DALLAS – The CFM56 high-bypass turbofan aircraft engine made its first flight on a Caravelle flying testbed 45 years ago today in 1977. Despite initial export restrictions, the CFM56 is the most used turbofan aircraft engine in the world and comes in four major variants.
The engine made its first flight in February of that same year, replacing one of the four Pratt & Whitney JT8D engines aboard the McDonnell Douglas YC-15, a competitor in the Air Force’s Advanced Medium STOL Transport (AMST) competition.
On March 17, the second CFM56 was placed on a Sud Aviation Caravelle at the Snecma flight test site in France. This flight, made in Mérignac near Bordeaux, lasted 3 hours and 7 minutes.
The first commercial flight of a CFM56 took place on April 24, 1982, on a Delta Air Lines (DL) DC-8-71 flying from Atlanta to Savannah, Georgia, US. In March 1884, the first flight of the Boeing 737-300 powered by the CFM56-3, which was developed to re-engine the aircraft, took place, followed by its service entry in December.
1984 saw the beginning of the CFM56’s massive market success. That same year, CFMI was already collaborating with Airbus on an engine for the A320, Airbus’ new single-aisle 150-seater.
CFMI is a joint venture between France’s Safran Aircraft Engines (previously known as Snecma) and the United States’ GE Aviation (GE). Both businesses are in charge of component production, and each has its own final assembly line.
The high-pressure compressor, combustor, and high-pressure turbine are manufactured by GE. The fan, gearbox, exhaust, and low-pressure turbine are manufactured by Safran, while some components are manufactured by Avio of Italy and Honeywell of the United States. The engines are built in Evendale, Ohio, by GE, and Villaroche, France, by Safran.
The CFM56 engine is still produced and marketed by the French-American CFM International (CFMI). Despite initial export restrictions, it is the most used turbofan aircraft engine in the world and comes in four major variants.
In the late 1960s, research began on the next generation of commercial jet engines, high-bypass ratio turbofans in the “10-ton” (20,000 lbf; 89 kN) thrust class. Snecma, which had previously mostly built military engines, was the first to seek entry into the market by looking for a commercial partner to design and build an engine in this class.
They evaluated Pratt & Whitney, Rolls-Royce, and GE Aviation as potential collaborators, and a decision was reached after two business executives, GE’s Gerhard Neumann and Snecma’s René Ravaud, met at the 1971 Paris Air Show. The two companies saw the collaboration as mutually beneficial and met numerous more times to iron out the details of the joint project.
As part of their contribution to the 10-ton engine project, GE requested an export license in 1972. The Office of Munitions Control at the US Department of State recommended that the application be denied due to national security concerns.
With the export issue resolved two years later, GE and Snecma signed an agreement to form CFMI, a 50–50 joint venture that would produce and market the CFM56, a 10-ton engine. Ground tests of the first complete CFM56-2 engine started on June 20, 1974, in Evendale, Ohio. However, the joint venture would not receive a single order any time soon. In April 1979, CFMI was on the verge of being dissolved.
The program was rescued when, on March 29, United Airlines (UA) announces an order to re-engine 30 Douglas DC8-71 jetliners with the CFM56-2. This is followed by orders from DL and Flying Tigers (now part of FedEx). The CFM56 was soon chosen to re-engine the US Air Force’s Boeing KC-135 Stratotanker fleet — still its biggest customer.
The CFM56 is a high-bypass turbofan engine that generates 18,500 to 34,000 lbf (80 kN to 150 kN) of thrust (most of the air propelled by the fan bypasses the core of the engine and is vented out of the fan case). There are numerous variations with bypass ratios varying from 5:1 to 6:1.
Although the versions have a similar design, the details change. The CFM56 is a two-shaft (or two-spool) engine, which means it has two rotating shafts, one for high pressure and the other for low pressure. Each one is propelled by a separate turbine component (the high-pressure and low-pressure turbines, respectively).
Several fan blade failure incidents occurred early in the CFM56’s service life, including one that contributed to the Kegworth air disaster, and some engine variants had issues caused by flight through rain and hail. Engine modifications were used to solve both of these problems.
Most notably, the fan and booster (low-pressure compressor), as well as the compressor, combustor, and turbine parts, evolved over the engine’s various versions.
In 2019, the CFM56 fleet passed the landmark of 1 billion flight hours, representing more than 35 billion passengers carried. Before the COVID-19 pandemic, more than 33,400 CFM56 engines were delivered and 28,000 were in service with some 600 operators worldwide.
Featured image: CFM Aero Engines