. 4012. pp. 32, 34. ISSN 0015-3710.
  • Skipp, Peter (December 14, 1985). "Tupolev and the new generation: Alexei Tupolev is looking ahead to a replacement for the Tu-154, the USSR's most widely-used short-to-medium-range jet airliner. He is also seeing into service a 154 derivative which will operate for many years to come". Flight International. pp. 30–31.
  • Whitlow, J. B., Jr.; Sievers, G. K. (September 10–11, 1984). Fuel savings potential of the NASA advanced turboprop program. Aviation Fuel Conservation Symposium. Federal Aviation Administration (FAA). Washington, D. C., USA. hdl:2060/19840021809. OCLC 11694598. alternate url
  • "Soviet designers look ahead". Flight International. February 13, 1982. p. 335.
  • Moxon, Julian (January 16, 1982). "Propfan: The propeller to replace jets?". Flight International. Windsor Locks, Connecticut, USA. pp. 112–114. ISSN 0015-3710.
  • Goldsmith, I. M. (February 1981). A study to define the research and technology requirements for advanced turbo/propfan transport aircraft. Vol. NASA-CR-166138. hdl:2060/19820010328. alternate url

External links

  • Variable pitch propfan. NASA Lewis Educational TV (Television production). 1987.
  • "Keith Henry archives collection: Prop-fan noise reduction and prop-fan propulsion research". NASA Cultural Resources (CRGIS). 3 February 2016. Retrieved April 25, 2019.
  • Aguilar, Hector; Haan, Leon de; Knuyt, Jerry; Nieuwendijk, Lisa (December 2017). "Propfan, an alternative for turbofan engines: Tackling the technical design characteristics of a propfan" (PDF). AviationFacts.eu. Aviation Academy at the Amsterdam University of Applied Sciences (AUAS). (PDF) from the original on 9 October 2018. Retrieved 9 October 2018.
  • Norris, Guy (June 12, 2007). "Green sky thinking - carbon credits and the propfan comeback?". Flight International. ISSN 0015-3710. from the original on June 21, 2007. Retrieved January 28, 2019.
  • Sandru, Mike (October 27, 2008). "A new 'open rotor' jet engine that could reduce fuel consumption". The Green Optimistic. from the original on December 17, 2018. Retrieved January 28, 2019.
  • Norris, Guy (June 25, 2021). "Evolutionary Trail Of The Open-Fan Engine". aviationweek.com. Retrieved 2021-06-28.

January 17, 2023
propfan, confused, with, turboprop, turbofan, propfan, also, called, open, rotor, engine, unducted, opposed, ducted, type, aircraft, engine, related, concept, both, turboprop, turbofan, distinct, from, both, design, intended, offer, speed, performance, turbofa. Not to be confused with turboprop or turbofan A propfan also called an open rotor engine or unducted fan as opposed to a ducted 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 A mockup of the GE36 at the Musee aeronautique et spatial Safran A closeup of the PW Allison 578 DX propfan demonstrator installed on the port side of a McDonnell Douglas MD 80 testbed Contents 1 Definition 2 History 2 1 1970s 1980s 2 1 1 Flight test programs 2 1 2 Other proposed applications 2 1 3 Decline 2 2 1990s 2 3 Twenty first century 3 Challenges 3 1 Blade design 3 2 Noise 3 2 1 Community noise 3 3 Size 3 4 Output rating 4 Aircraft with propfans 4 1 Proposed aircraft with propfans 5 See also 6 References 7 Bibliography 8 External linksDefinition Edit Propulsive efficiency comparison for various gas turbine engine configurations In the 1970s Hamilton Standard described its propfan as a small diameter highly loaded multiple bladed variable pitch propulsor having swept blades with thin advanced airfoil sections integrated with a nacelle contoured to retard the airflow through the blades thereby reducing compressibility losses and designed to operate with a turbine engine and using a single stage reduction gear resulting in high performance 1 In 1982 the weekly aviation magazine Flight International defined the propfan as a propeller with 8 10 highly swept blades that cruised at a speed of 390 480 knots 450 550 miles per hour 720 890 kilometres per hour 2 although its definition evolved a few years later with the emergence of contra rotating propfans 3 In 1986 British engine maker Rolls Royce used the term open rotor as a synonym for the original meaning of a propfan This action was to delineate the propfan engine type from a number of ducted engine proposals at the time that had propfan in their names 4 By the 2000s open rotor OR became a preferred term for propfan technology in research and news reports with contra rotating open rotor CROR also occasionally being used to distinguish between single rotation propfans As of 2015 the European Aviation Safety Agency EASA defined an open rotor concretely but broadly as a turbine engine fan stage that is not enclosed within a casing in contrast it had only a working definition of an open rotor engine the more commonly used term for propfan in the 21st century calling it a turbine engine featuring contra rotating fan stages not enclosed within a casing The engine uses a gas turbine to drive an unshrouded open contra rotating propeller like a turboprop but the design of the propeller itself is more tightly coupled to the turbine design and the two are certified as a single unit 5 El Sayed differentiates between turboprops and propfans according to 11 different criteria including number of blades blade shape tip speed bypass ratio Mach number and cruise altitude 6 History EditAbout a decade after German aerospace engineers began exploring the idea of using swept wings to reduce drag on transonic speed aircraft Hamilton Standard in the 1940s attempted to apply a similar concept to engine propellers It created highly swept propeller blades with supersonic tip speeds so that engines with exposed propellers could power aircraft to speeds and cruising altitudes only attained by new turbojet and turbofan engines Early tests of these blades revealed then unresolvable blade flutter and blade stress problems and high noise levels were considered another obstacle The popularity of turbojets and turbofans curtailed research in propellers but by the 1960s interest increased when studies showed that an exposed propeller driven by a gas turbine could power an airliner flying at a speed of Mach 0 7 0 8 and at an altitude of 35 000 feet 11 000 metres The term propfan was created during this period 7 One of the earliest engines that resembled the propfan concept was the 4 710 pounds force 21 0 kilonewtons Metrovick F 5 which featured twin contra rotating fans 14 blades in the fore front fan and 12 blades in the aft back fan