The technology stakes are high for the GE9X engine that will power Boeing’s new 777X twinjet, but GE Aviation believes its big bet on the weight savings to be delivered by unprecedented use of composites is about to pay off. The U.S. engine maker, which currently holds orders for some 600 of the engines, is leaving nothing to chance and, with more than two years of technology maturation behind it, the company is now stepping up its test program en route to certification in 2018.

On July 10, GE announced the appointment of three “participants” in the GE9X program: Japan’s IHI Corporation; Safran subsidiaries Snecma and Techspace Aerospace from France and Belgium; and Germany’s MTU Aero Engines. Collectively they will account for around 25 percent of the project.

IHI will be responsible for the design and manufacturing of various components in the low-pressure turbine and the fan mid-shaft. The company is already a GE partner in the CF34, GE90, GEnx and Passport engines.

France-based Snecma will handle the design and manufacturing of the 3D-woven composite forward fan case and the turbine rear frame, as well as supporting GE with the composite fan blades through its CFAN 50/50 joint venture.

Techspace Aero from Belgium is taking on the design and manufacturing of the GE9X low-pressure compressor, as well as manufacturing the fan disk. The company is also a partner in the CF34, GEnx and Passport programs.

MTU is designing and manufacturing the turbine center frame. It already participates in the F110, CF6, GP7200 and GEnx programs.

The new 100,000-pound-thrust turbofan is expected to deliver a 10-percent reduction in fuel burn compared with the GE90-115B engines on the existing 777-300ER. Also promised is a 5-percent improvement in specific fuel consumption over rival widebody engines by 2020.

GE9X Fan Tests

Having run a compressor test rig earlier this year at the Massa, Italy, facility of GE subsidiary Avio Aero, GE and Boeing have now started testing a one-fifth-scale version of the GE9X fan using an indoor test cell fitted with microphones to measure the acoustic signature of the fan. “We’re running a couple of different configurations of the fan blade and the OVGs [outer guide vans] to understand the mechanics and operability of the fan blades,” explained Bill Millhaem, general manager of the GE90 and GE9X programs.

The GE9X’s composite fan blades are a major part of the equation. GE has been using these for the past 20 years and by 2020 expects to have logged more than 100 million flight hours with them.

GE has reduced the number of fan blades from 22 on the GE90-115B to 16 and these are thinner and 20-percent lighter thanks to the use of a second-generation ceramic matrix composite (CMC). This combined with a wider chord has boosted the performance of the fan. Between the lighter blades and the use of composite case technology developed for the GEnx engine, GE aims to take about 1,000 pounds of weight out of the new engine.

Later this year GE will run tests on a GEnx engine fitted with a full suite of CMC components destined for the GE9X. The engineering team has also started running some tests on the TAPS III twin annular pre-swirl combustor, which is a major contributor to the engine’s improved fuel burn, as well as to reductions in noise and nitrous oxide emissions.

This is the third generation of the TAPS technology and it features a mixer designed to get more air into the combustor, resulting in an improved temperature profile, lower emissions and greater aerodynamic efficiency. This lean-burn combustor also features in the new Leap-X engines being developed by the CFM International joint venture in which GE is partnered with France’s Snecma.

Around the middle of next year, GE expects to run a full core test that will allow it to complete the long technical maturation process. This will lead into the final design phase ahead of a first full engine test in 2016 and flight test in 2017.

Overall, the technical maturation work for the GE9X will have taken roughly twice the time that was dedicated to the same phase of the GEnx program. “Had we simply taken a GEnx engine and stretched it to 100,000-pounds thrust, we would have got a 5-percent improvement in fuel burn, but Boeing demanded 10 percent so we needed to do more to achieve the additional 5 percent,” explained Milhaem. Another priority for GE is that the engine achieves a mature level of reliability from initial service entry.

