Misplaced Pages

#80919

96-471: The CFM International RISE ("Revolutionary Innovation for Sustainable Engines") is an open rotor engine currently under development by CFM International , a 50–50 joint venture between American GE Aerospace and French Safran Aircraft Engines . The engine is planned to support both hydrogen and sustainable aviation fuels , and plans are to achieve a 20% reduction in fuel burn and carbon dioxide emissions compared to similar earlier experimental designs by

192-544: A GE F110 military test engine. As of late 2023, GE was producing test parts toward the goal of producing a demonstrator engine for flight testing . The demonstrator would pair an open fan set with a GE Passport gas generator. Unlike the GE36 and PW-Allison 578-DX contra-rotating engines that were proposed in the 1980s and Safran's open rotor engine in the 2010s, the RISE has only a single-stage open rotor. The open rotor stage

288-433: 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. 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 . About

384-480: 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". 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), although its definition evolved

480-525: 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

576-689: 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 aircraft 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

672-575: A few years later with the emergence of contra-rotating propfans. 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. 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,

768-531: 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). 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, but the D-27 has advanced composite blades with a reduced thickness-to-chord ratio and

864-400: A gear train has two gears. The input gear (also known as the drive gear or driver ) transmits power to the output gear (also known as the driven gear ). The input gear will typically be connected to a power source, such as a motor or engine. In such an example, the output of torque and rotational speed from the output (driven) gear depend on the ratio of the dimensions of the two gears or

960-493: A more pronounced curvature at the leading edge . An engine that was launched in 1985, the D-27 delivers 14,000 hp (10,440 kW) of power with 27,000 lbf (119 kN) of thrust at takeoff. 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. In January 1994, Antonov rolled out the first prototype of

1056-464: 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. General resources Reduction gear A gear train or gear set is a machine element of a mechanical system formed by mounting two or more gears on a frame such that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, providing

SECTION 10

#1732786625081

1152-426: A pair of meshing gears, the angular speed ratio , also known as the gear ratio , can be computed from the ratio of the pitch radii or the ratio of the number of teeth on each gear. Define the angular speed ratio R A B {\displaystyle R_{AB}} of two meshed gears A and B as the ratio of the magnitude of their respective angular velocities: Here, subscripts are used to designate

1248-464: A pitch circle radius of 2 in (51 mm), the angular speed ratio R A B {\displaystyle R_{AB}} is 2, which is sometimes written as 2:1. Gear A turns at twice the speed of gear B . For every complete revolution of gear A (360°), gear B makes half a revolution (180°). In addition, consider that in order to mesh smoothly and turn without slipping, these two gears A and B must have compatible teeth. Given

1344-533: 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, which proved the design's airworthiness, aerodynamic characteristics, and noise signature. Following

1440-432: 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. These sizes achieve the desired high bypass ratios of over 30, but they are approximately twice the diameter of turbofan engines of equivalent capability. For this reason, airframers usually design the empennage with a T-tail configuration in order to avoid

1536-546: A smooth transmission of rotation from one gear to the next. Features of gears and gear trains include: The transmission of rotation between contacting toothed wheels can be traced back to the Antikythera mechanism of Greece and the south-pointing chariot of China. Illustrations by the Renaissance scientist Georgius Agricola show gear trains with cylindrical teeth. The implementation of the involute tooth yielded

1632-436: A standard gear design that provides a constant speed ratio. The pitch circle of a given gear is determined by the tangent point contact between two meshing gears; for example, two spur gears mesh together when their pitch circles are tangent, as illustrated. The pitch diameter d {\displaystyle d} is the diameter of a gear's pitch circle, measured through that gear's rotational centerline, and

1728-462: 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

1824-440: Is an integer determined by the pitch circle and circular pitch. The circular pitch p {\displaystyle p} of a gear can be defined as the circumference of the pitch circle using its pitch radius r {\displaystyle r} divided by the number of teeth N {\displaystyle N} : The thickness t {\displaystyle t} of each tooth, measured through

1920-407: Is called an idler gear. Sometimes, a single idler gear is used to reverse the direction, in which case it may be referred to as a reverse idler . For instance, the typical automobile manual transmission engages reverse gear by means of inserting a reverse idler between two gears. Idler gears can also transmit rotation among distant shafts in situations where it would be impractical to simply make

