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120-476: The CFM International CFM56 (U.S. military designation F108 ) series is a Franco-American family of high-bypass turbofan aircraft engines made by CFM International (CFMI), with a thrust range of 18,500 to 34,000  lbf (82 to 150  kN ). CFMI is a 50–50 joint-owned company of Safran Aircraft Engines (formerly known as Snecma) of France, and GE Aerospace (GE) of the United States. GE produces

240-594: A "Thrust Management System". After testing the engine for several years, both in the air and on the ground, CFMI searched for customers outside of a possible AMST contract. The main targets were re-engine contracts for the Douglas DC-8 and the Boeing 707 airliners, including the related military tanker, the KC-135 Stratotanker . There was little initial interest in the engine, but Boeing realized that

360-423: A CFM56-7B engine demonstrated an improvement of 46% over single-annular combustors and 22% over double-annular combustors. The analytical tools developed for TAPS have also been used to improve other combustors, notably the single-annular combustors in some CFM56-5B and -7B engines. The high-pressure compressor (HPC), that was at the center of the original export controversy, features nine stages in all variants of

480-434: A corresponding increase in pressure and temperature in the exhaust duct which in turn cause a higher gas speed from the propelling nozzle (and higher KE and wasted fuel). Although the engine would use less fuel to produce a pound of thrust, more fuel is wasted in the faster propelling jet. In other words, the independence of thermal and propulsive efficiencies, as exists with the piston engine/propeller combination which preceded

600-419: A discordant nature known as "buzz saw" noise. All modern turbofan engines have acoustic liners in the nacelle to damp their noise. They extend as much as possible to cover the largest surface area. The acoustic performance of the engine can be experimentally evaluated by means of ground tests or in dedicated experimental test rigs. In the aerospace industry, chevrons are the "saw-tooth" patterns on

720-410: A fixed total applied fuel:air ratio, the total fuel flow for a given fan airflow will be the same, regardless of the dry specific thrust of the engine. However, a high specific thrust turbofan will, by definition, have a higher nozzle pressure ratio, resulting in a higher afterburning net thrust and, therefore, a lower afterburning specific fuel consumption (SFC). However, high specific thrust engines have

840-426: A high dry SFC. The situation is reversed for a medium specific thrust afterburning turbofan: i.e., poor afterburning SFC/good dry SFC. The former engine is suitable for a combat aircraft which must remain in afterburning combat for a fairly long period, but has to fight only fairly close to the airfield (e.g. cross border skirmishes). The latter engine is better for an aircraft that has to fly some distance, or loiter for

960-416: A higher nozzle pressure ratio than the turbojet, but with a lower exhaust temperature to retain net thrust. Since the temperature rise across the whole engine (intake to nozzle) would be lower, the (dry power) fuel flow would also be reduced, resulting in a better specific fuel consumption (SFC). Some low-bypass ratio military turbofans (e.g. F404 , JT8D ) have variable inlet guide vanes to direct air onto

1080-590: A long time, before going into combat. However, the pilot can afford to stay in afterburning only for a short period, before aircraft fuel reserves become dangerously low. The first production afterburning turbofan engine was the Pratt & Whitney TF30 , which initially powered the F-111 Aardvark and F-14 Tomcat . Low-bypass military turbofans include the Pratt & Whitney F119 , the Eurojet EJ200 ,

1200-418: A new, double-annular combustor. Instead of having just one combustion zone, the double-annular combustor has a second combustion zone that is used at high thrust levels. This design lowers the emissions of both nitrogen oxides (NO x ) and carbon dioxide (CO 2 ). The first CFM56 engine with the double-annular combustor entered service in 1995, and the combustor is used on CFM56-5B and CFM56-7B variants with

1320-476: A part of their "Tech Insertion" management plan from 2007. CFMI tested both a mixed and unmixed exhaust design at the beginning of development; most variants of the engine have an unmixed exhaust nozzle. Only the high-power CFM56-5C, designed for the Airbus A340, has a mixed-flow exhaust nozzle. GE and Snecma also tested the effectiveness of chevrons on reducing jet noise. After examining configurations in

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1440-403: A pure-jet of the same thrust, and jet noise is no longer the predominant source. Turbofan engine noise propagates both upstream via the inlet and downstream via the primary nozzle and the by-pass duct. Other noise sources are the fan, compressor and turbine. Modern commercial aircraft employ high-bypass-ratio (HBPR) engines with separate flow, non-mixing, short-duct exhaust systems. Their noise

1560-569: A static thrust of 4,320 lb (1,960 kg), and had a bypass ratio of 6:1. The General Electric TF39 became the first production model, designed to power the Lockheed C-5 Galaxy military transport aircraft. The civil General Electric CF6 engine used a derived design. Other high-bypass turbofans are the Pratt & Whitney JT9D , the three-shaft Rolls-Royce RB211 and the CFM International CFM56 ; also

1680-473: A turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A bypass ratio of 6, for example, means that 6 times more air passes through the bypass duct than the amount that passes through the combustion chamber. Turbofan engines are usually described in terms of BPR, which together with overall pressure ratio, turbine inlet temperature and fan pressure ratio are important design parameters. In addition BPR

1800-421: A turbojet engine uses all of the engine's output to produce thrust in the form of a hot high-velocity exhaust gas jet, a turbofan's cool low-velocity bypass air yields between 30% and 70% of the total thrust produced by a turbofan system. The thrust ( F N ) generated by a turbofan depends on the effective exhaust velocity of the total exhaust, as with any jet engine, but because two exhaust jets are present

1920-496: A turbojet even though an extra turbine, a gearbox and a propeller are added to the turbojet's low-loss propelling nozzle. The turbofan has additional losses from its greater number of compressor stages/blades, fan and bypass duct. Froude, or propulsive, efficiency can be defined as: η f = 2 1 + V j V a {\displaystyle \eta _{f}={\frac {2}{1+{\frac {V_{j}}{V_{a}}}}}} where: While

