GE Aviation’s Boeing 747-400 flying testbed in Victorville, California, is ready to receive the first GE9X test engine.
Boeing engineers have modified the aircraft with a strengthened wing and a new pylon – both needed to accommodate the 339cm (133.5in)-diameter inlet fan of the 105,000lb-thrust GE9X, the largest turbofan engine in aviation history. The fourth assembled GE9X engine is off the test stand at GE’s ground-test centre in Peebles, Ohio, and is being prepared for a cross-country journey to California to begin flight tests.
Thus, the stage is set. By the end of the year, GE expects to complete a familiar ritual. Over the past decade, the series of CFM International Leap-1 family engines and the GE Passport engine have transferred to the flight test team in Victorville just as most of their corporate co-workers enjoyed their Christmas and New Year holidays. The GE9X is on schedule, and is coming next.
“It’s like it’s a Christmas present to the guys down in California,” jokes Ted Ingling, general manager for the GE9X.
Boeing has started building the first structural parts of the 777-9, the first member of the 777X family that the new GE9X is selected to power. The 777-9 is scheduled to begin airworthiness testing in 2019, which is shortly after GE plans to receive US Federal Aviation Administration certification for the GE9X. Boeing is replacing the 777’s metallic wing with a more efficient, composite structure, but about half of the 777X’s promised fuel efficiency improvement is down to the GE9X.
So the upcoming flight tests on GE’s 747-400 will provide the strongest data yet on how well the GE9X meets those promises.
“We’ve certainly got a big test coming up with the flying testbed,” Ingling says. “We’ve done all of our testing to date on the ground. We’re very comfortable with the engine as it shows to us on the ground. We project what it looks like up at altitude and we will know pretty soon what it looks like at altitude.”
GE has some reason for confidence in the company’s projections of the GE9X’s flying performance. Although it shares no common part numbers or operating conditions, the architecture of the GE9X is derived from the GE90-115B, which grew out of the original GE90 series introduced in the mid-1990s.
The upcoming flight tests will serve as a sort of graduation exercise for the new features and technologies that GE packed into the GE9X in order to best the fuel efficiency of the 15-year-old GE90-115B by 10%.
The most distinguishing feature of the GE9X is, of course, the 339cm fan, which is 9cm wider than the same module on the GE90-115B. It is so large that GE needed to modify its test stand and wind tunnel in Winnipeg, Canada. When GE’s engineers designed the test stand, they built it to support an engine with greater thrust than the 115,000lb-thrust GE90-115B, but not greater size.
“We think of the stand as being sized by thrust so we set them up to be able to handle the thrust,” Ingling says. “But nobody was thinking of the fan diameter, per se, as another constraint.”
The purpose of enlarging the fan of the GE9X by 9cm compared with the GE90-115B is to increase the ratio of air bypassing the core of the engine to the airflow that enters the core, but it is only part of the solution. In addition to increasing the fan diameter, GE also designed the engine with 16 fan blades, six fewer than found on the GE90. With fewer fan blades, the GE9X’s designers were able to narrow the diameter of the fan hub, which further increased the airflow capacity to run through and around the engine core.
As well as increasing the airflow, GE also designed the GE9X to manage the combustion process more efficiently. Air entering the compressor is compressed to an unprecedented 27:1 ratio by the time it reaches the combustor, where it is mixed with fuel and ignited to produce energy and thrust. As the mixture exits the combustor, special care must be taken with the design and the materials of the turbine module to endure temperatures never seen before in a commercial turbofan. So GE replaced metal components with ceramic matrix composites in the combustor liner and turbine shrouds. The hollow turbine blades are designed with small air passages, with streams of cooler air siphoned from the compressor module preventing the metal parts from melting.
To reduce the risk of new technologies delaying the GE9X certification schedule, GE transformed its internal development process. So the first engine to test (FETT) arrived in Peebles in April 2016, or about 13 months ahead of the second engine to test (SETT), rather than just days or weeks apart. In effect, that made the FETT a demonstrator engine rather than a certification test article.
“That first engine was a good vehicle to tell us about the engine architecture and all the components,” Ingling says. “We learned some things that we needed to correct and we had 13 months to do it and we fixed it all.”
Since the SETT was delivered to the test stand in Peebles in May, the engine has run about 200h in ground testing, Ingling says. As GE begins flight testing with the fourth engine, the SETT will run through a battery of the most difficult ground tests, including a second round of pre-certification icing trials and the critical round of endurance trials, he says. Meanwhile, the third engine now in Peebles will be used for crosswind testing. GE has also delivered the seventh engine to the Peebles test centre, where it will be used for certification icing tests next year.
Ingling says: “Right now, we’re very happy with the engine’s performance and we’re looking forward to putting that engine on our 747-400 by the end of this year.”