at the rear of the engine and was first run in 1946 The blades however were mostly unswept 8 Other contra rotating propeller engines that featured on common aircraft included the four powerful Kuznetsov NK 12 engines each powering its own set of coaxial contra rotating propellers on the Soviet Union s Tupolev Tu 95 high speed military bomber and Antonov An 22 military transport aircraft and the Armstrong Siddeley Double Mamba ASMD engines both connected to a lone set of coaxial contra rotating propellers on the British Fairey Gannet anti submarine aircraft Both setups had four largely unswept blades in the front propeller and the back propeller 1970s 1980s Edit When the 1973 oil crisis caused petroleum price spikes in the early 1970s interest in propfans soared and NASA funded research began to accelerate 9 The propfan concept was outlined by Carl Rohrbach and Bruce Metzger of the Hamilton Standard division of United Technologies in 1975 10 and was patented by Rohrbach and Robert Cornell of Hamilton Standard in 1979 1 Later work by General Electric on similar propulsors adopted the name unducted fan which was a modified turbofan engine with the fan placed outside the engine nacelle on the same axis as the compressor blades During this era the propeller problems became fixable Advances were made in structural materials such as titanium metal and graphite and glass fiber composites infused with resin These materials replaced aluminum and steel metals in blade construction which allowed the blades to be made thinner and stronger 11 Computer aided design was also useful in refining blade characteristics Since the blades bend and deflect with higher power loading and centrifugal force the initial designs needed to be based on the in motion shape With the help of computers the blade designers would then work backward to find the optimal unloaded shape for manufacturing purposes 12 Flight test programs Edit Ground test installation of the Allison 501 M78 engine with an eight bladed 9 0 ft 2 7 m diameter Hamilton Standard propeller for the NASA Propfan Test Assessment Hamilton Standard the only large American manufacturer of aircraft propellers developed the propfan concept in the early 1970s 13 Hamilton Standard tested numerous variations in conjunction with NASA 14 15 Under the Propfan Test Assessment PTA program Lockheed Georgia proposed modifying a Gulfstream II to act as in flight testbed for the propfan concept while McDonnell Douglas proposed modifying a DC 9 for the same purpose 16 NASA chose the Lockheed proposal The Gulfstream II had a nacelle added to the left wing containing a 6 000 horsepower 4 500 kilowatts Allison 570 turboprop engine derived from the XT701 turboshaft developed for the Boeing Vertol XCH 62 heavy lift helicopter The engine used an eight bladed 9 foot diameter 2 7 metre 110 inch 270 centimetre single rotation Hamilton Standard SR 7 propfan The test engine which was named the Allison 501 M78 17 had a thrust rating of 9 000 lbf 40 kN 18 It was first operated in flight on March 28 1987 19 The extensive test program which cost about 56 million 20 racked up 73 flights and over 133 hours of flight time before finishing on March 25 1988 21 In 1989 however the testbed aircraft returned to the air from April 3 through April 14 to measure ground noise levels during flight 22 23 The engine was removed after that and the aircraft was converted to a space shuttle training aircraft later that year 24 The GE36 on a McDonnell Douglas MD 80 demonstrator at the 1988 Farnborough Air Show The gearless unducted fan engine had an overall diameter of 11 67 ft 3 56 m with either eight or ten blades in front depending on the particular configuration and eight blades in back The GE36 Unducted Fan UDF from American engine maker General Electric GE with 35 percent participation from French partner Snecma now Safran was a variation on the original propfan concept and resembled a pusher configuration piston engine GE s UDF had a novel direct drive arrangement where the reduction gearbox was replaced by a low speed seven stage free turbine One set of turbine rotors drove the forward set of propellers while the rear set was driven by the other set of rotors which rotated in the opposite direction The turbine had 14 blade rows with seven stages Each stage was a pair of contra rotating rows 25 Airframers who had been wary of issue prone gearboxes since the 1950s liked GE s gearless version of the propfan 12 Boeing intended to offer GE s pusher UDF engine on the 7J7 platform which would have had a cruise speed of Mach 0 83 26 and McDonnell Douglas planned to do likewise on their MD 94X airliner The GE36 was first flight tested mounted on the 3 engine station of a Boeing 727 100 on August 20 1986 27 The GE36 UDF for the 7J7 was planned to have a thrust of 25 000 pounds force 110 kN but GE claimed that in general its UDF concept could cover a thrust range of 9 000 to 75 000 lbf 40 to 334 kN 28 so a UDF engine could possibly match or surpass the thrust of the CF6 GE s family of widebody engines at that time McDonnell Douglas developed a proof of concept aircraft by modifying its company owned MD 80 which is suited for propfans due to its aft fuselage mounted engines like its DC 9 ancestor in preparation for the possible propfan powered MD 91 and MD 92 derivatives and a possible MD 94X clean sheet aircraft They replaced the left side JT8D turbofan engine with the GE36 Test flights began in May 1987 29 which proved the design s airworthiness aerodynamic characteristics and noise signature Following the initial tests a first class cabin was installed inside the aft fuselage and airline executives were offered the opportunity to experience the UDF powered aircraft first hand The test and marketing flights of the GE outfitted demonstrator aircraft concluded in 1988 exhibiting a 30 reduction in fuel consumption over turbo fan powered MD 80 full Stage 3 noise compliance and low levels of interior noise vibration The GE36 would have the same 25 000 lbf 110 kN thrust on the MD 92X but the same engine would be derated to 22 000 lbf 98 kN thrust for the smaller MD 91X The MD 80 was also successfully flight tested in April 1989 with the 578 DX propfan which was a prototype from the Allison Engine Company at that time a division of General Motors that was also derived from the Allison XT701 and built with Hamilton Standard propellers The engine program was jointly developed between Allison and another division of United Technologies