2040-704: A turbojet which accelerates a smaller amount more quickly, which is a less efficient way to generate the same thrust (see the efficiency section below). The ratio of the mass-flow of air bypassing the engine core compared to the mass-flow of air passing through the core is referred to as the bypass ratio . Engines with more jet thrust relative to fan thrust are known as low-bypass turbofans , those that have considerably more fan thrust than jet thrust are known as high-bypass . Most commercial aviation jet engines in use are high-bypass, and most modern fighter engines are low-bypass. Afterburners are used on low-bypass turbofans on combat aircraft. The bypass ratio (BPR) of

2160-462: Is a new engine design based on and designed to replace the CFM56 series, with 16% efficiency savings by using more composite materials and achieving higher bypass ratios of over 10:1. LEAP entered service in 2016. As of June 2016, the CFM56 is the most-used high-bypass turbofan . It has achieved more than 800 million engine flight hours, and at a rate of one million flight hours every eight days it

2280-408: Is also commonly called the "low-pressure compressor" (LPC) as it is part of the low-pressure spool and continues the air compression done by the inner part of the fan before it reaches the high-pressure compressor. The original CFM56-2 variant featured 44 tip-shrouded fan blades, although the number of fan blades was reduced in later variants as wide-chord blade technology developed, down to 22 blades in

2400-713: Is an afterburning turbofan jet engine . It powers the Rockwell B-1 Lancer strategic bomber fleet of the USAF . In full afterburner it produces a thrust of more than 30,000 pounds-force (130  kN ). The F101 was GE 's first turbofan with an afterburner. The F101 was developed specifically for the Advanced Manned Strategic Aircraft, which became the B-1A. The F101 powered the four development aircraft from 1970 to 1981. The B-1A

2520-507: Is best suited to high supersonic speeds. If it is all transferred to a separate big mass of air with low kinetic energy, the aircraft is best suited to zero speed (hovering). For speeds in between, the gas power is shared between a separate airstream and the gas turbine's own nozzle flow in a proportion which gives the aircraft performance required. The trade off between mass flow and velocity is also seen with propellers and helicopter rotors by comparing disc loading and power loading. For example,

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2640-410: Is considerable potential for reducing fuel consumption for the same core cycle by increasing BPR.This is achieved because of the reduction in pounds of thrust per lb/sec of airflow (specific thrust) and the resultant reduction in lost kinetic energy in the jets (increase in propulsive efficiency). If all the gas power from a gas turbine is converted to kinetic energy in a propelling nozzle, the aircraft

2760-430: Is due to the speed, temperature, and pressure of the exhaust jet, especially during high-thrust conditions, such as those required for takeoff. The primary source of jet noise is the turbulent mixing of shear layers in the engine's exhaust. These shear layers contain instabilities that lead to highly turbulent vortices that generate the pressure fluctuations responsible for sound. To reduce the noise associated with jet flow,

2880-409: Is expected to have achieved one billion flight hours by 2020. It has more than 550 operators and more than 2,400 CFM56-powered jet aircraft are in the air at any given moment. It is known for its dependability : its average time on wing is 30,000 hours before a first shop visit , with the current fleet record at 50,000 hours. As of July 2016, 30,000 engines have been built: 9,860 CFM56-5 engines for

3000-413: Is quoted for turboprop and unducted fan installations because their high propulsive efficiency gives them the overall efficiency characteristics of very high bypass turbofans. This allows them to be shown together with turbofans on plots which show trends of reducing specific fuel consumption (SFC) with increasing BPR. BPR can also be quoted for lift fan installations where the fan airflow is remote from

3120-538: Is referred to as the bypass ratio . The engine produces thrust through a combination of these two portions working together. Engines that use more jet thrust relative to fan thrust are known as low-bypass turbofans ; conversely those that have considerably more fan thrust than jet thrust are known as high-bypass . Most commercial aviation jet engines in use are of the high-bypass type, and most modern fighter engines are low-bypass. Afterburners are used on low-bypass turbofan engines with bypass and core mixing before

3240-415: Is separate, and a cannular combustor which is a hybrid of the two. Fuel injection is regulated by a hydromechanical unit (HMU) built by Honeywell . It regulates the amount of fuel delivered to the engine by means of an electrohydraulic servo valve that, in turn, drives a fuel metering valve, that provides information to the full authority digital engine controller ( FADEC ). In 1989, CFMI began work on

3360-420: Is sufficient core power to drive the fan. A smaller core flow/higher bypass ratio cycle can be achieved by raising the inlet temperature of the high-pressure (HP) turbine rotor. To illustrate one aspect of how a turbofan differs from a turbojet, comparisons can be made at the same airflow (to keep a common intake for example) and the same net thrust (i.e. same specific thrust). A bypass flow can be added only if

3480-411: Is very fuel intensive. Consequently, afterburning can be used only for short portions of a mission. Unlike in the main engine, where stoichiometric temperatures in the combustor have to be reduced before they reach the turbine, an afterburner at maximum fuelling is designed to produce stoichiometric temperatures at entry to the nozzle, about 2,100 K (3,800 °R; 3,300 °F; 1,800 °C). At

3600-475: The Airbus A300 . Pratt & Whitney was considering upgrading their JT8D to compete in the same class as the CFM56 as a sole venture, while Rolls-Royce dealt with financial issues that precluded them from starting new projects; this situation caused GE to gain the title of best partner for the program. A major reason for GE's interest in the collaboration, rather than building a 10-ton engine on their own,

