GE Aviation has completed assembly of the first GE9X test engine at its Peebles, Ohio facility where it will shortly begin ground runs of the 100,000lb-thrust (445kN)-class powerplant for the Boeing 777X.

“The engine is assembled, it is just a matter of adding lots of instrumentation,” says GE9X programme manager Bill Millhaem. Tests will begin “soon”, he says, although declines to offer a precise date.

The GE9X features a basket of advanced technologies as GE strives to reduce weight and improve engine performance to deliver a 10% reduction in specific fuel burn over the current-generation GE90.

These include use of ceramic matrix composites (CMC) on the inner and outer combustor liners, and stage 1 and 2 nozzles and stage one shroud in the high-pressure turbine. CMCs are significantly lighter, stronger and more heat resistant than the metal components they replace, saving weight and allowing the engine to run hotter and more efficiently.

GE last year performed 2,800 cycles of testing on the majority of the CMC components installed in a GEnx development engine and will in the next two months begin another 3,000-cycle evaluation, this time adding the stage 1 nozzle absent from the previous test effort.

The CMC parts have so far performed “phenomenally”, says Millhaem. “We took it apart and you could have steam cleaned the combustor liners and put them back in an engine.”

Additional dust ingestion tests will be conducted “for some of our customers in the Middle East” to evaluate the effects of abrasive sand on the CMC components, he says.

GE is also using additive layer manufacturing (ALM) techniques on the GE9X. It is producing the stage 5 and 6 turbine blades from titanium-aluminide via an electron-beam metal sintering process, while more traditional ALM is employed to make the fuel nozzle tips in its TAPS III combustor.

However, Millhaem says that two additional unspecified components are now being made via ALM – one “purely for weight saving” and the other to simplify an otherwise “very, very challenging” production process.

Additional changes could still be made to the design in the year between the first engine run and the arrival of the next test powerplant, he says, although GE aims to have a “very stable configuration” for the certification and flight-test phase of the programme.

The maiden sortie of the GE9X, using a company owned 747-400 flying testbed, is due to take place in mid-2017. Engine certification is scheduled for October 2018.

Previous trials of the high-pressure compressor, which features an industry-leading 27:1 pressure ratio, have also validated its performance, says Millhaem.

“The first build exceeded our pre-test predictions and the second build allowed us to incorporate some minor modifications to get an incremental specific fuel-burn improvement,” he says.