Farnborough Air Show

CFM Striding Forward With Leap Developments To Power New Narrowbodies

 - July 8, 2012, 2:50 AM

CFM International remains on track with development process of the Leap series of engines that it laid out four years ago. The 50/50 partnership between General Electric and Safran subsidiary Snecma announced it has recently frozen the designs for its new Leap 1A and 1C engines destined for use on the Airbus A320neo and the Chinese Comac C919 narrowbody airliners, which are scheduled to enter service in 2016.

The 40-year-old U.S.-French joint venture saw a tremendous industry appetite for the developing powerplant at last year’s Paris Air Show. According to a CFM spokeswoman, prior to the event, the company had 200 orders on the books, but, by the time the dust settled in Paris four days later, that total had skyrocketed to more than 1,100.

The company currently has 3,626 orders and commitments for the 20,000- to 34,000-pound-thrust Leap series engines, which have been selected to power more than 1,800 aircraft, including 578 A320neos (Leap 1A), 235 Comac C919s (Leap 1C) and 1,000 Boeing 737 MAXs (Leap 1B). Those engines are worth a potential $43.5 billion, a number that is expected to grow here at this week’s Farnborough International Airshow.

For the A320neo, the company shares the powerplant market with Pratt & Whitney’s PW1000G, and it currently claims a 54.2-percent share of engines for that aircraft. “We don’t necessarily target a market share above 50 percent,” said Cedric Goubet, CFM International’s executive vice president. “Our target is a balanced market share of 50-50.”

The engine design for the Leap 1B lags the others by nine months, reflecting Boeing’s pause in announcing the launch of the 737 MAX. CFM, which is the sole source supplier on the Boeing and Comac aircraft, has told the Seattle airframer that it is ready and willing to accelerate the pace of its engine development should Boeing require it earlier.

The new engine will eventually succeed the company’s popular CFM56 series, which at more than 22,000 copies has seen three decades of service. CFM promises to imbue Leap with the same reliability and maintenance costs of the earlier engine, as well as make notable improvements in several areas such as fuel efficiency (15 percent improvement), nitrous oxide emissions (50 percent lower than current CAEP 6 requirements) and noise (compliant with new Chapter 5 regulations).

GE and Snecma split the component design for the new powerplant, with GE’s engineers handling the core and Snecma tackling the fan, fan case and low-pressure turbine duties. CFM has released the engine’s cross section for the first time and it shows off some of the features, which contribute to its efficiency gains over the previous model.

The new fan has 18 blades compared to up to 36 for the -56 series. Those blades as well as the fan case are constructed of carbon fiber, woven in three dimensions, and resin cured in a new proprietary process that results in an extremely durable part. The blades are larger, yet lighter than their metal counterparts, requiring little to no maintenance or cycle limitations and are expected to last the life of the engine.

The use of the new composites for the fan was one of the ways Snecma was able to increase its size (especially on the 1A and 1C, which have a diameter of 78 inches as compared to 69 for the 1B). The use of a larger heavier metal blade would have necessitated a thicker fan casing to protect against blade out situations. With the new composite fan and case, CFM was able to nearly double the bypass ratio from the -56’s, while simultaneously reducing the on-aircraft weight of the engines by nearly 1,000 pounds.

Carbon Matrix Composites

Another new material technology developed by GE’s Global Research Center in upstate New York will make its debut on the Leap engine. Carbon matrix composites (CMC) will be used to make the stage-one turbine shrouds. Consisting of fibers of silicon carbide measuring one fifth the diameter of a human hair and embedded in a silicon matrix, a part made of CMC has one third the weight of a comparable structure made out of nickel alloy and can operate in higher temperatures thus reducing the need to route cooling air from the compressor. This leaves more for thrust generation and adds to the overall increase in engine efficiency.

Since the early 1990s GE has accumulated nearly one million hours of testing on the materials, including their use on industrial gas turbines manufactured by the company. Though the company has taken the first steps to introduce this material to the engine, according to Sanjay Correa, vice president of the CMC program at GE Aviation, if all the appropriate parts in the hot-gas path were replaced with CMC, it would result up to a 1.5-point decrease in fuel burn, which over the span of 10 years would equate to approximately $700,000 in savings for a typical twin-engine narrowbody passenger aircraft at today’s fuel prices.

While currently limited to static parts, Correa said the use of CMC for rotating parts is on the roadmap but not until the technology is fully validated. “CFM has fantastic reliability,” said Correa during a pre-show tour of the facility. “We’re not going to put anything into an engine that doesn’t preserve that level of reliability.”

Additive Manufacturing

Another family of technologies known as additive manufacturing will also be used to create parts for the new engine. While the manufacturer declined to identify exactly which parts will be constructed using the processes, which build them a layer at a time, the resulting parts are lighter than their traditionally cast counterparts, with strength added only where operating stresses require it. Eventually the method of production will earn additional production savings by reducing the “buy-to-fly” or raw materials wasted to produce parts.

Also factoring heavily in the engine design is research, which will enable it to withstand flow-path temperatures with less cooling while simultaneously maintaining durability. Using computational fluid design and real-world testing, GE’s engineers investigated the optimum patterns for developing protective “cooling films” on critical hot-section components.

Despite its name, the new engine was not a leap of faith in terms of architecture, borrowing tried and proven designs from current engines such as the GE90 and the GEnx. According to the company, the powerplants share so much in terms of design that any future upgrades to one of them will easily translate to the others.

The engine’s combustor is the lean burning twin-annular premixing swirler (TAPS) II design found in the larger GEnx, which results in lower emissions as well as reduced maintenance costs to the combustor and high-pressure turbine as a result of more uniform temperatures. The efficient debris rejection system modeled after the GE90’s inward opening variable-bleed valve doors promise the new engine better fuel burn retention than engines with non-inward opening doors by reducing the amount of debris that reaches critical engine components.

By including a smaller version of the 10-stage compressor found in the GE90 and GEnx, the manufacturer managed to double the pressure ratio from the earlier -56. As a result of all the improvements in cooling, materials and efficiency, the engine will run hotter than the CFM56 to achieve improved fuel burn, but CFM says, initially, it will not run as hot as its larger engines in order to preserve its time-on-wing in a high-cycle environment.

“Once we get out into service and we see how the engine is operating, if it’s operating as we expect it to, we can get a pretty quick performance improvement just by running the operating line up and running the temperatures up to levels that we run today on the widebody engines,” said Ron Klapproth, product strategy manager for GE Aviation.

According to CFM, it successfully tested the eCore demo 2 on at the end of May, one month ahead of schedule, and will have eCore 3 scheduled to run early in 2013. The first full engine test is slated for the third quarter of next year, followed by the commencement of flight testing on the company’s testbed in 2014.