2016-440: Is equivalently determined by the ratio of the number of teeth: In other words, the [angular] speed ratio is inversely proportional to the radius of the pitch circle and the number of teeth of gear A , and directly proportional to the same values for gear B . The gear ratio also determines the transmitted torque. The torque ratio T R A B {\displaystyle {\mathrm {TR} }_{AB}} of

SECTION 20

#1732786625081

2112-649: Is followed by a non-rotating stage of stator vanes. The two stages have variable pitch control. The RISE has a tractor configuration that pulls the aircraft into motion, unlike the pusher configuration of those other engines. The single-rotating design had previously been validated by the IRON project as part of the Clean Sky 2 program, and GE had dubbed the concept as the Unducted Single Fan (USF) engine. The fixed stator vanes vary their pitch to deswirl

2208-405: Is given by This shows that if the output gear B has more teeth than the input gear A , then the gear train amplifies the input torque. In this case, the gear train is called a speed reducer and since the output gear must have more teeth than the input gear, the speed reducer amplifies the input torque. When the input gear rotates faster than the output gear, then the gear train amplifies

2304-425: Is not connected directly to either the motor or the output shaft and only transmits power between the input and output gears. There is a third gear (Gear B ) partially shown in the upper-right corner of the photo. Assuming that gear is connected to the machine's output shaft, it is the output or driven gear. Considering only gears A and I , the gear ratio between the idler and the input gear can be calculated as if

2400-642: Is slated for certification as an "integrated engine" instead of a traditional "propeller/engine" because of its airframe integration complexity. 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. Turboprops have an optimum speed below about 450 mph (390 kn; 720 km/h), 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

2496-399: Is the gear ratio of the gear train, the input torque T A {\displaystyle T_{A}} applied to the input gear A and the output torque T B {\displaystyle T_{B}} on the output gear B are related by the same gear or speed ratio. The torque ratio of a gear train is also known as its mechanical advantage ; as demonstrated,

2592-459: Is the number of teeth on a gear divided by the pitch diameter; for SI countries, the module m {\displaystyle m} is the reciprocal of this value. For any gear, the relationship between the number of teeth, diametral pitch or module, and pitch diameter is given by: Since the pitch diameter is related to circular pitch as this means Rearranging, we obtain a relationship between diametral pitch and circular pitch: For

2688-566: The An-70 military transport aircraft, powered by four Progress D-27s attached to wings mounted to the top of the fuselage. 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. Since the propeller component of the Progress D-27 is made by Russia's SPE Aerosila , however, the An-70

2784-602: 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. When the 1973 oil crisis caused petroleum price spikes in the early 1970s, interest in propfans soared, and NASA-funded research began to accelerate. The propfan concept

2880-519: The CFM LEAP turbofan engine, with plans to enter service in the mid-2030s. At the 2022 Farnborough Airshow in July of that year, CFM International and Airbus announced plans to start flight tests for the RISE engine on an Airbus A380 -based testbed in 2026. In June 2023, General Electric tested the first rotating components of the new engine, mating the first high-speed, low-pressure turbine stage to

2976-493: 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

CFM International RISE - Misplaced Pages Continue

3072-645: 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

3168-731: 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, had a thrust rating of 9,000 lbf (40 kN). It was first operated in flight on March 28, 1987. The extensive test program, which cost about $ 56 million, racked up 73 flights and over 133 hours of flight time before finishing on March 25, 1988. In 1989, however,

3264-491: The pitch radius r {\displaystyle r} is the radius of the pitch circle. The distance between the rotational centerlines of two meshing gears is equal to the sum of their respective pitch radii. The circular pitch p {\displaystyle p} is the distance, measured along the pitch circle, between one tooth and the corresponding point on an adjacent tooth. The number of teeth N {\displaystyle N} per gear

3360-402: The testbed aircraft returned to the air from April 3 through April 14 to measure ground noise levels during flight. The engine was removed after that, and the aircraft was converted to a space shuttle training aircraft later that year. The GE36 Unducted Fan (UDF), from American engine maker General Electric (GE) with 35-percent participation from French partner Snecma (now Safran ),

3456-477: The #3 engine station of a Boeing 727-100 on August 20, 1986. 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), 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

3552-442: 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. 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

