At nearly 13 feet in diameter, the GE9X is the largest jet engine ever built. It is wider than the fuselage of a Boeing 737. Or, as the publicists at General Electric put it, if Kobe sat on Shaq's shoulders, the two of them could easily walk through it.

Like we said. It is a really big engine.

The 20,000-pound turbojet that GE is testing at its proving ground in Ohio draws air faster, at greater volume, and with superior efficiency than the former top dog, the GE90-115B. A pair of them could suck all of the air out of a space the size of Yankee Stadium in 13 minutes flat.

GE designed the behemoth specifically for the Boeing 777X widebody airliner expected to take flight in 2020. The engine uses 3-D printed components, composite materials, and redesigned fan blades and air routing to deliver a staggering 10 percent increase in fuel efficiency without sacrificing power or reliability. That's a Herculean feat in a field where engineers would step over their own mothers for a one percent bump.

This engine actually produces less power than the GE90-115B (105,000 pounds of thrust compared to 115,000 pounds). But it's not only far more efficient, it's the quietest engine GE's ever made (measured per pound of thrust). The GE9X fits easily within the FAA's "Stage 5" noise rules, which kick in next year.

"The GE90 helped enable Boeing’s 777-300ER to have a dominant international route market position for the past 15 years," says Richard Aboulafia, an aviation analyst with the Teal Group. The GE9X will allow "the 777-X series to maintain that market dominance for another few decades. It will likely be the largest, most powerful, and most advanced large turbofan built for some time."

Size Matters

A commercial turbofan engine is essentially a jet engine surrounded by an enormous fan. The jet generates some thrust, but it's there primarily to keep the fan spinning. The fan draws in air, speeds it up, and fires it out the back, providing most of the engine's power.

Bigger is better here mostly for the sake of efficiency and noise. A larger fan draws more air with less energy, as long as you're mindful of the aerodynamics and keep weight to a minimum. Larger fans make for quieter engines, too, because they distribute airflow over a greater area. GE wants to send as much air as possible around the engine’s core rather than through it. Engineers call that bypass flow. Bigger fans make it possible. The GE9X boasts a bypass ratio of 10:1, compared to the old engine's 7.5:1.

(This also explains why fighter jets are so loud: They’re basically engine cores with wings, and their engines use small bypass ratios so they fit within smaller airframes. This also is good for power but terrible for fuel efficiency.)

If accomplishing this was as easy as making the blades longer and the air inlet bigger, engineers would have done it ages ago. But larger fans require lighter blades so the increased performance isn't offset by decreased fuel efficiency. And everything else must be robust enough to handle higher internal temperatures and pressures without adding any more weight than necessary. Keeping all of these things in balance required some advances in materials and designs.

When the GE9X takes off, it will cast a bigger shadow on the tarmac than anything that’s come before.

GE engineers designed carbon fiber blades to minimize weight, and some aerodynamic tweaks to increase their ability to withstand high-speed airwaves during flight. “We modeled huge blades to pull massive amounts of air into the engine while operating at low noise levels,” says project leader Chuck Jackson.1 “Traditional titanium blades at this size would have added too much weight.”

The fan has 16 blades, down from 22 in the previous model, further decreasing weight and increasing efficiency. The case surrounding them uses composite materials as well, cutting 350 pounds.

The intricate nozzles that precisely regulate the flow and delivery of fuel into the combustion chamber rival the human ear in complexity, and GE relied upon 3-D printing—a process it calls "additive manufacturing"—to manufacture them with the precision tolerances required to maximize performance and efficiency.

The GE9X's record pressure ratio of 27:1 (compared to 19:1 for the GE90-115B) raises the temperature of the air about 100 degrees Fahrenheit. That boosts efficiency but is tough on components. For greater heat resistance (and lower weight), GE's engineers used ceramic matrix composite materials for parts of the combustor and turbine, where things get hottest.

A suite of analytics capabilities will allow airlines to monitor and predict maintenance needs, minimizing downtime for service and repairs. Upgraded processing capability and new sensors will collect this data and communicate it to the service managers and GE’s cloud-based computing platform for analysis.

Aviation moves slowly, and the new engine has a lot of testing to go through before it’s production ready. That involves gulping down buckets of sand, hundreds of gallons of water a minute, ice balls, and dead chickens. But once it’s proven itself, the new power unit will cast a bigger shadow on the tarmac than anything that’s come before it.

1Post updated at 12:26 EST on Friday, April 29 to correct Chuck Jackson's name.