GE’s Massive GE9X Engine Is Ready To Fly—At Last

The biggest aircraft engine ever built has been plagued by delays.

The long-awaited GE9X engine is finally flight-ready, after a lengthy and sometimes problematic development cycle.

The mammoth piece of machinery is the largest turbine aircraft engine in the world. It features 16 composite fan blades, each one more than 11 feet in diameter, housed in a 14.5 foot wide nacelle that is about the same size as a Boeing 737 fuselage. It can generate 105,000 pounds of thrust.

The engine also features a next-generation 27:1 pressure-ratio high-pressure compressor and a low-emission TAPS III combustor. The combustor and turbines are both made with a ceramic matrix composite material that is both lightweight and durable.

The blades and fuel nozzles are 3D printed. Metal AM removes complexity and waste from parts with complex geometries that would be difficult or impossible to build using traditional machining techniques. In the coming years, additive manufactured components will continue to reduce part counts by replacing assemblies with single components, which will help reduce weight and material cost while increasing fuel efficiencies of engines ready for flight. In fact, additive manufacturing has been integral in GE’s work on next-generation engines.

There’s no doubt the GE9X is a cutting-edge piece of machinery. But it seems as if the engine has taken forever to get to this stage. GE broke new ground in designing the massive engine—sometimes literally.

The overall pressure ratio of the GE9X is so high that existing test facilities weren’t adequate to test it. So GE needed to build an entirely new testing facility at its Evendale, Ohio, test center—with an investment of $120 million—to service the development of the engine. The A20 combustion test cell provides realistic combustor inlet conditions of 1,000psi and 1,475 degrees Fahrenheit—mirroring the conditions the combustor would find inside the engine itself.

“The combustor is in the heart of the engine, so it can be very difficult to take measurements in a fully assembled aircraft engine,” said Scott Herber, evaluation and test engineering manager at GE Aviation. “It can also be difficult to vary the parameters that govern combustion performance and efficiency in an aircraft engine.”

The A20 cell enables engineers to vary the conditions the combustor would see during operation and fine tune the combustion system to meet durability and emissions requirements. The facility also enables the collection of data that would be otherwise difficult or impossible to collect in a full engine test. That data has been used to not only adjust the combustion system, but also to better inform what hardware was needed around the combustor.

Alongside the A20 cell is the VESIL (Vehicle Energy Systems Integration Laboratory), which let engineers simulate and test various thermal systems and energy transfer mechanisms for the GE9X. This allowed them to determine the reliability of systems before flight tests and improve thermal efficiency.

Even after all the new infrastructure was built, a time-consuming process on its own, the engine ran into design problems. Flight testing had to be pushed back by the discovery of a turbofan design problem: the lever arms that move the variable stator vanes (VSVs) needed to be changed so they could properly modulate the air flow through the high-pressure compressor. The VSV arm problem was discovered during ground tests of one of the test engines running at full capacity: top fan and core speeds and maximum exhaust gas temperature.

The VSV arm problems were linked to exceedance loads on a section of the engine design. Fortunately, as the VSV arm is external to the compressor itself, GE has been able to resolve the flaw with a mechanical fix. Had the flaw been found within the compressor itself, it would have required a far more serious and complex redesign to change the air flow inside the engine.

The delays continued leading up to flight testing. The GE9X is so big that Boeing had to custom-design a large pylon to attach the engine to its 747 test plane with enough ground clearance under the machine.

Look at the size of that thing!

Look at the size of that thing!

The test plane’s other engines ran into problems too. The 747’s CF6 engines were found to have fan-case corrosion and limits on the HP turbine airfoils during routine checks which all 747s undergo every 600 hours.

Between the VSV arm issue and the CF6 problems, setbacks in the GE9X’s development threatened to push back the launch of the Boeing 777X—the largest plane Boeing has ever built, and the only aircraft big enough for the GE9X.

The 737 MAX crisis has also pushed back the public introduction of the massive superjumbo; Boeing decided it would be insensitive to reveal the new plan when the planemaker still had to resolve the problems of its existing plane.

Finally, however, the GE9X has finished its flight tests—320 hours worth—and the engines are now being mounted on 777Xs. Boeing’s aircraft is expected to begin its first tests later this year, and will enter into commercial service in mid-2020 as Emirates launches its 777X operations.

GE9X attached to the first 777X.

The GE9X is a new technological benchmark for the airline industry. Not only is it the biggest aircraft engine in the world—it is also the most fuel-efficient and quietest, and has the lowest NOx emissions, per-pounds-of-thrust jet engine ever produced by GE.

After being announced in 2012, the engine will enter into commercial use—at last— about a decade later. And it promises to dramatically push the limits of aircraft engines as we know them.

Read more about the GE9X-powered Boeing 777X at FAA Approves Folding Wings for the New Boeing 777X.