3720-859: The Airbus A320ceo and A340 -200/300 and more than 17,300 CFM56-3/-7B engines for the Boeing 737 Classic and 737NG . In July 2016, CFM had 3,000 engines in backlog. Lufthansa , launch customer for the CFM56-5C-powered A340, have an engine with more than 100,000 flight hours, having entered commercial service on 16 November 1993, overhauled four times since. In 2016 CFM delivered 1,665 CFM56 and booked 876 orders, it plans to produce CFM56 spare parts until 2045. By October 2017, CFM had delivered more than 31,000 engines and 24,000 were in service with 560 operators, it attained 500 million flight cycles and 900 million flight hours, including over 170 million cycles and 300 million hours since 1998 for

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3840-479: The Bristol Olympus , and Pratt & Whitney JT3C engines, increased the overall pressure ratio and thus the thermodynamic efficiency of engines. They also had poor propulsive efficiency, because pure turbojets have a high specific thrust/high velocity exhaust, which is better suited to supersonic flight. The original low-bypass turbofan engines were designed to improve propulsive efficiency by reducing

3960-702: The General Electric F110 , the Klimov RD-33 , and the Saturn AL-31 , all of which feature a mixed exhaust, afterburner and variable area propelling nozzle. To further improve fuel economy and reduce noise, almost all jet airliners and most military transport aircraft (e.g., the C-17 ) are powered by low-specific-thrust/high-bypass-ratio turbofans. These engines evolved from the high-specific-thrust/low-bypass-ratio turbofans used in such aircraft in

4080-681: The KC-135 , the E-6 Mercury and some E-3 Sentry aircraft. The CFM56-2 comprises a single-stage fan with 44 blades, with a three-stage LP compressor driven by a four-stage LP turbine, and a nine-stage HP compressor driven by a single-stage HP turbine. The combustor is annular. The first derivative of the CFM56 series, the CFM56-3 was designed for Boeing 737 Classic series (737-300/-400/-500), with static thrust ratings from 18,500 to 23,500 lbf (82.3 to 105 kN). A "cropped fan" derivative of

4200-656: The McDonnell Douglas YC-15 , an entrant in the Air Force's Advanced Medium STOL Transport (AMST) competition. Soon after, the second CFM56 was mounted on a Sud Aviation Caravelle at the Snecma flight test center in France. This engine had a slightly different configuration with a long bypass duct and mixed exhaust flow, rather than a short bypass duct with unmixed exhaust flow. It was the first to include

4320-853: The United States Navy selected the CFM56-2 to power their variant of the Boeing ;707, the E-6 Mercury , in 1982. In 1984 the Royal Saudi Air Force selected the CFM56-2 to power their E-3 Sentry aircraft (also related to the 707 airframe ). The CFM56-2-powered E-3 also became the standard configuration for aircraft purchased by the British and French. By the end of the 1970s, airlines were considering upgrading their aging Douglas DC-8 aircraft as an alternative to buying new quieter and more efficient aircraft. Following

4440-485: The wind tunnel , CFMI chose to flight-test chevrons built into the core exhaust nozzle. The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions, and are now offered as an option with the CFM56 for the Airbus A321 . The CFM56 features a single-stage fan, and most variants have a three-stage booster on the low-pressure shaft, with four stages in the -5B and -5C variants. The booster

4560-515: The "10-ton" (20,000 lbf; 89 kN) thrust class, began in the late 1960s. Snecma (now Safran), who had mostly built military engines previously, was the first company to seek entrance into the market by searching for a partner with commercial experience to design and build an engine in this class. They considered Pratt & Whitney , Rolls-Royce , and GE Aviation as potential partners, and after two company executives, Gerhard Neumann from GE and René Ravaud from Snecma, introduced themselves at

4680-401: The "Tech56" development and demonstration program to create an engine for the new single-aisle aircraft that were expected to be built by Airbus and Boeing. The program focused on developing a large number of new technologies for the theoretical future engine, not necessarily creating an all-new design. When it became clear that Boeing and Airbus were not going to build all-new aircraft to replace

4800-403: The -2, the -3 engine has a smaller fan diameter at 60 in (1.5 m) but retains the original basic engine layout. The new fan was primarily derived from GE's CF6-80 turbofan rather than the CFM56-2, and the booster was redesigned to match the new fan. High-bypass turbofan The ratio of the mass-flow of air bypassing the engine core to the mass-flow of air passing through the core

4920-404: The 10-ton engine, the CFM56. The venture was officially founded in 1974. The "CF" in the engine name stands for GE's designation for commercial turbofan engines, while the "M56" is the name of Snecma's original engine proposal. The two primary roles for CFMI were to manage the program between GE and Snecma, and to market, sell and service the engine at a single point of contact for the customer. CFMI

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5040-421: The 1960s. Modern combat aircraft tend to use low-bypass ratio turbofans, and some military transport aircraft use turboprops . Low specific thrust is achieved by replacing the multi-stage fan with a single-stage unit. Unlike some military engines, modern civil turbofans lack stationary inlet guide vanes in front of the fan rotor. The fan is scaled to achieve the desired net thrust. The core (or gas generator) of

5160-458: The 1971 Paris Air Show a decision was made. The two companies saw mutual benefit in the collaboration and met several more times, fleshing out the basics of the joint project. At the time, Pratt & Whitney dominated the commercial market. GE needed an engine in this market class, and Snecma had previous experience of working with them, collaborating on the production of the CF6-50 turbofan for

5280-648: The 737 and A320, CFMI decided to apply some of those Tech56 technologies to the CFM56 in the form of the "Tech Insertion" program which focused on three areas: fuel efficiency , maintenance costs and emissions. Launched in 2004, the package included redesigned high-pressure compressor blades, an improved combustor, and improved high- and low-pressure turbine components which resulted in better fuel efficiency and lower nitrogen oxides (NO x ) emissions. The new components also reduced engine wear, lowering maintenance costs by about 5%. The engines entered service in 2007, and all new CFM56-5B and CFM56-7B engines are being built with