the engine maker Pratt amp Whitney Unlike the competing GE36 UDF the 578 DX was fairly conventional having a reduction gearbox between the LP turbine and the propfan blades Due to jet fuel price drops and shifting marketing priorities Douglas shelved the propfan program later that year The PW Allison 578 DX engine installed on the same MD 80 testbed The contra rotating geared propfan engine is 11 6 ft 3 5 m in diameter with six blades in front and six blades in back Other proposed applications Edit Other announcements of future propfan powered airliners included The Fokker FXX a 100 120 seat propfan powered aircraft that was studied in 1982 30 The MPC 75 an 80 seat Mach 0 76 cruise speed 1 500 nmi range 1 700 mi 2 800 km regional aircraft conceived by Messerschmitt Bolkow Blohm MBB of West Germany and the Chinese Aero Technology Export Import Corporation CATIC used as the baseline powerplant two direct drive General Electric GE38 B5 UDF engines delivering 9 644 and 2 190 lbf 4 374 and 993 kgf 42 90 and 9 74 kN in static thrust and cruise with a thrust specific fuel consumption TSFC of 0 240 and 0 519 lb lbf h 6 8 and 14 7 g kN s respectively through an 85 in 2 1 m diameter propfan with 11 and 9 blades on the contra rotating propellers proposed as an alternative powerplant the 14 500 lbf 6 600 kgf 64 kN static thrust PW Allison 501 M80E geared propfan engine which was derived from the 501 M80C turboshaft that was chosen to power the United States Navy s Osprey tiltrotor aircraft 31 later described the propfan engine as one with the core from the T406 the military designation for the Osprey s powerplant containing a 108 in diameter 2 7 m propfan that provided 2 450 lbf 1 110 kgf 10 9 kN of thrust in cruise with a TSFC of 0 51 lb lbf h 14 g kN s 32 1090 The ATR 92 a 400 kn cruising speed 460 mph 740 km h five or six abreast 100 seat aircraft from Avions de Transport Regional ATR a joint venture between France s Aerospatiale and Italy s Aeritalia 33 and Spain s Construcciones Aeronauticas SA CASA 34 which would possibly be powered by the UDF 35 The Aerospatiale AS 100 a regional aircraft with a range of 1 500 nmi 1 700 mi 2 800 km a cruise speed of Mach 0 74 0 78 at 30 000 ft 9 100 m altitude 36 and a capacity of 80 100 seats that might be powered by the UDF 35 or by a propfan version of the Allison T406 34 tiltrotor engine The ATRA 90 Advanced Technology Regional Aircraft an 83 to 115 seat aircraft with a range of 1 500 2 100 nmi 1 700 2 400 mi 2 800 3 900 km and a cruise speed of Mach 0 8 at 30 000 ft 9 100 m altitude that was to be built by a multinational joint venture consisting of Industri Pesawat Terbang Nusantara IPTN of Indonesia Boeing USA MBB West Germany and Fokker Netherlands 36 The Tupolev Tu 334 a 126 seat aircraft that can travel 1 860 nmi 2 140 mi 3 450 km with 11 430 kg payload 25 200 lb 11 43 t 12 60 short ton which is powered by two Progress also known as Lotarev D 236 propfans 37 with a specific fuel burn of 0 46 kg kg thrust hour a cruise thrust of 1 6 tonnes force 3 500 lbf 16 kN and a static thrust of 8 to 9 tf 18 000 to 20 000 lbf 78 to 88 kN 38 The Ilyushin Il 88 a successor to the four turboprop Antonov An 12 tactical transporter that would be powered by two 11 000 hp 8 200 kW Progress D 236 propfans 39 The Ilyushin Il 118 an upgrade to the four turboprop Ilyushin Il 18 airliner 40 proposed in 1984 the aircraft would instead be powered by two D 236 propfans with the eight bladed front propeller on each engine rotating at a speed of 1 100 rpm and the six bladed back propeller turning at 1 000 rpm to lower noise and vibration 41 A re engined Antonov An 124 replacing the four Progress D 18T turbofans by 55 100 lbf thrust 245 2 kN Kuznetsov NK 62 propfans 42 Decline Edit None of these projects came to fruition however mainly because of excessive cabin noise compared to turbofans and low fuel prices 43 For General Electric the GE36 UDF was meant to replace the CFM56 high bypass turbofan that it produced with equal partner Snecma in their CFM International joint venture In the 1980s the engine was initially uncompetitive against the International Aero Engines rival offering the IAE V2500 In December 1986 the chairman of Snecma declared that the in development CFM56 5S2 would be the last turbofan created for the CFM56 family and that There is no point in spending more money on turbofans UDF is the future 44 The V2500 ran into technical problems in 1987 however and the CFM56 gained major sales momentum General Electric lost interest in having the GE36 cannibalize the CFM56 which went five years before it received its first order in 1979 and while the UDF could be made reliable by earlier standards turbofans were getting much much better than that General Electric added the UDF s blade technology directly into the GE90 the most powerful jet engine ever produced for the Boeing 777 45 1990s Edit The Progress D 236 propfan engine on the Yak 42E LL testbed aircraft at the Paris Air Show in 1991 At the beginning of the 1990s the Soviet Union Russia performed flight tests on the Progress D 236 a geared contra rotating propfan engine based on the core of the Progress D 36 turbofan with eight blades on the front propeller and six blades on the back propeller One testbed was a 10 100 hp 7 500 kW propfan mounted to an Ilyushin Il 76 and flown to the Hannover ILA 90 airshow which was intended for an unidentified four propfan aircraft 46 The D 236 flew 36 times for a total of 70 flight test hours on the Il 76 47 The other testbed was a 10 990 hp 8 195 kW 14 ft unit 4 2 m 170 in 420 cm mounted to a Yakovlev Yak 42E LL and flown to the 1991 Paris Air Show as a demonstration for the planned Yak 46 aircraft with twin propfan engines 48 which in its base 150 seat version would have a range of 1 900 nmi 2 200 mi 3 500 km and cruise at a speed of 460 kn 530 mph 850 km h 780 ft s 240 m s 49 Mach 0 75 50 The Soviets claimed the D 236 had a true aerodynamic efficiency of 28 percent and a fuel savings of 30 percent over an equivalent turboprop They also revealed plans for propfans with power ratings of 14 100 and 30 200 hp 10 500 and 22 500 kW 46 Progress D27 Propfans fitted to an Antonov An 70 Like the Progress D 236 the more powerful Progress D 27 propfan engine is a contra rotating propfan with eight front blades and six back blades 50 but the D 27 has advanced composite blades with a reduced thickness to chord ratio and a more pronounced curvature at the leading edge 51 An engine that was launched in 