3648-538: The 1980s although it developed an open rotor design that was thought to be a finalist for the Irkut MS-21 narrowbody aircraft. 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 . The European Commission launched an Open Rotor demonstration in 2008 led by Safran within the Clean Sky program funded with €65 million over eight years. A demonstrator

3744-457: The 1991 Paris Air Show , as a demonstration for the planned Yak-46 aircraft with twin propfan engines, 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) (Mach 0.75). The Soviets claimed the D-236 had a true aerodynamic efficiency of 28 percent and

3840-500: 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. It unsuccessfully initiated discussions with Airbus, Boeing, and Rolls-Royce to produce the aircraft. 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), and

3936-584: The CFM56 family, and that " There is no point in spending more money on turbofans. UDF is the future." 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

CFM International RISE - Misplaced Pages Continue

4032-542: 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. 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

4128-408: 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

4224-697: The UDF's blade technology directly into the GE90 , the most powerful jet engine ever produced, for the Boeing 777 . 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

4320-722: The United States Federal Aviation Administration (FAA) Stage 4 regulations, which correspond to International Civil Aviation Organization (ICAO) Chapter 4 standards. A 2012 trade study projected that propfan noise would be 10–13 decibels quieter than allowed by Stage 4 regulations. Stage 5 noise limits reduce the limits by only seven effective perceived noise decibels ( EPNdB ), 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. Snecma claimed that its propfan engines would have about

4416-471: 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: Engine makers expect propfan implementations to meet community (as opposed to cabin) noise regulations without sacrificing

4512-437: The angular rotation of all the gears in the gear train are defined by the angle of the input gear. The input torque T A {\displaystyle T_{A}} acting on the input gear A is transformed by the gear train into the output torque T B {\displaystyle T_{B}} exerted by the output gear B . Let R A B {\displaystyle R_{AB}} be

4608-494: 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. Propfan blades had approximately half the thickness-to-chord ratio of the best conventional propeller blades of the era, thinned to razor-like sharpness at their edges, and weighed as little as 20 pounds (9.1 kg). (The GE36 UDF engine that

4704-458: 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. Safran's future open rotor engine, however, would have a maximum diameter of almost 14.8 ft (4.50 m; 177 in; 450 cm). In 2007, the Progress D-27 was successfully modified to meet

4800-433: The distant gears larger to bring them together. Not only do larger gears occupy more space, the mass and rotational inertia ( moment of inertia ) of a gear is proportional to the square of its radius. Instead of idler gears, a toothed belt or chain can be used to transmit torque over distance. If a simple gear train has three gears, such that the input gear A meshes with an intermediate gear I which in turn meshes with

4896-419: The drive gear ( A ) must make 1.62 revolutions to turn the output gear ( I ) once. It also means that for every one revolution of the driver ( A ), the output gear ( I ) has made 13 ⁄ 21 = 1 ⁄ 1.62 , or 0.62, revolutions. The larger gear ( I ) turns slower. The third gear in the picture ( B ) has N B = 42 {\displaystyle N_{B}=42} teeth. Now consider

SECTION 50

#1732786625081

4992-403: The driver and driven gear. If the driver gear moves in the clockwise direction, then the driven gear also moves in the clockwise direction with the help of the idler gear. In the photo, assume the smallest gear (Gear A , in the lower right corner) is connected to the motor, which makes it the drive gear or input gear. The somewhat larger gear in the middle (Gear I ) is called an idler gear. It

5088-600: 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. In 2007, the Progress D-27 was 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. A 2012 trade study projected that noise from existing open rotor technology would be 10–13 decibels quieter than

5184-401: 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

5280-575: The flow, and they close almost completely together to act as an air brake , avoiding the need for a thrust reverser . The RISE will also use a recuperator , which captures waste heat from the exhaust gas to pre-heat the air that exits the compressor before it enters the combustor . Related development Related lists Open rotor engine 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

5376-525: 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. 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

5472-403: The gear ratio and speed ratio of a gear train also give its mechanical advantage. The mechanical advantage M A {\displaystyle \mathrm {MA} } of a pair of meshing gears for which the input gear A has N A {\displaystyle N_{A}} teeth and the output gear B has N B {\displaystyle N_{B}} teeth

5568-412: The gear ratio for the subset consisting of gears I and B , with the idler gear I serving as the input and third gear B serving as the output. The gear ratio between the idler ( I ) and third gear ( B ) R I B {\displaystyle R_{IB}} is thus or 2:1. The final gear ratio of the compound system is 1.62×2≈3.23. For every 3.23 revolutions of the smallest gear A ,