5400-527: The B737NG's -7B and over 100 million cycles and 180 million hours for the A320ceo's -5B since 1996. By June 2018, 32,645 were delivered. Strong demand will extend production to 2020, up from 2019. Exhaust gas temperature margin erodes with usage. One or two performance restoration shop visits, costing $ 0.3-$ 0.6m for a -5 series, can be performed before taking the engine off wing, which can restore 60% to 80% of

5520-411: The CFM56 a firm footing in both the military and commercial market. In the early 1980s Boeing selected the CFM56-3 to exclusively power the Boeing 737-300 variant. The 737 wings were closer to the ground than previous applications for the CFM56, necessitating several modifications to the engine. The fan diameter was reduced, which reduced the bypass ratio, and the engine accessory gearbox was moved from

5640-414: The CFM56 began before CFMI was formally created. While work proceeded smoothly, the international arrangement led to unique working conditions. For example, both companies had assembly lines, some engines were assembled and tested in the U.S. and others in France. Engines assembled in France were subject to the initially strict export agreement, which meant that GE's core was built in the U.S., then shipped to

5760-423: The CFM56 might be a solution to upcoming noise regulations. After announcing that a 707 would be configured with the CFM56 engine for flight tests in 1977, Boeing officially offered the 707-320 with the CFM56 engine as an option in 1978. The new variant was listed as the 707-700. Due to limited interest from the airlines in a re-engined 707, Boeing ended the 707-700 program in 1980 without selling any aircraft. Despite

5880-406: The CFM56, and that change has a direct impact on the engine performance. For example, the low-pressure shaft rotates at the same speed for both the CFM56-2 and the CFM56-3 models; the fan diameter is smaller on the -3, which lowers the tip speed of the fan blades. The lower speed allows the fan blades to operate more efficiently (5.5% more in this case), which increases the overall fuel efficiency of

6000-475: The CFM56-7 variant. The CFM56 fan features dovetailed fan blades which allows them to be replaced without removing the entire engine, and GE/Snecma claim that the CFM56 was the first engine to have that capability. This attachment method is useful for circumstances where only a few fan blades need to be repaired or replaced, such as following bird strikes . The fan diameter varies with the different models of

6120-501: The CFM56. However, the CFM56 was not without its own issues; several fan blade failure incidents were experienced during early service, including one failure that was a cause of the Kegworth air disaster , and some CFM56 variants experienced problems when flying through rain or hail. Both of these issues were resolved with engine modifications. Research into the next generation of commercial jet engines, high-bypass ratio turbofans in

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6240-496: The CFM56. The compressor stages have been developed from GE 's "GE core " (namely a single-turbine, nine-compressor stage design) which was designed in a compact core rotor. The small span of the compressor radius meant that the entire engine could be lighter and smaller, as the accessory units in the system ( bearings , oiling systems ) could be merged to the main fueling system running on aviation fuel. As design evolved HPC design improved through better airfoil design. As part of

6360-503: The F101 core technology. GE applied for the export license in 1972 as their primary contribution to the 10-ton engine project. The United States Department of State 's Office of Munitions Control recommended the rejection of the application on national security grounds; specifically because the core technology was an aspect of a strategic national defense system (B-1 bomber), it was built with Department of Defense funding, and that exporting

6480-572: The French KC-135 order in 1978, the April 1979 decision by United Airlines to upgrade 30 of their DC-8-61 aircraft with the CFM56-2 was important for securing the development of the CFM56; GE and Snecma were two weeks away from freezing development had that order not materialized. This decision marked the first commercial purchase (rather than government/military) of the engine, and Delta Air Lines and Flying Tiger Line soon followed suit, giving

6600-514: The Snecma plant in France where it was placed in a locked room into which even the President of Snecma was not allowed. The Snecma components (the fore and aft sections of the engine) were brought into the room, GE employees mounted them to the core, and then the assembled engine was taken out to be finished. The first completed CFM56 engine first ran at GE plant in Evendale on 20 June 1974 with

6720-515: The Tech Insertion components. CFMI also offers the components as an upgrade kit for existing engines. In 2009, CFMI announced the latest upgrade to the CFM56 engine, the "CFM56-7B Evolution" or CFM56-7BE. This upgrade, announced with improvements to Boeing's 737 Next Generation, further enhances the high- and low-pressure turbines with better aerodynamics, as well as improving engine cooling, and aims to reduce overall part count. CFMI expected

6840-504: The Tech-56 improvement program CFMI has tested the new CFM-56 model with six-stage high-pressure compressor stages (discs that make up the compressor system) that was designed to deliver same pressure ratios (pressure gain 30) similar to the old nine-stages compressor design. The new one was not fully replacing the old one, but it offered an upgrade in HPC, thanks to improved blade dynamics, as

6960-464: The aerospace industry has sought to disrupt shear layer turbulence and reduce the overall noise produced. Fan noise may come from the interaction of the fan-blade wakes with the pressure field of the downstream fan-exit stator vanes. It may be minimized by adequate axial spacing between blade trailing edge and stator entrance. At high engine speeds, as at takeoff, shock waves from the supersonic fan tips, because of their unequal nature, produce noise of

7080-422: The afterburner, raising the temperature of exhaust gases by a significant degree, resulting in a higher exhaust velocity/engine specific thrust. The variable geometry nozzle must open to a larger throat area to accommodate the extra volume and increased flow rate when the afterburner is lit. Afterburning is often designed to give a significant thrust boost for take off, transonic acceleration and combat maneuvers, but

7200-409: The afterburner. Modern turbofans have either a large single-stage fan or a smaller fan with several stages. An early configuration combined a low-pressure turbine and fan in a single rear-mounted unit. The turbofan was invented to improve the fuel consumption of the turbojet. It achieves this by pushing more air, thus increasing the mass and lowering the speed of the propelling jet compared to that of