1985 the D 27 52 delivers 14 000 hp 10 440 kW of power with 27 000 lbf 119 kN of thrust at takeoff 53 Two rear mounted D 27 propfans propelled the Ukrainian Antonov An 180 which was scheduled for a 1995 first flight and a 1997 entry into service 54 In January 1994 Antonov rolled out the first prototype of the An 70 military transport aircraft powered by four Progress D 27s attached to wings mounted to the top of the fuselage 53 The Russian Air Force placed an order for 164 aircraft in 2003 later canceled As of 2013 the An 70 was still thought to have a promising future as a freighter 55 However since the propeller component of the Progress D 27 is made by Russia s SPE Aerosila the An 70 was stymied by Ukraine s political conflict with Russia Instead Antonov began working with Turkey in 2018 to redevelop the An 70 as a rebranded An 77 so that the aircraft can comply with modern day requirements without Russian supplier participation 56 Twenty first century Edit In the first decade of the 21st century rising jet fuel prices increased emphasis on engine airframe efficiency to reduce emissions which renewed interest in the propfan concept for jetliners beyond the Boeing 787 and Airbus A350XWB For instance Airbus patented aircraft designs with twin rear mounted contra rotating propfans 57 Rolls Royce had the rear pusher configured RB 509 11 and front tractor configured RB 509 14 geared propfan designs which produced 15 000 25 000 lbf thrust 6 800 11 300 kgf 67 111 kN using the gas generator from its XG 40 engine 58 with 13 000 hp 9 700 kW of shaft power 59 It became lukewarm on propfan technology in the 1980s 60 although it developed an open rotor design that was thought to be a finalist for the Irkut MS 21 narrowbody aircraft 61 The Rolls Royce RB3011 engine would have a diameter of about 170 in 430 cm 14 ft 4 3 m and require a 16 000 shaft hp 12 000 kW gearbox 62 Safran open rotor mockup in 2017 The European Commission launched an Open Rotor demonstration in 2008 led by Safran within the Clean Sky program funded with 65 million euros over eight years A demonstrator was assembled in 2015 and ground tested in May 2017 on its open air test rig in Istres aiming to reduce fuel consumption and associated CO2 emissions by 30 compared with current CFM56 turbofans 63 After the completion of ground testing at the end of 2017 Safran s geared open rotor engine had reached technology readiness level 5 64 The demonstrator s twelve blade front propeller and ten blade back propeller had diameters of 13 1 and 12 5 ft 4 0 and 3 8 m 160 and 150 in 400 and 380 cm respectively The demonstrator based on the core of the Snecma M88 military fighter engine uses up to 12 200 horsepower 9 megawatts provides a thrust of about 22 000 lbf 100 kN and would cruise at a speed of Mach 0 75 65 Safran s future open rotor engine however would have a maximum diameter of almost 14 8 ft 4 50 m 177 in 450 cm 66 In 2007 the Progress D 27 was successfully modified to meet the United States Federal Aviation Administration FAA Stage 4 regulations which correspond to International Civil Aviation Organization ICAO Chapter 4 standards 67 A 2012 trade study projected that propfan noise would be 10 13 decibels quieter than allowed by Stage 4 regulations 68 Stage 5 noise limits reduce the limits by only seven effective perceived noise decibels EPNdB 69 within the propfan noise envelope The study also projected that open rotors would be nine percent more fuel efficient but remain 10 12 decibels louder than turbofans 68 Snecma claimed that its propfan engines would have about the same noise levels as its CFM LEAP turbofan engine 70 In 2021 CFM announced its Revolutionary Innovation for Sustainable Engines RISE development program to produce a single stage gear driven propfan paired with active stators in a puller tractor configuration with flight tests to begin by 2025 The rotor was expected to be 12 13 ft 3 7 4 0 m in diameter The engine was expected to produce 20 000 35 000 lbf 9 100 15 900 kgf 89 156 kN of thrust with a 20 increase in fuel efficiency The company claimed its motivation was the global emphasis on reducing emissions The engine was planned to support both hydrogen and sustainable aviation fuels The engine was expected to include a compact high pressure core and a recuperating system to preheat combustion air with exhaust heat along with ceramic matrix composites in the hot section and resin transfer molded composite fan blades In addition to the rotor the design includes a nonrotating set of variable pitch stator blades that act as flow recovery vanes The design increases the fan pressure ratio and reduces rotor loading increasing airspeed The fan stage is to be powered by a high speed booster compressor and a high speed low pressure shaft driven front gearbox The engine is slated for certification as an integrated engine instead of a traditional propeller engine because of its airframe integration complexity 71 CFM planned for an aerodynamically three dimensional rotor with 12 woven carbon fiber composite blades Aided by a smaller engine core the CFM RISE engine would have a bypass ratio of 75 72 Challenges EditBlade design Edit Turboprops have an optimum speed below about 450 mph 390 kn 720 km h 73 because propellers lose efficiency at high speed due to an effect known as wave drag that occurs just below supersonic speeds This powerful drag has a sudden onset and it led to the concept of a sound barrier when first encountered in the 1940s This effect can happen whenever the propeller is spun fast enough that the blade tips approach the speed of sound The most effective way to address this problem is by adding blades to the propeller allowing it to deliver more power at a lower rotational speed This is why many World War II fighter designs started with two or three blade propellers but by the end of the war were using up to five blades as the engines were upgraded new propellers were needed to more efficiently convert that power Adding blades makes the propeller harder to balance and maintain and the additional blades cause minor performance penalties due to drag and efficiency issues But even with these sorts of measures eventually the forward speed of the plane combined with the rotational speed of the propeller blade tips together known as the helical tip speed will again result in wave drag problems For most aircraft this will occur at speeds over about 450 mph 390 kn 720 km h Swept propeller A method of decreasing wave drag was discovered