GE Aviation has spent six years designing, testing and tweaking the engine now officially dubbed the GE9X-105B1 for Boeing’s 777X family.
Two years were spent maturing the technology at the component level while fighting off a competing bid from the Rolls-Royce RB3025 to re-engine the widebody twinjet. Another four years have been spent steadily making progress since Boeing’s selection in 2013 of GE’s turbofan with a then-3.37m (132.5in) diameter fan; tests have moved from components up to modules, and from modules up to full rigs of the core and low-pressure section. Finally, the first full engine – with a fan diameter slightly enlarged to 3.4m – was sent into developmental testing last year.
With the second GE9X engine now commissioned at GE’s Peebles Test Operation (PTO) in Ohio, GE finally begins to find out how much that investment in six years of preparation was worth. Unlike the first engine to test (FETT), which was devoted to discovering any flaws in the original design, the second engine to test (SETT) represents the version that GE believes is ready to qualify for airworthiness certification at the engine level.
Boeing expects to start flying a future GE9X-105B1 on the first 777-9 next year, but GE plans to continue a battery of ground and flight tests on a company-owned 747-100 flying testbed through early 2019, says Ted Ingling, GE9X general manager at GE Aviation. A total of eight engines will be used in GE’s engine-level certification activity, including the FETT and the SETT powerplants already commissioned. The one-year gap between the delivery of the FETT and SETT was unusually long, but gave GE a chance to begin certification testing with an engine that closely matches a future production standard.
“This approach of separating FETT from SETT by more than 12 months is a first for us. It was purposefully implemented to move through cert more confidently and with a stable configuration,” Ingling explains. “Following those FETT tests, we are very happy with the way the engine is set after analysing the interaction of all the components. As you know, when we develop a product, we start with small parts and move to subassemblies and then to modules. The FETT engine is the first time we brought all of our analytical understanding of the engine to reality. The engine performed exactly as we expected.”
Of course, one of GE’s expectations for the FETT was to identify any flaws that must be corrected before the beginning of certification testing, when any tweaks would require costly rounds of re-testing. In a year-long series of tests with 162 cycles in 168h to cover more than 50 test points, GE found about five or six “minor” problems with the FETT configuration – the cooling system for lube units, for example.
“We found the amount of heat we were picking up and the amount of heat we were discharging was more than capable to this system, so were able to simplify the engine relative to the amount of coolers we had. That’s a great development – it’s a byproduct of the time, money and execution we’ve put into this programme upfront, to achieve a stable configuration heading into certification testing,” Ingling says.
“We also took our first look at operational clearances across the engine and as a result have modified our build procedures to tune the engine to meet design intent,” Ingling adds.
The FETT testing spanned nearly 12 months, creating data on aerodynamic and aero thermal testing, as well as mechanical verification. After a first round of testing that concluded last summer, GE launched a second round of testing in December devoted to examining how the engine handles in icing conditions.
“Icing tests are hard to predict. We have found that testing the system with a real engine can yield valuable learnings and thus reduce risk,” Ingling says. “The FETT performed outstandingly during these icing tests. We went through more than 50 test points to evaluate the conditions that are created by the agencies to clear cold and operational icing conditions.”
The testing on the GE9X is covering new ground. GE designed the engine to reduce fuel burn by 10% compared with the GE90, the engine that powers the original series of 777 widebodies that debuted in 1995. To achieve this improvement, GE largely retained the architecture of the GE90, but refreshed the design with a suite of new technologies far beyond the state-of-the-art available to GE90 designers 25 years ago.
The 129.5in-fan diameter of the GE90 left little room for improving the bypass ratio, the measure of air passing around the core that generates the majority of, and most efficient, thrust. Instead, GE focused on improving the pressure ratio by focusing on the GE9X core: the high-pressure compressor, combustor and high-pressure turbine. Whereas the GE90 series was configured for either nine or 10 stages of compression, a compressor pressure ratio of 19 and an overall pressure ratio of 40, the GE9X high-pressure compressor features 11 states, a compressor ratio of 27 and an overall pressure ratio of about 60. The GE90 debuted in 1995 with the last iteration of dual annular combustor technology, but GEnx is designed with a third-generation, twin-annular pre-swirl (TAPS) combustor.
New materials will also play a major role in GE’s certification drive for the GE9X. Like many technologies in GE9X, GE started applying new materials in preceding engines. Ceramic matrix composites, for example, are used in the hottest part of the CFM International Leap engine, which is produced by a joint venture of GE and Safran (formerly Snecma). CMCs are a blend of ceramic fibres in a ceramic matrix. The combination produces a material lighter than metal that can endure hotter temperatures.
Although not introduced first on the GE9X, the 777X powerplant dramatically expands the application of CMCs in turbine engines beyond the stage 2 turbine shroud in the Leap engine. The GE9X features CMCs in two combustor liners, two nozzles and the shroud. In 2013, GE considered applying CMCs to the first-stage turbine blades, where they are subjected to extremely high thermal and centrifugal forces, but decided to wait for another iteration of the technology.
In addition to the FETT engine, GE has subjected the CMCs to a battery of endurance testing in another representative engine. A company-owned GEnx engine, which powers the Boeing 747-8 and 787, was fitted with the CMC parts destined for the GE9X over two extended series of tests totalling 4,600 cycles. Future endurance tests of the CMC materials will be completed on the GE9X engine, Ingling says.
After producing eight engines to support the engine certification programme, another eight GE9X units will be delivered to Boeing to support flight testing of the 777-9 in 2018 and 2019. The ramp-up for production engines will begin in two years, followed by entry into service in 2020. Boeing has secured more than 300 orders for the 777X family, a respectable number for a widebody three years from entry into service. Meanwhile, CFM is evaluating the GE9X supply chain, with an eye to finding multiple suppliers for the same component.
“The CFM team has benefitted by sourcing from multiple suppliers; the GE9X supply chain team is working to ensure we have the correct sources for different production pieces,” Ingling says. “We are considering dual sourcing for some hardware and a rigorous quality inspection programme to mitigate risk.”
Source: FlightGlobal.com
