Advancing Narrow-Body Aircraft Efficiency: Inside the CFM International LEAP Engine’s Design, Development, and Innovations
Introduction
The CFM International LEAP (“Leading Edge Aviation Propulsion”) is a high-bypass turbofan engine designed to power narrow-body aircraft. Produced by CFM International, a joint venture between American GE Aviation and French Safran Aircraft Engines (formerly Snecma), the LEAP engine is the successor of the CFM56 and competes with the Pratt & Whitney PW1000G. The engine’s design and development incorporate several technological advancements, including the use of composite materials, a blisk fan in the compressor, a second-generation Twin Annular Pre-mixing Swirler (TAPS II) combustor, and a bypass ratio around 10–11:1. These innovations are projected to produce 16% lower fuel consumption, providing a more efficient and reliable engine for narrow-body aircraft.
Design
The basic architecture of the LEAP engine includes a scaled-down version of Safran’s low-pressure turbine used on the GEnx engine. The fan features flexible blades manufactured using a resin transfer molding process, designed to untwist as the fan’s rotational speed increases. This design enables the engine to operate at a higher pressure than its predecessor, the CFM56, contributing to its increased efficiency. However, CFM plans to set the operating pressure lower than the maximum to maximize the engine’s service life and reliability.
The high-pressure (HP) compressor of the LEAP engine operates at up to a 22:1 compression ratio, which is roughly double the corresponding value for the CFM56’s HP compressor. This higher compression ratio helps achieve better fuel efficiency and performance. To build the turbine shrouds, CFM uses ceramic matrix composites (CMC), a lightweight and heat-resistant material that further enhances engine efficiency.
The engine also incorporates an eductor-based oil cooling system, similar to that of the GEnx, featuring coolers mounted on the inner lining of the fan duct. According to Aviation Week, “The eductor device produces a venturi effect, which ensures a positive pressure to keep oil in the lower internal sump.” The LEAP engine also boasts some of the first FAA-approved 3D-printed components, showcasing the potential of additive manufacturing in the aerospace industry.
Development
The LEAP engine incorporates technologies that CFM developed as part of the LEAP56 technology acquisition program, which the company launched in 2005. The engine was officially launched as LEAP-X on 13 July 2008, with the intention of succeeding the CFM56–5B and CFM56–7B engines.
In 2009, the Chinese aircraft manufacturer COMAC selected the LEAP engine to power its C919 narrow-body aircraft. The C919 was due to begin testing in 2016. In total, 28 test engines were used by CFM to achieve engine certification, with an additional 32 engines used by Airbus, Boeing, and COMAC for aircraft certification and test programs. The first engine entering the test program reached and sustained 33,000 lbf (150 kN) of thrust, required to satisfy the highest rating for the Airbus A321neo. The same engine ultimately reached 35,000 lbf (160 kN) of thrust in test runs.
CFM carried out the first test flight of a LEAP-1C in Victorville, California, in October 2014, with the engine mounted on the company’s Boeing 747 flying testbed aircraft. The -1C version features a thrust reverser equipped with a one-piece O-ring, replacing the older two-piece door design. The thrust reverser is deployed by the O-ring sliding aft, reducing the drag induced by the older design and improving efficiency. In April 2015, it was reported that the LEAP-1B was experiencing up to a 5% shortfall in its promised reduction in fuel consumption. Despite this challenge, the engine continued to undergo further testing and development.
The LEAP-1B engine went on to obtain its 180-minute Extended-range Twin-engine Operational Performance Standards (ETOPS) approval from the U.S. Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) on June 19, 2017. This approval signifies that the engine met stringent safety and reliability requirements, allowing aircraft powered by the LEAP-1B to operate on routes with a maximum of 180 minutes’ flying time from the nearest suitable airport for emergency landings.
Applications and Customers
The LEAP engine has been adopted by several major aircraft manufacturers and airlines worldwide. The engine is available in three variants: the LEAP-1A, LEAP-1B, and LEAP-1C.
The LEAP-1A powers the Airbus A320neo family, including the A319neo, A320neo, and A321neo aircraft. Major airlines operating the LEAP-1A include American Airlines, Lufthansa, and AirAsia, among others.
The LEAP-1B powers the Boeing 737 MAX family, including the 737 MAX 7, 737 MAX 8, 737 MAX 9, and 737 MAX 10 aircraft. Some of the key customers for the LEAP-1B engine include Southwest Airlines, Ryanair, and Lion Air.
The LEAP-1C is the exclusive engine option for the COMAC C919 aircraft, which is currently under development and undergoing flight testing. The C919 aims to compete with the Airbus A320neo and Boeing 737 MAX families in the narrow-body aircraft market.
Environmental Impact and Future Developments
The LEAP engine represents a significant step forward in terms of fuel efficiency, producing 16% lower fuel consumption compared to its predecessor, the CFM56. This improvement translates to reduced CO2 emissions and lower operating costs for airlines, contributing to the aviation industry’s efforts to minimize its environmental impact.
CFM International is continuously working to enhance the LEAP engine’s performance and efficiency. The company is exploring further advancements in materials, additive manufacturing, and aerodynamics to achieve even greater fuel savings and reduce emissions. These efforts align with the global push for sustainable aviation and the development of next-generation propulsion systems, including hybrid-electric and hydrogen-based engines.
In addition to its focus on technological advancements, CFM is committed to supporting its customers throughout the engine’s lifecycle. This commitment includes comprehensive maintenance, repair, and overhaul (MRO) services to ensure reliable and efficient operations for airlines and aircraft operators worldwide.
Conclusion
The CFM International LEAP engine represents a significant milestone in the development of high-bypass turbofan engines for narrow-body aircraft. With its innovative design, advanced materials, and cutting-edge manufacturing techniques, the LEAP engine delivers improved fuel efficiency, reduced emissions, and enhanced reliability. As the successor to the CFM56, the LEAP engine is poised to power the next generation of narrow-body aircraft, supporting the aviation industry’s ongoing efforts to minimize its environmental impact and meet the demands of a rapidly growing global air travel market.