by German researchers in 1935 sweeping the wing backwards Today almost all aircraft designed to fly much above 450 mph 390 kn 720 km h use a swept wing Since the inside of the propeller is moving slower in the rotational direction than the outside the blade is progressively more swept back toward the outside leading to a curved shape similar to a scimitar a practice that was first used as far back as 1909 in the Chauviere two bladed wood propeller used on the Bleriot XI At the blade root the blade is actually swept forward into the rotational direction to counter the twisting that is generated by the backward swept blade tips 74 The Hamilton Standard test propfan was swept progressively to a 39 degree maximum at the blade tips allowing the propfan to produce thrust even though the blades had a helical tip speed of about Mach 1 15 75 The blades of the GE36 UDF and the 578 DX have a maximum tip speed in rotation of about 750 800 ft s 230 240 m s 510 550 mph 820 880 km h 76 or about half the maximum tip speed for the propeller blades of a conventional turbofan 77 That maximum blade tip speed would be kept constant despite wider or narrower propeller diameter resulting in an RPM reduction or increase respectively 3 Drag can also be reduced by making the blades thinner which increases the speed that the blades can attain before the air ahead of them becomes compressible and causes shock waves For example the blades of the Hamilton Standard test propfan had a thickness to chord ratio that tapered from less than 20 at the spinner junction to 2 at the tips and 4 at mid span 75 Propfan blades had approximately half the thickness to chord ratio of the best conventional propeller blades of the era 78 thinned to razor like sharpness at their edges 12 79 and weighed as little as 20 pounds 9 1 kg 80 The GE36 UDF engine that was tested on the Boeing 727 had front and back blades that weighed 22 5 and 21 5 lb 10 2 and 9 8 kg each 81 A comparison of the propfan with other types of aircraft engines Noise Edit One of the major problems with the propfan is noise The propfan research in the 1980s discovered ways to reduce noise but at the cost of reduced fuel efficiency mitigating some of the advantages of a propfan General methods for reducing noise include lowering tip speeds and decreasing blade loading or the amount of thrust per unit of blade surface area A concept similar to wing loading blade loading can be reduced by lowering the thrust requirement or by increasing the amount width and or length of the blades For contra rotating propfans which can be louder than turboprops or single rotating propfans noise can also be lowered by 82 increasing the gap between the propellers keeping back propeller blade lengths shorter than those of the front propeller so that the back propeller blades avoid cutting through the blade tip vortices of the front propeller blade vortex interaction using different numbers of blades on the two propellers to avoid acoustic reinforcement and turning the front propeller and back propeller at different speeds also to prevent acoustic reinforcement 41 Community noise Edit Engine makers expect propfan implementations to meet community as opposed to cabin noise regulations without sacrificing the efficiency advantage Some think that propfans can potentially cause less of a community impact than turbofans given their lower rotational speeds Geared propfans should have an advantage over ungeared propfans for the same reason 83 In 2007 the Progress D 27 was successfully modified to meet the United States Federal Aviation Administration FAA Stage 4 regulations which correspond to International Civil Aviation Organization ICAO Chapter 4 standards and were adopted in 2006 67 A 2012 trade study projected that noise from existing open rotor technology would be 10 13 decibels quieter than the maximum noise level allowed by the Stage 4 regulations 68 the newer Stage 5 noise limits which replaced the Stage 4 regulations for larger aircraft in 2018 and mirrored the ICAO Chapter 14 noise standard established in 2014 are more restrictive than the Stage 4 requirement by only seven effective perceived noise decibels EPNdB 69 so current propfan technology shouldn t be hindered by the Stage 5 standards The study also projected that at existing technology levels open rotors would be nine percent more fuel efficient but remain 10 12 decibels louder than turbofans 68 Snecma however maintains that open rotor tests show that its propfan engines would have about the same noise levels as its CFM LEAP turbofan engine 70 which entered service in 2016 Further reductions can be achieved by redesigning the aircraft structure to shield noise from the ground For example another study estimated that if propfan engines were used to power a hybrid wing body aircraft instead of a conventional tube and wing aircraft noise levels could be reduced by as much as 38 EPNdB compared to ICAO Chapter 4 requirements 84 In 2007 the British budget airline easyJet introduced its ecoJet concept a 150 250 seat aircraft with V mounted open rotor engines joined to the rear fuselage and shielded by a U tail 85 It unsuccessfully initiated discussions with Airbus Boeing and Rolls Royce to produce the aircraft 86 Size Edit A twin engine aircraft carrying 100 150 passengers would require propfan diameters of 120 168 inches 300 430 cm 10 0 14 0 ft 3 0 4 3 m 75 and a propfan with a propeller diameter of 236 in 600 cm 19 7 ft 6 0 m would theoretically produce almost 60 000 lbf 270 kN of thrust 87 These sizes achieve the desired high bypass ratios of over 30 but they are approximately twice the diameter of turbofan engines of equivalent capability 65 For this reason airframers usually design the empennage with a T tail configuration for aerodynamic purposes and the propfans may be attached to the upper part of the rear fuselage For the Rolls Royce RB3011 propfan prototype a pylon of about 8 3 ft 2 54 m 100 in 254 cm long would be required to connect the center of each engine to the side of the fuselage 88 If the propfans are mounted to the wings the wings would be attached to the aircraft in a high wing configuration which allows for ground clearance without requiring excessively long landing gear For the same amount of power or thrust produced an unducted fan requires shorter blades than a geared propfan 89 although the overall installation issues still apply Output rating Edit Turboprops and most propfans are rated by the amount of shaft horsepower