“We took a big bet on composite fan blades and by 2020 we will have logged more than 100 million flight hours with them in total,” said Milhaem during AIN’s visit to GE’s Cincinnati, Ohio, headquarters last month. “It’s been a remarkably durable improvement and this [the GE9X] is a chance for us to take the next big step with a new carbon fiber system and drive some incremental improvements.”

The improved aerodynamic performance of the GE9X blades has resulted in a 27:1 pressure ratio in the new engine’s high-pressure compressor, contributing to an overall 60:1 overall pressure ratio. By comparison the GE90’s pressure ratio is 19:1 and that of the GEnx is 23:1.

Milhaem explained that increased computing power has allowed the GE team to have a better understanding of how the various engine shapes and components would perform even before they were made.

The 350 hours of compressor tests at Massa yielded better than expected performance. Further adjustments will now be made to the compressor and Milhaem believes that a bit more performance improvement can be achieved.

GE is currently building a new combustor facility in Cincinnati that will allow it to do higher pressure and temperature testing from next January. For the GE9X combustor fuel nozzle tips, the company has used a new additive manufacturing process that allows engineers to more quickly and efficiently conduct a trial-and-error approach to perfecting the design.

For the GE9X, the use of CMCs has been extended into the hot section of the engine. “It is about one-third of the weight of metal, has twice the strength and about 20 percent more temperature tolerance, which is a huge margin in this part of the engine,” Milhaem explained.

GE’s Farnborough International Airshow display (Pavilion P1-5) features a 3-D video depicting the operation of the GE9X. The company’s new pavilion also includes a GEnx engine, and examples of the new composite fuel nozzles and 3-D printing production techniques.

GE Engineers Push The Boundaries Of Powerplant Efficiency

Much of the focus of longer-term research and development work at GE is on improving both the thermal and propulsive efficiency of powerplant, according to Chris Lorance, the company’s chief technologist for commercial engines. Efforts to boost propulsive efficiency have mainly been focused on designing more efficient fans by reducing the numbers of blades and boosting bypass ratio (see main article).

“Thermal efficiency is a key factor [in improved engine performance],” he told AIN. “So we’re working on better cooling flow reduction and mitigating temperatures through cooling, as well as improved aerodynamics through the core. Innovative cooling technology is allowing us to heat air but also achieve good durability for components.”

Meanwhile, GE is continuing to explore the potential of an open rotor engine design through a joint program backed by NASA. “We believe we can run these engines at higher Mach numbers than previously thought,” Lorance said. “Regional narrowbody aircraft would be able to fly nearly as fast as a conventional turbofans and this is probably the most attractive application [for an open rotor engine].”

GE is preparing to conduct further tests to ascertain the overall performance from the design, as well as its acoustic characteristics. Meanwhile, it is also in contact with aviation regulators to clarify the terms under which such a powerplant would be certified.

Another technology niche that GE is increasingly probing is the use of hybrid electric powerplants that would allow aircraft to take off with a conventional gas turbine and then cruise on a battery. The batteries could be charged from the turbine engines, as with the all-electric power on the Boeing 787. Lorance acknowledged that more work needs to be done to make batteries lighter and added that GE is already in talks with regulators about the use of electric motors.

Military Fuel-flow

With the backing of the U.S. Air Force, GE is continuing its work on adaptive cycle engine technology. Dan McCormick, GE’s lead technologist for military engines, explained that its adaptive versatile engine technology (Advent) program is aimed at achieving a generational shift to a three-stream engine with significant changes in the way air flows through. “The more air you can get into the outer zone of the engine, the more efficient it will be and for combat aircraft the goal is to achieve high thrust when it’s needed and more fuel efficiency when it is not needed,” he told AIN. The program has set the ambitious target of achieving a 25 percent improvement in fuel efficiency over current generation military aircraft engines, for possible application in the coming sixth-generation fighters.

GE, which this year is investing almost $1.25 billion in research and development, is also developing a new version of its GE38 turboshaft engine for helicopters. Next year, it will be stepping up testing for the future vertical lift program.