7320-474: The average stage loading and to maintain LP turbine efficiency. Reducing core flow also increases bypass ratio. Bypass ratios greater than 5:1 are increasingly common; the Pratt & Whitney PW1000G , which entered commercial service in 2016, attains 12.5:1. Further improvements in core thermal efficiency can be achieved by raising the overall pressure ratio of the core. Improvements in blade aerodynamics can reduce

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7440-610: The beginning of the end of American aerospace leadership. There was also speculation that the rejection may have been, in part, retaliation for French involvement in convincing the Swiss not to purchase American-made LTV A-7 Corsair II aircraft that had been competing against a French design, the Dassault Milan . In the end, the Swiss did not purchase either aircraft, opting for the Northrop F-5 E Tiger II instead. Despite

7560-426: The booster (low-pressure compressor) evolved over the different iterations of the engine, as did the compressor, combustor and turbine sections. Most variants of the CFM56 feature a single-annular combustor . An annular combustor is a continuous ring where fuel is injected into the airflow and ignited, raising the pressure and temperature of the flow. This contrasts with a can combustor , where each combustion chamber

7680-481: The bottom of the engine (the 6 o'clock position) to the 9 o'clock position, giving the engine nacelle its distinctive flat-bottomed shape. The overall thrust was also reduced, from 24,000 to 20,000 lbf (107 to 89 kN), mostly due to the reduction in bypass ratio. Since the small initial launch order for twenty 737-300s split between two airlines, over 5,000 Boeing 737 aircraft had been delivered with CFM56 turbofans by April 2010. In 1998, CFMI launched

7800-529: The bypass air flow. The blocked bypass air is forced through the cascades, reducing the thrust of the engine and slowing the aircraft down. The CFM56 also supports pivoting-door type thrust reversers. This type is used on the CFM56-5 engines that power many Airbus aircraft such as the Airbus A320. They work by actuating a door that pivots down into the bypass duct, both blocking the bypass air and deflecting

7920-762: The changes to result in a 4% reduction in maintenance costs and a 1% improvement in fuel consumption (2% improvement including the airframe changes for the new 737); flight and ground tests completed in May 2010 revealed that the fuel burn improvement was better than expected at 1.6%. Following 450 hours of testing, the CFM56-7BE engine was certified by FAA and EASA on 30 July 2010 and delivered from mid-2011. The CFM56-5B/3 PIP (Performance Improvement Package) engine includes these new technologies and hardware changes to lower fuel burn and lower maintenance cost. Airbus A320s were to use this engine version starting in late 2011. The LEAP

8040-514: The development money provided by the government for the F101 engine core. Documents declassified in 2007 revealed that a key aspect of the CFM56 export agreement was that the French government agreed not to seek tariffs against American aircraft being imported into Europe. With the export issue settled, GE and Snecma finalized the agreement that formed CFM International (CFMI), a 50–50 joint company that would be responsible for producing and marketing

8160-453: The development of a 10-ton engine – either to build a "limited" technology 10-ton engine with Snecma, or a similar engine with "advanced" technology on their own. Concerned that the company would be left with only the "limited" engine in its portfolio if it did not win the Air Force contract (for which it was competing with Pratt & Whitney and a General Motors division with its "advanced" engine), GE decided to apply for an export license for

8280-453: The development of the CFM56 to proceed. Contemporary reports state that the agreement was based on assurances that the core of the engine, the part that GE was developing from the military F101, would be built in the U.S. and then transported to France in order to protect the sensitive technologies. The joint venture also agreed to pay the U.S. an $ 80 million royalty fee (calculated at $ 20,000 per engine predicted to be built) as repayment for

8400-417: The engine (improving specific fuel consumption nearly 3%). The CFM56 is designed to support several thrust reverser systems which help slow and stop the aircraft after landing. The variants built for the Boeing 737, the CFM56-3 and the CFM56-7, use a cascade type of thrust reverser. This type of thrust reverse consists of sleeves that slide back to expose mesh-like cascades and blocker doors that block

8520-448: The engine and doesn't flow past the engine core. Considering a constant core (i.e. fixed pressure ratio and turbine inlet temperature), core and bypass jet velocities equal and a particular flight condition (i.e. Mach number and altitude) the fuel consumption per lb of thrust (sfc) decreases with increase in BPR. At the same time gross and net thrusts increase, but by different amounts. There

8640-506: The engine and is exhausted out of the fan case) with several variants having bypass ratios ranging from 5:1 to 6:1, generating 18,500 to 34,000 lbf (80 kN to 150 kN) of thrust. The variants share a common design, and differ only in details. The CFM56 is a two-shaft (or two-spool) engine, meaning that there are two rotating shafts, one high-pressure and one low-pressure. Each is powered by its own turbine section (the high-pressure and low-pressure turbines, respectively). The fan and

8760-427: The engine must generate enough power to drive the fan at its rated mass flow and pressure ratio. Improvements in turbine cooling/material technology allow for a higher (HP) turbine rotor inlet temperature, which allows a smaller (and lighter) core, potentially improving the core thermal efficiency. Reducing the core mass flow tends to increase the load on the LP turbine, so this unit may require additional stages to reduce

8880-524: The exhaust velocity to a value closer to that of the aircraft. The Rolls-Royce Conway , the world's first production turbofan, had a bypass ratio of 0.3, similar to the modern General Electric F404 fighter engine. Civilian turbofan engines of the 1960s, such as the Pratt & Whitney JT8D and the Rolls-Royce Spey , had bypass ratios closer to 1 and were similar to their military equivalents. The first Soviet airliner powered by turbofan engines

9000-529: The export license being rejected, both the French and GE continued to push the Nixon Administration for permission to export the F101 technology. Efforts continued throughout the months following the rejection, culminating in the engine becoming an agenda topic during the 1973 meeting of Presidents Nixon and Pompidou in Reykjavík . Discussions at this meeting resulted in an agreement that allowed