shp that they produce as opposed to turbofans and the UDF propfan type which are rated by the amount of thrust they put out The rule of thumb is that at sea level with a static engine 1 shaft horsepower 750 watts is roughly equivalent of 2 pounds force 8 9 N thrust but at cruise altitude that changes to about 1 pound force 4 4 N thrust That means two 25 000 lbf thrust 110 kN engines can theoretically be replaced with a pair of 12 000 13 000 shaft hp 8 900 9 700 kW propfans or with two 25 000 lbf thrust 110 kN UDF propfans 3 Aircraft with propfans EditMain category Propfan powered aircraft Antonov An 70 Proposed aircraft with propfans Edit Antonov An 180 ATRA 90 Boeing 7J7 McDonnell Douglas MD 94X MPC 75 Yakovlev Yak 44 Yakovlev Yak 46See also EditTurboprop Contra rotating propeller Contra rotating Ducted fan Geared turbofan Comparable engines Europrop TP400 General Electric GE 36 UDF Kuznetsov NK 12 Kuznetsov NK 93 Metrovick F 5 Pratt amp Whitney Allison 578 DX Progress D 27 Progress D 236 Rolls Royce RB3011 Related lists List of aircraft enginesReferences Edit a b US 4171183 Cornell Robert W amp Rohrbach Carl Multi bladed high speed prop fan published 16 Oct 1979 assigned to United Technologies Corporation What is propfan Flight International January 16 1982 p 113 ISSN 0015 3710 a b c Propfan UDF some answers questioned Paris Review Flight International June 15 1985 pp 8 9 Retrieved March 28 2019 Propfans the genie is out of the bottle PDF Air Transport Flight International Vol 129 no 3999 New Delhi India February 22 1986 p 8 Retrieved May 17 2019 EASA 2015 pp 5 6 El Sayed Ahmed F July 6 2017 Aircraft propulsion and gas turbine engines 2nd ed CRC Press Table 6 11 ISBN 9781466595187 OCLC 986784025 Kuntz et al pp 2 to 3 Metrovick F 5 Open fan thrust augmenter on standard F 2 gas generator Flight January 2 1947 p 18 Archived PDF from the original on November 7 2017 Retrieved March 28 2019 Kuntz et al p 3 Rohrbach C Metzger F B September 29 October 1 1975 The Prop Fan A new look in propulsors 11th Propulsion Conference Vol 75 1208 Anaheim California American Institute of Aeronautics and Astronautics AIAA and Society of Automotive Engineers SAE doi 10 2514 6 1975 1208 Ferrell J E October 12 1986 Propfan gets another whirl San Francisco Examiner Retrieved April 25 2019 via Chicago Tribune a b c Schefter Jim March 1985 So long jets Ingenious new blades make propliners as fast as jets Cover story Popular Science Vol 226 no 3 pp 66 69 ISSN 0161 7370 Wilford John Noble August 24 1982 Sleek high performance designs give propellers a future after all Science Times New York Times Edwards Air Force Base California USA p C1 ISSN 0362 4331 Rohrbach Carl July 26 29 1976 A report on the aerodynamic design and wind tunnel test of a Prop Fan model 12th Propulsion Conference Vol 76 667 Palo Alto California American Institute of Aeronautics and Astronautics AIAA and Society of Automotive Engineers SAE doi 10 2514 6 1976 667 Jeracki Robert J Mikkelson Daniel C Blaha Bernard J April 3 6 1979 Wind tunnel performance of four energy efficient propellers designed for Mach 0 8 cruise SAE Business Aircraft Meeting and Exposition Vol 790573 Wichita Kansas Society of Automotive Engineers SAE doi 10 4271 790573 hdl 2060 19790011898 OCLC 37181399 Goldsmith 1981 Propfanned G2 takes to the air PDF World News Flight International Vol 131 no 4061 Marietta Georgia USA May 9 1987 p 2 ISSN 0015 3710 Hager amp Vrabel 1988 p 56 Gulfstream flies with propfan PDF Propulsion Flight International Vol 131 no 4062 May 16 1987 p 16 ISSN 0015 3710 Propfan acoustic tests completed PDF Flight International Vol 133 no 4114 May 21 1988 p 37 ISSN 0015 3710 Poland D T Bartel H W Brown P C July 11 13 1988 PTA flight test overview Joint Propulsion Conference 24th ed Boston Massachusetts USA doi 10 2514 6 1988 2803 OCLC 1109689683 Rickley E J September 1989 En route noise NASA propfan test aircraft calculated source noise Report Washington D C U S Department of Transportation DOT Federal Aviation Administration FAA Office of Environment pp 41 59 alternate url Garber Donald P Willshire William L Jr September 1994 En route noise levels from Propfan Test Assessment airplane Report Hampton Virginia National Aeronautics and Space Administration NASA alternate url NASA shuttle training aircraft Texas Air amp Space Museum Retrieved July 18 2019 GE Aircraft Engines 1987 Manufacturers positioning for coming competitive battles Air Transport World No September 1986 Farnborough England United Kingdom pp 20 ISSN 0002 2543 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 s UDF flies again PDF Air Transport Flight International Vol 130 no 4027 Mojave California USA September 6 1986 p 23 ISSN 0015 3710 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 Warwick Graham August 15 1987 UHB the acid test Flight International pp 22 23 Retrieved March 22 2019 Delta demands 150 seater as MDF 100 dies PDF Air transport Flight International Vol 121 no 3798 February 20 1982 p 404 ISSN 0015 3710 MBB CATIC Association July 1987 MPC 75 feasibility study summary report B1 project definition PDF Report Fischer B Chen J Z September 20 25 1992 MPC75 The evolution of a new regional airliner for the late nineties PDF Congress of the International Council of the Aeronautical Sciences 18th ed Beijing People s Republic of China pp 1084 1093 OCLC 761191715 ATR plans 100 seater PDF Farnborough First News Flight International Farnborough England United Kingdom September 10 1988 p 16 ISSN 0015 3710 a b Sedbon Gilbert December 17 1988 Spain joins ATR 92 study PDF Flight International Paris France p 14 ISSN 0015 3710 a b Snecma raises propfan funds Air Transport Flight International Vol 132 no 4086 Paris France October 31 1987 p 6 ISSN 0015 3710 a b Propfan aircraft PDF Developments Science and Technology Perspectives Vol 2 no 12 Foreign Broadcast Information Service published August 21 1987 Air and Cosmos June 20 1987 p 2 OCLC 13857080 Archived from the original PDF on January 23 2017 TU 134 replacement decision due Moscow Aerospace 90 Flight International Vol 138 no 4237 October 10 16 1990 p 28 ISSN 0015 3710 Postlethwaite Alan April 29 1989 Tupolev unveils propfan airliner Flight International Vol 135 no 4162 Moscow Soviet Union p 10 ISSN 0015 3710 Ilyushin Il 276 SVTS Ruslet Great Encyclopedia of Russian and Chinese Aviation in Russian Retrieved April 23 2019 Ilyushin IL 18 Coot Turboprop powered passenger airliner maritime reconnaissance platform Archived from the original on March 9 2019 