5664-415: The gear ratios of the two subsets are multiplied: Notice that this gear ratio is exactly the same as for the case when the gears A and B engage directly. The intermediate gear provides spacing but does not affect the gear ratio. For this reason it is called an idler gear. The same gear ratio is obtained for a sequence of idler gears and hence an idler gear is used to provide the same direction to rotate

5760-424: The gear train is defined as the ratio of its output torque to its input torque. Using the principle of virtual work , the gear train's torque ratio is equal to the gear ratio, or speed ratio, of the gear train. Again, assume we have two gears A and B , with subscripts designating each gear and gear A serving as the input gear. For this analysis, consider a gear train that has one degree of freedom, which means

5856-524: The gear train. The speed ratio R A B {\displaystyle R_{AB}} of the gear train can be rearranged to give the magnitude of angular velocity of the output gear in terms of the input gear velocity. Rewriting in terms of a common angular velocity, The principle of virtual work states the input force on gear A and the output force on gear B using applied torques will sum to zero: This can be rearranged to: Since R A B {\displaystyle R_{AB}}

SECTION 60

#1732786625081

5952-641: The gear, so gear A has a radius of r A {\displaystyle r_{A}} and angular velocity of ω A {\displaystyle \omega _{A}} with N A {\displaystyle N_{A}} teeth, which meshes with gear B which has corresponding values for radius r B {\displaystyle r_{B}} , angular velocity ω B {\displaystyle \omega _{B}} , and N B {\displaystyle N_{B}} teeth. When these two gears are meshed and turn without slipping,

6048-458: The gears will come into contact with every tooth on the other gear before encountering the same tooth again. This results in less wear and longer life of the mechanical parts. A non-hunting gear set is one where the teeth counts are insufficiently prime. In this case, some particular gear teeth will come into contact with particular opposing gear teeth more times than others, resulting in more wear on some teeth than others. The simplest example of

6144-420: 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

6240-437: The idler gear was the output gear. The input gear A in this two-gear subset has 13 teeth ( N A {\displaystyle N_{A}} ) and the idler gear I has 21 teeth ( N I {\displaystyle N_{I}} ). Therefore, the gear ratio for this subset R A I {\displaystyle R_{AI}} is This is approximately 1.62 or 1.62:1. At this ratio, it means

6336-415: 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. Hamilton Standard, the only large American manufacturer of aircraft propellers, developed the propfan concept in the early 1970s. Hamilton Standard tested numerous variations in conjunction with NASA . Under

6432-564: 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

6528-468: The input torque. Conversely, if the output gear has fewer teeth than the input gear, then the gear train reduces the input torque; in other words, when the input gear rotates slower than the output gear, the gear train reduces the input torque. A hunting gear set is a set of gears where the gear teeth counts are relatively prime on each gear in an interfacing pair. Since the number of teeth on each gear have no common factors , then any tooth on one of

6624-793: The maximum noise level allowed by the Stage 4 regulations; 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 ), 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. Snecma , however, maintains that open-rotor tests show that its propfan engines would have about

6720-429: The maximum tip speed for the propeller blades of a conventional turbofan. That maximum blade tip speed would be kept constant despite wider or narrower propeller diameter (resulting in an RPM reduction or increase, respectively). 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,

6816-494: The output gear B , then the pitch circle of the intermediate gear rolls without slipping on both the pitch circles of the input and output gears. This yields the two relations The speed ratio of the overall gear train is obtained by multiplying these two equations for each pair ( A / I and I / B ) to obtain This is because the number of idler gear teeth N I {\displaystyle N_{I}} cancels out when

6912-474: The pitch circle, is equal to the gap between neighboring teeth (also measured through the pitch circle) to ensure the teeth on adjacent gears, cut to the same tooth profile, can mesh without interference. This means the circular pitch p {\displaystyle p} is equal to twice the thickness of a tooth, In the United States, the diametral pitch P {\displaystyle P}

7008-470: 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. Computer-aided design was also useful in refining blade characteristics. Since the blades bend and deflect with higher power loading and centrifugal force ,