9120-494: The fan nozzle. The amount of energy transferred depends on how much pressure rise the fan is designed to produce (fan pressure ratio). The best energy exchange (lowest fuel consumption) between the two flows, and how the jet velocities compare, depends on how efficiently the transfer takes place which depends on the losses in the fan-turbine and fan. The fan flow has lower exhaust velocity, giving much more thrust per unit energy (lower specific thrust ). Both airstreams contribute to

9240-450: The first fan rotor stage. This improves the fan surge margin (see compressor map ). Since the 1970s, most jet fighter engines have been low/medium bypass turbofans with a mixed exhaust, afterburner and variable area exit nozzle. An afterburner is a combustor located downstream of the turbine blades and directly upstream of the nozzle, which burns fuel from afterburner-specific fuel injectors. When lit, large volumes of fuel are burnt in

9360-524: The flow outward, creating the reverse thrust. All variants of the CFM56 feature a single-stage high-pressure turbine (HPT). In some variants, the HPT blades are "grown" from a single crystal superalloy, giving them high strength and creep resistance. The low-pressure turbine (LPT) features four stages in most variants of the engine, but the CFM56-5C has a five-stage LPT. This change was implemented to drive

9480-496: The fuel used to move the aircraft forwards. A turbofan harvests that wasted velocity and uses it to power a ducted fan that blows air in bypass channels around the rest of the turbine. This reduces the speed of the propelling jet while pushing more air, and thus more mass. The other penalty is that combustion is less efficient at lower speeds. Any action to reduce the fuel consumption of the engine by increasing its pressure ratio or turbine temperature to achieve better combustion causes

9600-429: The gross thrust of the engine. The additional air for the bypass stream increases the ram drag in the air intake stream-tube, but there is still a significant increase in net thrust. The overall effective exhaust velocity of the two exhaust jets can be made closer to a normal subsonic aircraft's flight speed and gets closer to the ideal Froude efficiency . A turbofan accelerates a larger mass of air more slowly, compared to

9720-574: The high-pressure compressor , combustor , and high-pressure turbine , Safran manufactures the fan, gearbox , exhaust and the low-pressure turbine, and some components are made by Avio of Italy and Honeywell from the US. Both companies have their own final assembly line, GE in Evendale, Ohio , and Safran in Villaroche , France. The engine initially had extremely slow sales but has gone on to become

9840-474: The hot nozzle to convert to kinetic energy. Turbofans represent an intermediate stage between turbojets , which derive all their thrust from exhaust gases, and turbo-props which derive minimal thrust from exhaust gases (typically 10% or less). Extracting shaft power and transferring it to a bypass stream introduces extra losses which are more than made up by the improved propulsive efficiency. The turboprop at its best flight speed gives significant fuel savings over

9960-614: The lack of sales, having the commercial 707 available with the CFM56 helped the engine's competitiveness for the KC-135 re-engine contract. Winning the contract to re-engine the KC-135 tanker fleet for the USAF would be a huge boon to the CFM56 project (with more than 600 aircraft available to re-engine), and CFMI aggressively pursued that goal as soon as the Request For Proposals (RFP) was announced in 1977. Like other aspects of

10080-482: The larger fan on this variant. Improvements to the turbine section were examined during the Tech56 program, and one development was an aerodynamically optimized low-pressure turbine blade design, which would have used 20% fewer blades for the whole low-pressure turbine, saving weight. Some of those Tech56 improvements made their way into the Tech Insertion package, where the turbine section was updated. The turbine section

10200-417: The mechanical power produced by the turbine. In a bypass design, extra turbines drive a ducted fan that accelerates air rearward from the front of the engine. In a high-bypass design, the ducted fan and nozzle produce most of the thrust. Turbofans are closely related to turboprops in principle because both transfer some of the gas turbine's gas power, using extra machinery, to a bypass stream leaving less for

10320-494: The most used turbofan aircraft engine in the world. The CFM56 first ran in 1974. By April 1979, the joint venture had not received a single order in five years and was two weeks away from being dissolved. The program was saved when Delta Air Lines , United Airlines , and Flying Tigers chose the CFM56 to re-engine their Douglas DC-8 aircraft as part of the Super 70 program. The first engines entered service in 1982. The CFM56

10440-539: The number of extra compressor stages required, and variable geometry stators enable high-pressure-ratio compressors to work surge-free at all throttle settings. The first (experimental) high-bypass turbofan engine was the AVCO-Lycoming PLF1A-2, a Honeywell T55 turboshaft-derived engine that was first run in February 1962. The PLF1A-2 had a 40 in diameter (100 cm) geared fan stage, produced

10560-513: The original margin. Once restored, the life limited parts must be replaced after: 20,000 cycles for the hot section ($ 0.5m), 25,000 for the axial compressor , and 30,000 for the fan and booster ($ 0.5m-$ 0.7m) for a recent CFM56. The whole engine parts cost more than $ 3m, $ 3.5 to $ 4m with the shop work-hours, around $ 150 per cycle. By June 2019, the CFM56 fleet had surpassed one billion engine flight hours (nearly 115,000 years), having carried more than 35 billion people, over eight million times around

10680-404: The program, international politics played their part in this contract. In efforts to boost the CFM56's chances versus its competitors, the Pratt & Whitney TF33 and an updated Pratt & Whitney JT8D , the French government announced in 1978 that they would upgrade their 11 KC-135s with the CFM56, providing one of the first orders for the engine. The USAF announced the CFM56 as the winner of

10800-781: The re-engine contract in January 1980. Officials indicated that they were excited at the prospect of replacing the Pratt & Whitney J57 engines currently flying on the KC-135A aircraft, calling them "...the noisiest, dirtiest, [and] most fuel inefficient powerplant still flying" at the time. The re-engined aircraft was designated the KC-135R. The CFM56 brought many benefits to the KC-135, decreasing takeoff distance by as much as 3,500 ft (1,100 m), decreasing overall fuel usage by 25%, greatly reducing noise (24 dB lower) and lowering total life cycle cost. With those benefits in mind,