Retrieved April 23 2019 a b Gordon Yefim Komissarov Dmitriy 2003 Ilyushin IL 18 20 22 A versatile turboprop transport Aerofax p 47 ISBN 9781857801576 OCLC 52195311 NK 62 NK 63 Kuznetsov USSR in Czech Flight International 2007 07 12 Whatever happened to propfans Archived from the original on October 20 2007 Retrieved January 28 2019 France backs UDF Propulsion Flight International Vol 130 no 4042 Villaroche France December 20 1986 p 63 ISSN 0015 3710 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 amp Space Smithsonian Magazine Vol 20 no 3 pp 42 49 ISSN 0886 2257 OCLC 109549426 Archived from the original on August 14 2017 Retrieved January 28 2019 a b Soviets show Il 76 mounted propfan Flight International Vol 137 no 4217 May 23 29 1990 p 9 ISSN 0015 3710 Komissarov Dmitriy Gordon Yefim 2001 Ilyushin IL 76 Russia s versatile airlifter Aerofax pp 43 45 ISBN 9781857801064 OCLC 47676935 Yak propfan pops into Paris Paris Show Report Flight International Vol 140 no 4272 June 26 July 2 1991 p 16 ISSN 0015 3710 Rybak Boris May 22 28 1991 Yakovlev takes propfan lead While development of fuel saving propfan engines languishes in the West work continues in the Soviet Union where recent fuel shortages have underscored the need for new engine technology Commercial Engines Flight International Vol 139 no 4267 pp 27 28 ISSN 0015 3710 a b Postlethwaite Alan May 9 15 1990 Yakovlev strikes back Propfan and other high technology derivatives of the Yak 42 airliner NATO codename Clobber are planned Flight International Vol 137 no 4215 pp 61 62 65 66 ISSN 0015 3710 More detailed information about D 27 engine SE Ivchenko Progress Archived from the original on 2013 01 26 Retrieved 2012 06 29 Dmytriyev Sergiy October 12 14 2015 Ivchenko Progress innovations for turboprop engines PDF 5th Symposium on Collaboration in Aircraft Design Naples Italy Archived PDF from the original on April 19 2019 a b Velovich Alexander February 9 15 1994 Against all odds Despite having to toil in a cold economic climate Antonov has rolled out the first of what it hopes will be many of its An 70 four engine transport aircraft Antonov An 70 Flight International Vol 145 no 4407 pp 34 35 ISSN 0015 3710 An 180 project by ANTK O K Antonov Freighter of the future Air Cargo World February 15 2013 Manufacturers news PDF Civil News Scramble No 471 Dutch Aviation Society August 2018 p 38 Archived from the original PDF on May 2 2019 US application 2009020643 Airbus amp Christophe Cros Aircraft having reduced environmental impact published 2009 01 22 Alekseyev Col Yu 1988 Propfan engines Zarubezhnoye Voyennoye Obozreniye Moscow Soviet Union Ministry of Defense published March 21 1989 10 27 29 OCLC 946659244 via Soviet Union Foreign Military Review United Kingdom aerospace and weapons projects Gas turbines Archived from the original on March 5 2013 Retrieved April 30 2019 Colchester Nicholas March 24 1986 Elegance is key to cut and thrust Technology Financial Times p 12 Karnozov Vladimir September 3 2008 Yakovlev ready to call for MS 21 systems tenders as design freeze nears Flight International Moscow Russia Butterworth Hayes Philip March 2010 Open rotor research revs up PDF Aerospace America Vol 48 no 3 pp 38 42 ISSN 0740 722X OCLC 664005753 Archived from the original PDF on April 2 2015 Safran celebrates successful start of Open Rotor demonstrator tests on new open air test rig in southern France Press release Safran October 3 2017 Archived from the original on August 29 2018 Retrieved October 3 2017 Angrand Antony May 10 2019 Safran ponders open rotor options Air amp Cosmos International No 7 pp 22 23 ISSN 1240 3113 via Issuu a b Ebner Ulrike February 14 2018 Treibstoff sparwunder Open rotor Flug Revue in German Archived from the original on March 29 2019 Cueille Stephane March 25 2019 What does the future hold in store for the Open Rotor Archived from the original on March 29 2019 Retrieved March 29 2019 via Safran a b Karnozov Vladimir May 1 2007 Military engines Development thrusts Flight International Moscow Russia ISSN 0015 3710 Archived from the original on April 2 2016 a b c d Croft John July 5 2012 Open rotor noise not a barrier to entry GE Flight International Archived from the original on July 18 2012 Retrieved July 21 2012 a b 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 a b Eshel Tamir January 2 2014 Snecma tests open rotor engine Defense Update Archived from the original on July 3 2017 Retrieved April 10 2019 Norris Guy Dubois Thierry June 25 2021 CFM Details Open Fan Plan For Next gen Engine Aviation Week Archived from the original on 2021 07 09 Retrieved 2021 06 30 Kjelgaard Chris November 10 2021 Commercial engine OEMs detail emissions work Dubai Airshow AINonline Spakovszky Zoltan 2009 Unified propulsion lecture 1 Unified Engineering Lecture Notes MIT Archived from the original on March 31 2018 Retrieved 2009 04 03 Garrison Peter February 1990 Props and circumstance Technicalities Flying Vol 117 no 2 a b c Hammitt Tom June 1985 Ace of blades Their radical shapes hiding a conservative streak propfans could combine fanjet speed with propeller efficiency Flying Vol 112 no 6 pp 66 68 70 Retrieved March 28 2019 Date set for Allison UHB flight test Propulsion Flight International Long Beach California USA February 8 1986 pp 50 51 Archived from the original on March 27 2019 Retrieved March 28 2019 The fans are flying Farnborough Report Flight International September 13 1986 pp 18 20 Retrieved March 25 2019 Hager amp Vrabel 1988 p 6 Nesbitt Jim September 22 1985 Jet engines propel into new era Orlando Sentinel Marietta Georgia USA Archived from the original on March 30 2019 Retrieved March 29 2019 Moll Nigel May 1987 7J7 The next new Boeing Flying pp 37 39 GE Aircraft Engines 1987 p 163 Hager amp Vrabel 1988 p 82 Warwick Graham Moxon Julian May 23 1987 The power of persuasion Flight International Washington DC USA pp 39 41 Trimble Stephen February 12 2014 Analysis Noise goals in sight for open rotor researchers News Flight International Washington D C USA p 28 ISSN 0015 3710 The easyJet ecoJet to cut CO2 emissions by 50 by 2015 easyJet airline company ltd Archived from the original on June 16 2007 Retrieved December 30 2017 Robinson Tim October 6 2017 Can easyJet short circuit electric airliner flight Royal Aeronautical Society Learmount David August 30 1986 US air transport technology where next Flight International pp 120 122 124 128 Retrieved March 28 2019 Doyle Andrew October 5 2009 Keeping options open Flight International London