Farnborough Air Show

Leap-X tests hitting their mark

 - July 15, 2010, 4:12 AM

CFM International has completed the second phase of testing of the Leap-X core demonstrator known as eCore 1. This means that all three major elements of the first core–the turbine, the combustor and the compressor– have undergone evaluation. The results, according to Leap program director Ron Klapproth, have matched or exceeded all the company’s early projections, leaving the program on schedule for certification in late 2014.

“We’re very pleased with the results,” said Klapproth, who explained that the company first tests each of the components separately to evaluate different design concepts and choose the configuration to use in the core. “When we get to the point of running the core we have a pretty good idea of how we think [it] should perform. The fact that we’re getting back results that are very much in line with what we expected says that whole process is working well.”

In some cases, said Klapproth, the results have proved better than originally expected. Overall, he added, “we’re right where we expected to be.” By the end of the second phase of testing, the core accumulated more than 150 test hours. On some days it ran for as long as 10 hours.    

Nonetheless, the test program remains in its early stages, as CFM prepares to build the second of three core demonstrators. Engineers have removed the first test vehicle from its test cell and have taken it apart to inspect the condition of the hardware. Hardware for the second core–eCore 2–has begun to arrive, as the company prepares for the instrumentation cycle. “These cores have tremendous amount of instrumentation on them,” said Klapproth. “A lot of times it turns out that instrumentation cycle is the longest part of the build cycle.”

The second core demonstrator will include a full 10-stage compressor and two-stage high-pressure turbine, while eCore 1 contained an eight-stage compressor and a single-stage high-pressure turbine. “ECore 1 is the CFM-type architecture; eCore 2 is the Leap-X architecture,” said Klapproth, “so we take all the learnings from eCore 1 and design the hardware for eCore 2.”

CFM expects the third demonstrator to start running roughly a year after the start of eCore 2’s testing. Looking much like eCore 2, with its 10-stage compressor and two-stage HP turbine, eCore 3 will undergo what Klapproth described as minor tweaks or tune-ups. “We’ll find some areas in eCore 2 that we can improve upon,” he said. “We’ll make those changes and test them, and then we’ll head into the product certification cycle.”  

Test Results Promising
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.

 “We’ve run additional component level rig testing on bird strikes and actually did a blade-out test,” said Klapproth. “The results are actually looking better than our calculations had first predicted. Our more recent calculations are coming in more in line with the test results. I would say today that the test results matched the analytical predictions very well, which is remarkable.”

Perhaps the most imposing challenge associated with the composite technology used in the fan has centered on the “downscaling” of the blades 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, hence the reason CFM elected to pursue the solid 3-D woven design.

Chinese Application
Chosen by China’s Comac to power the new C919 narrowbody airliner, the Leap-X1C would start running by early 2013. Plans call for the certification program to use eight engines running a total of 18,000 cycles. Klapproth attributed the decision to run the relatively high number of cycles (a typical engine runs 15,000 cycles) to the expected operating profile of the Leap-X. “Leap-X being a high-cycle motor, we want to run more cycles in the factory than we typically would,” he said.    

Comac, of course, would like to see its C919 perform as reliably as a 737 or A320 in a high-frequency operating environment, requiring an engine that will absorb just as much punishment as the CFM56 while delivering double-digit fuel burn improvements. Airbus and Boeing, too, in their search for a narrowbody engine replacement will place a premium on reliability as well as fuel economy.

Although CFM targets an eventual 16-percent fuel burn advantage over the CFM56 for an all-new airplane, it won’t achieve that level of improvement with a re-engining of an existing airframe, said Klapproth, who rather promised a double-digit benefit. In fact, the company targets between 10 and 15 percent for even the C919 because the Leap-X, in essence, involves a series
of incremental improvements as time advances.  

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.

The company estimates it will need some 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 superalloys. 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 eventually expects to achieve, about 7 percent would come from the performance of the core, another 7 percent would come by virtue of its higher bypass ratio and the final 2 percent would come from what Klapproth called integrated systems. “That encompasses a lot of things,” he said. “The biggest one is what we call integrated propulsion system, which is where we truly integrate the design of the engine and the nacelle from day one.”