Reader Response Draft #2

The CFM56 is a family of high-bypass turbofan aircraft engines produced by CFM International, a 50/50 joint company between Safran Aircraft Engines and GE Aerospace (CFM International, 2024). The CFM company has produced several series in its engine family to cater to the needs of such aircraft including the military. Each series is a better, more updated version of its predecessor. According to the 2024 CFM Technical Manual Index, the CFM56 engine series includes the CFM56-2A, 2B, and 2C series, the CFM56-3 series, the CFM56-5A, 5B, and 5C series, and the latest, the CFM56-7B series, which exclusively powers Boeing 737 Next Generation (737NG) single-aisle aircraft. The CFM56-7B can generate between 23,000 and 32,900 pounds of thrust (CFM International, 2024). According to an article by CFM in 2018, the CFM56-7B engine, which debuted on the Boeing 737 in 1997, has been a reliable workhorse in the airline industry. Collectively, this engine fleet has logged over 350 million flight hours. 

I feel that given the long accumulated flight hours, the CFM56-7B has proven itself to be a cornerstone of the aviation industry. Even though it is not the most advanced engine that is available today, it has built an excellent reputation based on its efficiency, reliability and longevity.

The CFM56-7B features a standard two-shaft design with a 61-inch diameter fan. Behind the fan, there is a three-stage low-pressure compressor (LPC), a nine-stage high-pressure compressor (HPC), a single-stage high-pressure turbine (HPT), and a four-stage low-pressure turbine (LPT) that drive the fan and LPC (Aircraft Commerce, July 2008). A short video listed on the CFM website describes how the CFM56-7B works. In an article by Aircraft Commerce in 2010, the engine supports 180-minute extended-range twin-engine operations (ETOPs) and features full authority digital electronic control (FADEC). While it is based on the CFM56-3, the -7B includes many advancements from the CFM56-5A/B series, along with its own unique improvements. The bypass ratios for the -7B series range from 5.1 in the highest thrust variant to 5.5 in the lower thrust variant. In contrast, the -3 series has a bypass ratio between 4.9 and 5.0:1. A higher bypass ratio would mean that a higher bypass ratio increases fuel efficiency by generating more thrust from cooler airflow bypassing the engine core, reducing fuel consumption. This also makes the engine quieter by minimizing high-speed exhaust noise and helps lower carbon emissions, aligning with environmental standards.

According to an article by CFM (2020, October 29), the United States Air Force (USAF) contracted the CFM56 engines to be used in their KC-135 aircraft re-engining program. They have publicly cited that the CFM56 engines had a “higher performance, lower life-cycle costs, lower noise, and easier support as the reasons for its selection”. This program had proven to be highly successful and the USAF remained as CFM’s biggest customer. However, the USAF has determined that the current engines will not be viable beyond 2030 thus, they plan to upgrade older planes to use the CFM56-7B engine which offers higher thrust, better fuel efficiency, and meets environmental standards. Furthermore, Upgrading older aircraft with these engines would enhance performance and extend their service life, supporting the USAF’s Advanced Battle Management System (ABMS) development (CFM 2020). The CFM56-7B gearbox can also manage high electrical power demands, and the engine can be installed without a thrust reverser to reduce weight. These engines, utilized in military Boeing 737 applications, remain in production and are supported by robust networks. These applications in the military prove the reliability and versatility of the CFM56-7B (CFM, 2020).



[References]


CFM International (2024). CFM56 - CFM International Jet Engines CFM International https://www.cfmaeroengines.com/engines/cfm56/ 


Chelsey Levingston (2019, June 4). 1 Billion Flight Hours: “World-class experience” builds 15,000th CFM56-7B engine https://www.geaerospace.com/news/articles/manufacturing-paris-airshow-people-product/1-billion-flight-hours-world-class-experience 


One Monroe Aerospace. (2023, December 1). Low vs High Bypass Turbofan Engines: What’s the Difference? https://monroeaerospace.com/blog/low-vs-high-bypass-turbofan-engines-whats-the-difference/ 


CFM (2024, October 1) Technical Manual Index https://www.cfmaeroengines.com/wp-content/uploads/2024/10/CFM56-Engine-Manuals-Index.pdf


Aircraft Commerce (2008, July, Issue No. 58) CFM56-7B series specifications

https://www.aircraft-commerce.com/wp-content/uploads/aircraft-commerce-docs/Aircraft%20guides/CFM56-7B/ISSUE58_CFM56_7B_SPECS.pdf


Aircraft Commerce (2010, July, Issue No. 70) 737NG family & CFM56-7B specifications, fleet & developments

https://www.aircraft-commerce.com/wp-content/uploads/aircraft-commerce-docs/Aircraft%20guides/737NG-600-700-800-900/ISSUE70_737NG_SPECS.pdf 


CFM (2018, April 20) CFM International issues new service bulletin to CFM56-7B operators 

https://www.cfmaeroengines.com/press-articles/cfm-international-issues-new-service-bulletin-cfm56-7b-operators/ 


CFM (2020, October 29) CFM56-7B Offers Reliability, Life Extension for Boeing 707 Platforms

https://www.cfmaeroengines.com/press-articles/cfm56-7b-offers-reliability-life-extension-for-boeing-707-platforms/ 

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