England United Kingdom 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 Geographic Information Systems GIS Team General resources Prop fan propulsion concepts Technology Review Design Methodology State of the art designs and future outlook Raymond Scott Ciszek University of Virginia Department of Mechanical and Aerospace Engineering Senior Thesis Project March 25 2002Bibliography EditDubois Thierry Warwick Graham January 9 22 2017 Last of the CRORs Safran is about to test a counter rotating open rotor engine despite waning appeal Advanced Propulsion Aviation Week amp Space Technology Vol 179 no 1 Lyon France and Washington D C USA p 54 OCLC 969306167 Kinney Jeremy R 2017 4 The Quest for Propulsive Efficiency 1976 1989 PDF The power for flight NASA s contributions to aircraft propulsion NASA aeronautics book series Vol 631 pp 114 125 hdl 2060 20180003207 ISBN 9781626830370 OCLC 990183146 alternate url Notice of proposed amendment NPA 2015 22 Open rotor engine and installation PDF European Aviation Safety Agency December 21 2015 archived PDF from the original on August 25 2018 retrieved March 28 2019 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 Coniglio Sergio February 2010 Military aircraft propulsion Jets vs props Military Technology MILTECH Vol 34 no 2 Monch Publishing Group pp 77 84 ISSN 0722 3226 OCLC 527912380 Bowles Mark 2010 Advanced turboprops and laminar flow PDF The Apollo of aeronautics NASA s aircraft energy efficiency program 1973 1987 NASA SP Vol 2009 574 Washington D C National Aeronautics and Space Administration pp 122 136 hdl 2060 20110011568 ISBN 9780160842955 OCLC 465190382 Retrieved 25 September 2018 alternate url Doyle Andrew October 6 2009 Open rotor how does it work Flight International London England UK ISSN 0015 3710 Turner Aimee March 23 2009 Back to the windtunnel Flight International London England United Kingdom EU explores cleaner airplanes Farnborough Air Show AINonline July 24 2008 Bowles Mark D Dawson Virginia P 1998 Chapter 14 The advanced turboprop project Radical innovation in a conservative environment In Mack Pamela ed From engineering science to big science The NACA and NASA Collier Trophy research project winners NASA SP Vol 4219 pp 321 343 hdl 2060 20000012419 ISBN 978 0 16 049640 0 OCLC 757401658 Retrieved 25 September 2018 Kuznetsov N D June 28 30 1993 Propfan engines Joint Propulsion Conference and Exhibit 29th ed Monterey California USA doi 10 2514 6 1993 1981 Kuntz H L Gatineau R J Prydz R A Balena F J October 1991 Development and testing of cabin sidewall acoustic resonators for the reduction of cabin tone levels in propfan powered aircraft Report hdl 2060 19920004539 OCLC 976747507 alternate url Kuntz H L Gatineau R J May 1991 Laboratory test and acoustic analysis of cabin treatment for Propfan Test Assessment aircraft Report OCLC 27904451 alternate url United States Environmental Protection Agency EPA August 1990 Preliminary technology cost estimates of measures available to reduce U S greenhouse gas emissions by 2010 Report Attachment D Memo from Michael Kavanaugh on UDF aircraft engine Postlethwaite Alan April 18 24 1990 Opening doors The Soviet aerospace industry is in transition as military cuts hit and its factories start producing consumer goods Flight International pp 28 31 Little B H Poland D T Bartel H W Withers C C Brown P C July 1989 Propfan test assessment PTA Final project report Vol NASA CR 185138 hdl 2060 19900002423 OCLC 891598373 alternate url Little B H Barrel H W Reddy N N Swift G Withers C C Brown P C April 1989 Propfan test assessment PTA Flight test report Vol NASA CR 182278 hdl 2060 19900002422 OCLC 57716217 alternate url Douglas holds back on propfan launch PDF Flight International Vol 134 no 4127 August 20 1988 p 12 DeGeorge C L 1988 Large scale advanced prop fan LAP Final report Vol NASA CR 182112 hdl 2060 19880010922 OCLC 23092598 alternate url 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 alternate url GE Aircraft Engines December 1987 Full scale technology demonstration of a modern counterrotating unducted fan engine concept Design report hdl 2060 19900000732 OCLC 1013402936 via Internet Archive alternate url Donne Michael September 5 1986 The new aero engines A path to cheaper flight Financial Times Farnborough England United Kingdom p 20 Moxon Julian May 24 1986 After the big turbofans Civil Propulsion Flight International Vol 129 no 4012 pp 32 34 ISSN 0015 3710 Skipp Peter December 14 1985 Tupolev and the new generation Alexei Tupolev is looking ahead to a replacement for the Tu 154 the USSR s most widely used short to medium range jet airliner He is also seeing into service a 154 derivative which will operate for many years to come Flight International pp 30 31 Whitlow J B Jr Sievers G K September 10 11 1984 Fuel savings potential of the NASA advanced turboprop program Aviation Fuel Conservation Symposium Federal Aviation Administration FAA Washington D C USA hdl 2060 19840021809 OCLC 11694598 alternate url Soviet designers look ahead Flight International February 13 1982 p 335 Moxon Julian January 16 1982 Propfan The propeller to replace jets Flight International Windsor Locks Connecticut USA pp 112 114 ISSN 0015 3710 Goldsmith I M February 1981 A study to define the research and technology requirements for advanced turbo propfan transport aircraft Vol NASA CR 166138 hdl 2060 19820010328 alternate urlExternal links EditVariable pitch propfan NASA Lewis Educational TV Television production 1987 Keith Henry archives collection Prop fan noise reduction and prop fan propulsion research NASA Cultural Resources CRGIS 3 February 2016 Retrieved April 25 2019 Aguilar Hector Haan Leon de Knuyt Jerry Nieuwendijk Lisa December 2017 Propfan an alternative for turbofan engines Tackling the technical design characteristics of a propfan PDF AviationFacts eu Aviation Academy at the Amsterdam University of Applied Sciences AUAS Archived PDF from the original on 9 October 2018 Retrieved 9 October 2018 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 Sandru Mike October 27 2008 A new open rotor jet engine that could reduce fuel consumption The Green Optimistic Archived from the original on December 17 2018 Retrieved January 28 2019 Norris Guy June 25 2021 Evolutionary Trail Of The Open Fan Engine aviationweek com Retrieved 2021 06 28 Retrieved from https en wikipedia org w index php title Propfan amp oldid 1127079329, wikipedia, wiki, book, books, library,

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