10920-467: The required thrust still maintained by increasing the mass accelerated. A turbofan does this by transferring energy available inside the engine, from the gas generator, to a ducted fan which produces a second, additional mass of accelerated air. The transfer of energy from the core to bypass air results in lower pressure and temperature gas entering the core nozzle (lower exhaust velocity), and fan-produced higher pressure and temperature bypass-air entering

11040-399: The same helicopter weight can be supported by a high power engine and small diameter rotor or, for less fuel, a lower power engine and bigger rotor with lower velocity through the rotor. Bypass usually refers to transferring gas power from a gas turbine to a bypass stream of air to reduce fuel consumption and jet noise. Alternatively, there may be a requirement for an afterburning engine where

11160-455: The second running in October 1974. The second engine was then shipped to France and first ran there on 13 December 1974. These first engines were considered "production hardware" as opposed to test examples and were designated as the CFM56-2, the first variant of the CFM56. The engine flew for the first time in February 1977 when it replaced one of the four Pratt & Whitney JT8D engines on

11280-524: The smaller TF34 . More recent large high-bypass turbofans include the Pratt & Whitney PW4000 , the three-shaft Rolls-Royce Trent , the General Electric GE90 / GEnx and the GP7000 , produced jointly by GE and P&W. The Pratt & Whitney JT9D engine was the first high bypass ratio jet engine to power a wide-body airliner. General Electric F101 The General Electric F101

11400-502: The sole requirement for bypass is to provide cooling air. This sets the lower limit for BPR and these engines have been called "leaky" or continuous bleed turbojets (General Electric YJ-101 BPR 0.25) and low BPR turbojets (Pratt & Whitney PW1120). Low BPR (0.2) has also been used to provide surge margin as well as afterburner cooling for the Pratt & Whitney J58 . Propeller engines are most efficient for low speeds, turbojet engines for high speeds, and turbofan engines between

11520-454: The speed of the propelling jet has to be reduced because there is a price to be paid in producing the thrust. The energy required to accelerate the gas inside the engine (increase in kinetic energy) is expended in two ways, by producing a change in momentum ( i.e. a force), and a wake which is an unavoidable consequence of producing thrust by an airbreathing engine (or propeller). The wake velocity, and fuel burned to produce it, can be reduced and

11640-599: The suffix "/2" on their nameplates. GE started developing and testing a new type of combustor called the Twin Annular Premixing Swirler combustor, or "TAPS", during the Tech ;56 program. This design is similar to the double-annular combustor in that it has two combustion zones; this combustor "swirls" the flow, creating an ideal fuel–air mixture. This difference allows the combustor to generate much less NO x than other combustors. Tests on

11760-536: The technology and materials available at the time. The first turbofan engine, which was only run on a test bed, was the German Daimler-Benz DB 670 , designated the 109-007 by the German RLM ( Ministry of Aviation ), with a first run date of 27 May 1943, after the testing of the turbomachinery using an electric motor, which had been undertaken on 1 April 1943. Development of the engine

11880-510: The technology to France would limit the number of American workers on the project. The official decision was made in a National Security Decision Memorandum signed by the National Security Advisor Henry Kissinger on 19 September 1972. While national security concerns were cited as the grounds for rejection, politics played an important role as well. The project, and the export issue associated with it,

12000-497: The thrust equation can be expanded as: F N = m ˙ e v h e − m ˙ o v o + B P R ( m ˙ c ) v f {\displaystyle F_{N}={\dot {m}}_{e}v_{he}-{\dot {m}}_{o}v_{o}+BPR\,({\dot {m}}_{c})v_{f}} where: The cold duct and core duct's nozzle systems are relatively complex due to

12120-673: The trailing edges of some jet engine nozzles that are used for noise reduction . The shaped edges smooth the mixing of hot air from the engine core and cooler air flowing through the engine fan, which reduces noise-creating turbulence. Chevrons were developed by GE under a NASA contract. Some notable examples of such designs are Boeing 787 and Boeing 747-8  – on the Rolls-Royce Trent 1000 and General Electric GEnx engines. Early turbojet engines were not very fuel-efficient because their overall pressure ratio and turbine inlet temperature were severely limited by

12240-428: The turbine inlet temperature is not too high to compensate for the smaller core flow. Future improvements in turbine cooling/material technology can allow higher turbine inlet temperature, which is necessary because of increased cooling air temperature, resulting from an overall pressure ratio increase. The resulting turbofan, with reasonable efficiencies and duct loss for the added components, would probably operate at

12360-425: The turbojet uses the gas from its thermodynamic cycle as its propelling jet, for aircraft speeds below 500 mph there are two penalties to this design which are addressed by the turbofan. Firstly, energy is wasted as the propelling jet is going much faster rearwards than the aircraft is going forwards, leaving a very fast wake. This wake contains kinetic energy that reflects the fuel used to produce it, rather than

12480-445: The turbojet, is lost. In contrast, Roth considers regaining this independence the single most important feature of the turbofan which allows specific thrust to be chosen independently of the gas generator cycle. The working substance of the thermodynamic cycle is the only mass accelerated to produce thrust in a turbojet which is a serious limitation (high fuel consumption) for aircraft speeds below supersonic. For subsonic flight speeds

12600-453: The turbojet. This is done mechanically by adding a ducted fan rather than using viscous forces. A vacuum ejector is used in conjunction with the fan as first envisaged by inventor Frank Whittle . Whittle envisioned flight speeds of 500 mph in his March 1936 UK patent 471,368 "Improvements relating to the propulsion of aircraft", in which he describes the principles behind the turbofan, although not called as such at that time. While