7104-531: The propfan concept for jetliners beyond the Boeing 787 and Airbus A350 XWB. For instance, Airbus patented aircraft designs with twin rear-mounted contra-rotating propfans. 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 with 13,000 hp (9,700 kW) of shaft power. It became lukewarm on propfan technology in

7200-421: The ratio of the tooth counts. In a sequence of gears chained together, the ratio depends only on the number of teeth on the first and last gear. The intermediate gears, regardless of their size, do not alter the overall gear ratio of the chain. However, the addition of each intermediate gear reverses the direction of rotation of the final gear. An intermediate gear which does not drive a shaft to perform any work

7296-547: The rotational direction, to counter the twisting that is generated by the backward swept blade tips.) 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. 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), or about half

7392-445: 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). 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

7488-700: 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

7584-460: The same noise levels as its CFM LEAP turbofan engine, 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. In 2007,

7680-409: The same noise levels as its CFM LEAP turbofan engine. In 2021, CFM International 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

7776-428: The same tooth and gap widths, they also must have the same circular pitch p {\displaystyle p} , which means This equation can be rearranged to show the ratio of the pitch circle radii of two meshing gears is equal to the ratio of their number of teeth: Since the angular speed ratio R A B {\displaystyle R_{AB}} depends on the ratio of pitch circle radii, it

7872-401: The speed ratio, then by definition Assuming the gears are rigid and there are no losses in the engagement of the gear teeth, then the principle of virtual work can be used to analyze the static equilibrium of the gear train. Because there is a single degree of freedom, the angle θ of the input gear completely determines the angle of the output gear and serves as the generalized coordinate of

7968-473: The turbulent propwash adversely influencing the elevators and causing vibration issues therein. 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. If the propfans are mounted to

8064-527: The two CFM parent companies SAFRAN and GE Aviation (now GE Aerospace), and others. The 1973 oil crisis increased oil prices in the 1970s, which caused engine manufacturers to research new technologies to reduce fuel burn, including open rotor (also known as propfan) engines. However, none of those designs made it to production aircraft, mostly due to decreasing oil prices and concerns over the high noise footprint of those engines. Both Safran and GE Aviation had experimented with open rotor based engine designs in

8160-462: The velocity v {\displaystyle v} of the tangent point where the two pitch circles come in contact is the same on both gears, and is given by: Rearranging, the ratio of angular velocity magnitudes is the inverse of the ratio of pitch circle radii: Therefore, the angular speed ratio can be determined from the respective pitch radii: For example, if gear A has a pitch circle radius of 1 in (25 mm) and gear B has

8256-468: 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, although the overall installation issues still apply. Turboprops and most propfans are rated by the amount of shaft horsepower (shp) that they produce, as opposed to turbofans and

8352-677: The years before the RISE project was announced. Safran had performed ground tests for an open rotor engine in 2019 as a part of the European Union 's Clean Sky project, while GE had performed wind tunnel tests on a derivative of the GE36 engine at the start of the 2010s in collaboration with the Federal Aviation Administration . CFM International announced the RISE program in June 2021 as an intended successor of

8448-578: 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. The D-236 flew 36 times for a total of 70 flight test hours on the Il-76. 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-42 E-LL and flown to

8544-401: Was a pair of contra-rotating rows. Airframers, who had been wary of issue-prone gearboxes since the 1950s, liked GE's gearless version of the propfan: Boeing intended to offer GE's pusher UDF engine on the 7J7 platform (which would have had a cruise speed of Mach 0.83), and McDonnell Douglas planned to do likewise on their MD-94X airliner . The GE36 was first flight tested mounted on

8640-451: 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

8736-619: 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 CO 2 emissions by 30% compared with current CFM56 turbofans. After the completion of ground testing at the end of 2017, Safran's geared open rotor engine had reached technology readiness level 5. 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

8832-477: 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

8928-655: 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. Other announcements of future propfan-powered airliners included: None of these projects came to fruition, however, mainly because of excessive cabin noise (compared to turbofans) and low fuel prices. For General Electric,

9024-431: Was outlined by Carl Rohrbach and Bruce Metzger of the Hamilton Standard division of United Technologies in 1975 and was patented by Rohrbach and Robert Cornell of Hamilton Standard in 1979. 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,

9120-476: Was stymied by the Russo-Ukrainian War . Antonov began working instead 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. 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

9216-485: 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.) 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

#80919