Engines - Testing of the heavy stuff - Curt Lewis

CFM Lifts Veil On Leap Engine Test Details

Still in the midst of the most intense test effort in its 41-year history, CFM International is poised for simultaneous European and U.S. certification of the Leap-1A, the first of its next-generation engine family destined to power the Airbus A320neo.

Although engine certification is expected on Nov. 20, details of the specific A320neo flight test campaign, along with those planned by Comac for the recently rolled out Leap-1C-powered C919, and by Boeing, remain closely held as a prerogative of the manufacturers. Pitched head-to-head with Pratt & Whitney's PW1100G on the A320neo, Airbus has maintained a close watch on the release of official information for competition-sensitive reasons on the virtually parallel development tracks for the two engines.

However, with certification of the first major model completed, CFM is able for the first time to provide Aviation Week with the most in-depth review yet of the engine-maker's side of the test campaign and to offer some perspective on the behind-the-scenes efforts underway.

Since launching the Leap program, already the largest test effort CFM has undertaken, the General Electric-Snecma joint venture has added more engines to support the "ABC" (Airbus, Boeing, Comac) trio. Part of the reason is the enormous wave of orders for the Leap family, which-with at least seven months still to go before entry into service on the A320neo-stands at just under 10,000 engines. The CFM56, in contrast, passed the same milestone in 1995, some 21 years after the launch of the company and 14 years after entry into service on the DC-8.

"We didn't know that, of course, as we started to prepare," says CFM Executive Vice President Francois Bastin. "What was very clear for us is that it is a reengining program. That means [if] the aircraft will be on time, we have responsibility for the schedule, and we will have to do it. In our mind we were acutely conscious that no one has ever done this before, so our response to that is, 'Let's do it like we've never done it before. Let's not be scared of what we have to do.'" 

Comprising 34 CFM engineering test engines and 48 "ABC" compliance engines, the full test effort is scheduled to include 82 Leap-1A/B and -Cs. "In addition, we have more than 20 engine test stands and two flying testbeds. At no time in history can we find such a commitment over such a short span of time," says CFM President Jean-Paul Ebanga. 

The partners provisioned the test infrastructure to handle the additional workload. "We are not different or better than anyone, but we knew we would do the job and make investments to reach our objectives," says Bastin, who cites the development of a new 12-meter (39-ft.) indoor closed test cell for fan blade-out conditions at Villaroche, France, as an example. "We opened four brand-new test cells to be ready for the expansive test program we had designed: two in Belgium, one in Poland and one in France, on top of the ones we had already prepared for Leap in Villaroche," he says. "We wanted overkill, to make sure we were prepared for risk mitigation at all stages of the program. That's why we ran so many component tests on the [composite] fan. The fan has been a gigantic technology maturation program, so the same spirit was taken to the whole test program as it unfolded. We cannot afford to have a bottleneck or to make compromises-we have to be battle-ready for this."

Worldwide, CFM has run Leap engines at 12 test sites, with a 13th to be added shortly at Avio in Pomigliano, Italy. Aside from the sites in France, Belgium and Poland, the engine has been run extensively at GE sites in Dallas, Peebles and Evendale in Ohio, and West Palm Beach and Eglin AFB in Florida, as well as at the company's icing and endurance test site at Winnipeg, Manitoba. All these sites are being used for engineering and certification engine tests. CFM says in the future maintenance, repair and overhaul (MRO) test cell locations will also be qualified, so that after overhaul an engine can be tested locally. As with the CFM56, these will be sited around the world.

The large number of engineering test engines far exceeds the minimum required for certification, says CFM Leap program manager Gareth Richards: "The GE90 [certification program], for example, was seven engines for the -115B, and the scope is much bigger than we need." Part of the reason for the larger test fleet was the early decision to conduct critical tests well in advance of certification. "We did a practice block test, which is an arduous triple red-line test in which fan and core speed as well as exhaust gas temperature limits are simultaneously exceeded over a sustained period," he says. "We had to build a special engine to do that, and we ran that for about a year before the certification block test. We did the same with icing about a year ahead of the actual certification because they are lengthy tests and time-critical. We wanted to derisk the program by not putting them on the critical path."

Richards says results from any discoveries were then introduced prior to certification tests. "For example, on the icing test we chose to improve the variable stator system and made it more robust, so that was a finding. The other value of that was [that] after we ran the practice icing test, we had a serviceable engine that had sustained stress due to icing," he says. "Now we have an engine that looks like a customer engine, so we brought it back from Winnipeg to Peebles and ran 500 extra cycles on it. And we used it to extend serviceability limits so [that] when the customers receive their first manual there is provision for running it further after it has some distress." The engine has a nick in the leading edge of a compressor blade from ice damage. "We took that credit and put it directly into the service manual, so there will already be an allowance in there that says if you see this condition it is acceptable," he adds.

Another batch of 48 engines is being delivered to the three airframe makers to show compliance to the specification for flight testing. As of early November, 12 engines had been delivered, with the majority going to Airbus, which will shortly have three Leap-1A-powered A320neos in flight test. At least one shipset of Leap-1Bs has been delivered to Boeing for the first 737 MAX, due to roll out in December, while another set has been sent to China for the initial C919, which was unveiled in November.

The first Leap-1A-powered A320neo flew on May 19 and was joined by a second test aircraft on Sept. 29. According to program sources, the two aircraft had accumulated more than 360 flight hours and almost 145 flights by mid-November. Both the 737 MAX and C919 are expected to enter flight test in 2016. 

"Tests are going flawlessly," says Richards. "There are no engine issues or concerns identified in flight test to date."