CFM in talks on new narrowbody turbofans

Singapore Air Show » 2010
February 2, 2010, 1:42 AM

CFM International continues to work “on a daily basis” with Boeing and Airbus on new engine applications for the 737 and A320 families, according to Eric Bachelet, president and CEO of the General Electric-Snecma joint venture. Offering its new Leap-X series as the basis for any contribution it would make to either of the airframer’s re-engining efforts, CFM has already won a place on the Comac C919, the engine for which Bachelet said would start running by the end of 2012 or early 2013. Any time-frame projection for a Boeing or Airbus application would have to come from the OEMs themselves, however.

“I will not answer for them on that,” said Bachelet, who did, however, acknowledge that the prospects of re-engining the respective single-aisle airframes have gained momentum recently. “In the last year we felt that the case for the re-engining was growing stronger, and we have had continued discussions with them around our Leap proposal. As you know very well, they have not made a decision yet, although the case seems to be pressed harder and harder, I would say, especially with Airbus, which made a public declaration.”

Reports that CFM has signed an MOU with Airbus have proved premature, however. “We do not have a signed agreement with Airbus,” a CFM spokesperson told AIN a little more than a week before the start of the Singapore show.

CFM finished the first phase of testing late last year in what Bachelet characterized as “a relatively long run” of the Leap-X program’s first core. That testing measured performance parameters related to the combustor and high-pressure turbine. The second phase, scheduled to begin some time next month, will center on the engine’s compressor.

CFM has also run a 71-inch, full-scale demonstrator of the engine’s fan on the front of a CFM56-5C core. Consisting of blades made of 3-D woven composites, the fan will weigh some 1,000 pounds less than a similarly sized fan made with metallic blades. The weight savings have allowed CFM to increase the size of the fan, thereby allowing it to turn slower and double the bypass ratio now produced in a CFM56 to 10:1 on the Leap-X. As we approached the start of the show, CFM was preparing to begin running a 5,000-cycle endurance test on the fan.

Bachelet reported that the composite blades “have performed absolutely, remarkably well.” The chief executive explained that perhaps the most imposing challenge related to the composite technology has centered on “downscaling” the blades from the size used in the massive GE90. At 71 inches, the blades used in the Leap-X demonstrator must absorb the same bird-strike forces over a smaller area.

“You have the area, the thickness of the blades and so on, so it’s all easier [with larger blades]” said Bachelet. To achieve the same bird-strike resistance, CFM opted for a solid 3-D woven preform in place of the laminated design used for the GE90’s blades.

Although CFM targets an eventual 16-percent fuel burn improvement over current generation CFM56, the company won’t achieve that level of benefit for the C919 because the Leap-X, in essence, involves a series of incremental improvements as time advances. Rather, for Comac, it expects to offer somewhere between 10 and 15 percent.

By 2014, the engines for the C919 won’t, for example, employ ceramic matrix composites in the low-pressure turbine blades and certain high-pressure turbine components CFM plans for later iterations. That technology will have to wait until CFM can guarantee that the material can withstand the kind of high-cycle, fast-turn environment common to CFM56-powered airplanes. “We have internal processes that do not allow us to make a solid commitment on an engine if the technology hasn’t been demonstrated and the capacity to mature it has not been thoroughly evaluated,” said Bachelet. “At this stage, for the ceramic matrix composite, we are not there yet.”

Bachelet estimated that the company would need roughly three years to develop the technology to its satisfaction. When it does, the ceramic matrix material will help lower the weight of the low-pressure turbine by taking advantage of its lower density versus super alloys. In the high-pressure turbine, CFM expects the ceramic components to aid temperature capacity, thereby attenuating cooling requirements and adding to cycle efficiency.

Of the 16-percent fuel burn improvement CFM expects to achieve, some 7 percent would come from the performance of the core, said Bachelet. Another 7 percent would come from an improvement in propulsive efficiency by virtue of the much higher bypass ratio in the Leap-X. The final 2 percent would come from what Bachelet described as other systems contributions.    

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