12720-581: The two companies gave GE responsibility for the high-pressure compressor (HPC), the combustor , and the high-pressure turbine (HPT); Snecma was responsible for the fan, the low-pressure compressor (LPC), and the low-pressure turbine (LPT). Snecma was also responsible for the initial airframe integration engineering, mostly involving the nacelle design, and was initially responsible for the gearbox , but shifted that work to GE when it became apparent that it would be more efficient for GE to assemble that component along with their other parts. Development work on

12840-476: The two flows may combine within the ducts, and share a common nozzle, which can be fitted with afterburner. Most of the air flow through a high-bypass turbofan is lower-velocity bypass flow: even when combined with the much-higher-velocity engine exhaust, the average exhaust velocity is considerably lower than in a pure turbojet. Turbojet engine noise is predominately jet noise from the high exhaust velocity. Therefore, turbofan engines are significantly quieter than

12960-418: The two. Turbofans are the most efficient engines in the range of speeds from about 500 to 1,000 km/h (270 to 540 kn; 310 to 620 mph), the speed at which most commercial aircraft operate. In a turbojet (zero-bypass) engine, the high temperature and high pressure exhaust gas is accelerated when it undergoes expansion through a propelling nozzle and produces all the thrust. The compressor absorbs

13080-510: The use of two separate exhaust flows. In high bypass engines, the fan is situated in a short duct near the front of the engine and typically has a convergent cold nozzle, with the tail of the duct forming a low pressure ratio nozzle that under normal conditions will choke creating supersonic flow patterns around the core . The core nozzle is more conventional, but generates less of the thrust, and depending on design choices, such as noise considerations, may conceivably not choke. In low bypass engines

13200-701: The world, with an experience base of over 10 million service hours. The CF700 turbofan engine was also used to train Moon-bound astronauts in Project Apollo as the powerplant for the Lunar Landing Research Vehicle . A high-specific-thrust/low-bypass-ratio turbofan normally has a multi-stage fan behind inlet guide vanes, developing a relatively high pressure ratio and, thus, yielding a high (mixed or cold) exhaust velocity. The core airflow needs to be large enough to ensure there

13320-409: The world. The CFM56 production will wind down as the final 737NG engine was delivered in 2019 and the last A320ceo engine will be delivered in May 2020. Production will continue at low levels for military 737s and spare engines and will conclude around 2024. Unit cost: US$ 10 million (list price) The CFM56 is a high-bypass turbofan engine (most of the air accelerated by the fan bypasses the core of

13440-559: Was abandoned with its problems unsolved, as the war situation worsened for Germany. Later in 1943, the British ground tested the Metrovick F.3 turbofan, which used the Metrovick F.2 turbojet as a gas generator with the exhaust discharging into a close-coupled aft-fan module comprising a contra-rotating LP turbine system driving two co-axial contra-rotating fans. Improved materials, and the introduction of twin compressors, such as in

13560-509: Was considered so important that French President Georges Pompidou appealed directly to U.S. President Richard Nixon in 1971 to approve the deal, and Henry Kissinger brought the issue up with President Pompidou in a 1972 meeting. GE reportedly argued at the highest levels that having half of the market was better than having none of it, which they believed would happen if Snecma pursued the engine on their own without GE's contribution. Nixon administration officials feared that this project could be

13680-660: Was derived from the General Electric J85/CJ610 turbojet 2,850 lbf (12,700 N) to power the larger Rockwell Sabreliner 75/80 model aircraft, as well as the Dassault Falcon 20 , with about a 50% increase in thrust to 4,200 lbf (19,000 N). The CF700 was the first small turbofan to be certified by the Federal Aviation Administration (FAA). There were at one time over 400 CF700 aircraft in operation around

13800-558: Was later selected to re-engine the Boeing 737 . Boeing initially expected this re-engine program (later named the Boeing 737 Classic ) to sell only modestly, but in fact the CFM56's lower noise and lower fuel consumption (compared to older engines for the 737) led to strong sales. In 1987, the IAE V2500 engine for the A320, which had beaten the CFM56 in early sales of the A320, ran into technical trouble, leading many customers to switch to

13920-564: Was made responsible for the day-to-day decision making for the project, while major decisions (developing a new variant, for example) required the go-ahead from GE and Snecma management. The CFMI board of directors is currently split evenly between Snecma and GE (five members each). There are two vice presidents, one from each company, who support the President of CFMI. The president tends to be drawn from Snecma and sits at CFMI's headquarters near GE in Cincinnati, Ohio. The work split between

14040-510: Was officially cancelled in 1977. However the flight test program continued. General Electric was awarded a contract to further develop the F101-102 engine variant. This turbofan eventually powered the B-1B from 1984, entering service in 1986. The B-1's four F101 engines helped the aircraft win 61 world records for speed, time-to-climb, payload and range. The GE F110 turbofan fighter jet engine

14160-608: Was that the Snecma project was the only source of development funds for an engine in this class at this particular time. GE was initially considering only contributing technology from its CF6 engine rather than its much more advanced F101 engine, developed for the B-1 Lancer supersonic bomber. The company was faced with a dilemma when the United States Air Force (USAF) announced its Advanced Medium STOL Transport (AMST) project in 1972 which included funding for

14280-587: Was the Tupolev Tu-124 introduced in 1962. It used the Soloviev D-20 . 164 aircraft were produced between 1960 and 1965 for Aeroflot and other Eastern Bloc airlines, with some operating until the early 1990s. The first General Electric turbofan was the aft-fan CJ805-23 , based on the CJ805-3 turbojet. It was followed by the aft-fan General Electric CF700 engine, with a 2.0 bypass ratio. This

14400-463: Was updated again in the "Evolution" upgrade. The high-pressure turbine stages in the CFM56 are internally cooled by air from the high-pressure compressor. The air passes through internal channels in each blade and ejects at the leading and trailing edges. The CFM56-2 series is the original variant of the CFM56. It is most widely used in military applications where it is known as the F108; specifically in

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