Having completed in early May the first of two phases of certification flight-testing of the GE9X engine design that will power the Boeing 777X family, GE Aviation is carefully rebuilding the flight-test engine to incorporate some modified hardware for the second phase, which is due to begin this fall.
As in phase one, GE Aviation (Outside Exhibit P2) will conduct the second phase of GE9X flight testing with the engine mounted on the inner left pylon of the company’s Boeing 747-400 flying testbed, dwarfing the three CF6-80C2 engines also fitted to the aircraft.
GE9X program manager Ted Ingling told AIN, “There isn’t a specific target date” for the start of phase two, “[mainly because] there is a lot of instrumentation to move around” within the engine so that the sensors providing test data to the engineers onboard the aircraft can remain in place after the rebuild is completed. Consequently, a firm start date for the second flight-test phase is “a little difficult to pinpoint…[but] fall is a very good way to think about it. Sooner is better…[but] we can go late into the third quarter or early in the fourth and we can still stay on schedule” to complete certification flight-testing in time for the first sets of GE9X production-standard compliance engines to be able to fly when Boeing is ready to begin 777-9 flight tests. Boeing expects to do so in 2019.
Similarly, GE Aviation has not set a firm target date for completing GE9X certification testing on its flying testbed. “The way we’re thinking about the engine testing and development is all about the [777-9] aircraft and making sure we have completed all the required testing per Boeing,” said Ingling. “We’re thinking less about our certification date” and more about meeting Boeing’s timing requirements: “All our energy is aligned with Boeing and making sure we are ready when they are ready.”
The first phase of GE9X certification flight-testing began on March 13, about two-and-a-half months behind GE Aviation’s original schedule. In December, GE engineers found in that a set of Fadec-activated lever arms was wearing out more quickly than GE had expected—they are located outside the engine casing and used to adjust the positioning of the variable stator vanes in the GE9X’s high-pressure compressor (HPC, so airflow pressure can be optimized during each separate phase of flight.
While GE Aviation performed the first phase of GE9X flight testing with the original lever arms still in place, it decided not to begin flight testing until it had completed investigating the issue and had designed a more robust set of lever arms. Meanwhile, said Ingling, “We did a bunch of required airplane quality checks and regulatory inspections” on the flying testbed so it would be ready as soon as the lever-arm investigation was done.
The first flight-test phase, performed from Victorville Airport in California, involved 18 flights and a total of 105 flight hours, according to Ingling. “One object of the first-phase tests was to get performance [verification] in the critical climb-out and cruise phase, which we did, and we’re very excited about that.” GE also verified the engine’s ability to perform re-starts at high altitudes.
From his experience with past GE large-engine flight-test campaigns, Ingling reckons the second phase will require similar numbers of flights and flight hours as the first phase. In the second phase, GE will validate the engine’s ability to perform air starts and re-starts at mid-range altitudes, and “will be checking out some product enhancements we have made," he said. GE will also verify that the GE9X’s engine-control software is performing to specification. “In the first phase, we got the ball rolling on…the software but we didn’t canvass it.”
Meanwhile, GE9X ground testing is pacing the flight-testing. GE had completed about 25 percent of all required certification ground testing by May but had a variety of required areas still to explore and to validate the engine’s performance. “We classify 25 discrete major campaigns at the engine level and a host at the component level for validation” of the GE9X, Ingling noted.
By early June, GE Aviation had six of eight planned certification-program engines involved in ground-testing, as well as a GE9X core—which consists of the engine’s 11 HPC stages, its combustor and its two high-pressure turbine (HPT) stages—that the company is rebuilding for a new group of tests. (The flight-test engine was the fourth certification engine built, after GE earlier built the prototype first engine to test [FETT] and the second [SETT], plus a ground-test engine.) The last two of the eight ground-test engines were in final assembly by early June and would “join the fleet imminently,” said Ingling.
The first build of the core had already verified the aerodynamic properties of the HPT stages and, by June, GE had also completed verifying what Ingling called the “aero mechanics” of the engine inlet and booster (low-pressure compressor) stages in crosswind conditions, using a ground-test engine. The same engine was then to be dedicated to verifying the operation and aerodynamics of the booster module in clean-inlet conditions. In those tests, “We throttle the engine to move the booster around on its operating line” to check booster operation and aero mechanics at all points on the line, said Ingling. For its new round of tests, the second build of the core “is all about the [high-pressure] compressor aero mechanics,” he added.
Another ground-test engine is to be dedicated to verifying the aero mechanics of the GE9X’s six low-pressure turbine (LPT) stages. “The LPT aero, we still have to do,” said Ingling. “It’s pretty straightforward to do and the outcomes are easy to predict, but we still have to do the tests to get the data. We run a slip ring off the engine to get the rotor data, to transfer the data from the rotating reference to the test facility.”
For certification purposes, other ground-test engines will be used to perform the remaining required ingestion tests. GE completed icing-ingestion testing this past winter and by early June water-ingestion testing was imminent. After that, “we still have to do hailstone and storm, [fan] blade-out and bird ingestion,” said Ingling, as well as vibration and endurance testing, including an endurance “block test.”
However, in designing the GE9X ground-test program, GE did things differently from past commercial-engine development and certification testing campaigns. “We set the program up to place historically difficult tests early on and ran these as engineering [development] tests,” explained Ingling. “The FETT did some of those block tests as engineering tests…to de-risk the program. Now, running the validation of the testbed is a little more straightforward.”
At or near the time it completes GE9X certification testing, GE Aviation will provide Boeing with 10 compliance GE9Xs for Boeing 777-9 certification testing. Boeing will fly four 777-9s in the flight-test program and will have two spare GE9Xs on hand if needed. By early June, GE had begun “vertically stacking the first unit” in final assembly and was “accumulating all the data needed for vertically stacking another two,” according to Ingling.