Smooth Start To Fast-Paced Leap-1A Test Program

By Guy Norris
Source: Aviation Week & Space Technology

From a schedule perspective, the monumental effort got off to a good start when the first engine entered testing three days earlier than the target date established when the program was laid out in 2010. “We also got combustor light-off first time, and the first day we did mechanical check out,” says Ingling. Full power was achieved five days later with a run up to 33,100 lb. thrust to cover the highest rating required for the A321. The first engine was then pushed further, demonstrating more than 35,000 lb. thrust and with it the availability of fundamental growth margin, should it be required, adds Ingling.

“In early testing, we're looking at the initial performance of the engine, vibration and the aero-mechanics,” he says. “We do runs to check the fan and compressor blades, the engine dynamics and the bearings. There's also a lot of starting to map out the start envelope, figure out the fuel schedules and see how the starter interacts with the engine.”

The Leap's basic architecture is based on a scaled version of the same eCore design at the heart of the GEnx, with an advanced low-pressure (LP) system from Snecma. However, while the Leap core is designed to operate at a higher pressure ratio than the latest CFM56, it is deliberately tuned to lower pressures than the bigger GE engine that powers Boeing's 787 and 747-8. “We're well inside GE's experience for these kind of pressure ratios,” says Ingling. “The GEnx is the high watermark in terms of pressure ratio and temperature and, although we had the option to mimic or even exceed the GEnx, we didn't because we wanted durability for this marketplace. We want it to be a copy of the CFM56 in terms of time on wing.”

The third version of the eCore ran earlier this year in the build-up to Leap testing. “Using this, we have done aerodynamic, stall, performance-mapping and so on, but what we don't get effectively is interaction with the LP system and we don't get transients [rapid changes between thrust demand],” says Leap program manager Gareth Richards. The full-up engine is also therefore the first to check the full operability characteristics of the integrated LP and high-pressure (HP) systems. Testing includes “bodies”—or throttle bursts and chops—that check the related response of the compressor.

The engine is also fully configured with standard systems such as the eductor-based surface oil-cooling mechanism that, like the same system on the GEnx, consists of surface coolers mounted around the inner lining of the fan duct. The eductor device produces a venturi effect, which ensures a positive pressure to keep oil in the lower internal sump.

Engineers are also verifying the performance and behavior of the composite fan using “clearance-ometers” developed by Snecma to sense the exact motion and vibration of individual blades. The sensors are mounted in the fan case at the leading-edge, mid-chord and trailing-edge positions to measure variations in the local magnetic field as each blade passes by. Using careful “per-rev” calculations, engineers can deduce from the measurements whether the blades—and specific parts of each blade—are passing the sensors early, late or on time. The results indicate whether the flexible blade, made by Snecma using a resin transfer molding (RTM) process, is untwisting to the correct degree with increasing rotational speed.

“The untwist we're looking for is right on the prediction,” says Richards. “That calibrates the engine models, which say as the engine speed goes up, forces act on the fan, and we use those sensors to be witness to the fan mechanical characteristics. All of this is confirmation of our analysis. We are validating what we expect the engine to be doing.”

In the case of the fan, CFM also continues to run parallel validation tests of the final blade configuration in a demonstrator, even as the first Leap engine starts to run. The final phase of the Mascot 2 program, which involves testing an RTM fan on a CM56-5C, is now underway with a series of crosswind evaluations at Peebles. “This is building confidence ahead of further runs,” adds Ingling.

The first engine, designated 598-001, is festooned with 1,300 pieces of instrumentation. These include thermocouples in rotor cavities “to understand the secondary systems, feed and purge cavities, loads and temperatures of the bearings,” says Richards. “We also have performance rakes to understand how the fan is pumping and how the core is pumping,” he adds. Following its first phase of testing, the first engine will go through a second build cycle in readiness for early icing tests at GE's dedicated facility in Winnipeg, Manitoba.

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