CFM International CFM56
| CFM56 | |
|---|---|
 Rear view of a CFM56-5 | |
| Type | Turbofan |
| National origin | France / United States |
| Manufacturer | CFM International |
| First run | 20 June 1974[1] |
| Major applications | |
| Number built | 32,645 (June 2018)[2] |
| Developed from | General Electric F101 |
| Developed into | CFM International LEAP General Electric Affinity |
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 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 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 was later selected to re-engine the Boeing 737. Boeing initially expected this 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 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.
History
[edit]Origins
[edit]Research into the next generation of commercial jet engines, high-bypass ratio turbofans in 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 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.[3]
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 the Airbus A300.[4] 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.[3]
A major reason for GE's interest in the collaboration, rather than building a 10-ton engine on their own, 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 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 the F101 core technology.[5]
Export issues
[edit]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 the technology to France would limit the number of American workers on the project.[6] The official decision was made in a National Security Decision Memorandum signed by the National Security Advisor Henry Kissinger on 19 September 1972.[7]
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, 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 the beginning of the end of American aerospace leadership.[8]
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,[8] the Dassault Milan. In the end, the Swiss did not purchase either aircraft, opting for the Northrop F-5E Tiger II instead.[9]
1973 Nixon–Pompidou meeting
[edit]
Despite 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 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.[10] 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 the development money provided by the government for the F101 engine core.[3] 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.[11]
CFM International
[edit]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 the 10-ton engine, the CFM56. The venture was officially founded in 1974.[12] 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.[13] 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 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.[4]
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.[4]
The work split between 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).[14] 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.[15]
Development
[edit]Overview
[edit]Development work on 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 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.[16]
The first completed CFM56 engine first ran at GE plant in Evendale on 20 June 1974[17] with 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.[15]
The engine flew for the first time in February 1977 when it replaced one of the four Pratt & Whitney JT8D engines on the McDonnell Douglas YC-15, an entrant in the Air Force's Advanced Medium STOL Transport (AMST) competition.[18] 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,[nb 1] rather than a short bypass duct with unmixed exhaust flow.[nb 2] It was the first to include a "Thrust Management System".[19]
First customers
[edit]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 the CFM56 might be a solution to upcoming noise regulations.[3] 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.[20] Due to limited interest from the airlines in a re-engined 707, Boeing ended the 707-700 program in 1980 without selling any aircraft.[21] Despite the lack of sales, having the commercial 707 available with the CFM56 helped the engine's competitiveness for the KC-135 re-engine contract.[22]
KC-135R
[edit]
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 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.[23]
The USAF announced the CFM56 as the winner of 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.[24] 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, the United States Navy selected the CFM56-2 to power their variant of the Boeing 707, the E-6 Mercury, in 1982.[22] 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.[4]
DC-8
[edit]
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 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;[25] GE and Snecma were two weeks away from freezing development had that order not materialized.[3] 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 the CFM56 a firm footing in both the military and commercial market.[4]
Boeing 737
[edit]
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 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.[26]
Since the small initial launch order for twenty 737-300s split between two airlines,[4] over 5,000 Boeing 737 aircraft had been delivered with CFM56 turbofans by April 2010.[27]
Continued development
[edit]
Tech56 and Tech Insertion
[edit]In 1998, CFMI launched 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.[28][29] When it became clear that Boeing and Airbus were not going to build all-new aircraft to replace 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[30][31] which resulted in better fuel efficiency and lower nitrogen oxides (NOx) 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 the Tech Insertion components. CFMI also offers the components as an upgrade kit for existing engines.[30]
CFM56-7B "Evolution"
[edit]
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.[32] CFMI expected 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%.[33] Following 450 hours of testing, the CFM56-7BE engine was certified by FAA and EASA on 30 July 2010[34] 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.[35]
LEAP
[edit]The LEAP 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.[36]
Electric power generation
[edit]FTAI Aviation in 2026 announced plans to rebuild 100 CFM56 engines annually into 25-megawatt aeroderivative electric power turbines.[37]
Operational history
[edit]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 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.[38]
As of July 2016, 30,000 engines have been built: 9,860 CFM56-5 engines for 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.[39] Lufthansa, launch customer for the CFM56-5C-powered A340, has an engine with more than 100,000 flight hours, having entered commercial service on 16 November 1993, and overhauled four times since.[40] In 2016 CFM delivered 1,665 CFM56 and booked 876 orders, it plans to produce CFM56 spare parts until 2045.[41]
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 the B737NG's -7B and over 100 million cycles and 180 million hours for the A320ceo's -5B since 1996.[42] By June 2018, 32,645 were delivered.[2] Strong demand will extend production to 2020, up from 2019.[43]
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 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.[44]
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 the world.[45]
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.[46]
Design
[edit]Summary
[edit]The CFM56 is a high-bypass turbofan engine (most of the air accelerated by the fan bypasses the core of 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 the booster (low-pressure compressor) evolved over the different iterations of the engine, as did the compressor, combustor and turbine sections.[4]
Combustor
[edit]
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 is separate, and a