Two years ago, when Boeing decided to build the world’s largest twin-engine jet capable of routinely crossing more than 9,000 miles on a tank of fuel, it needed a powerful engine to go with it. GE engineers solved the problem for the plane maker by proposing an engine so large it could swallow a subway train through its 11-foot-wide air inlet.
When completed, the engine, called GE9X, will be the largest jet engine ever built. It’s design became possible because of a high-stakes engineering wager that paid off 20 years ago this month.
Until the early 1990s, all jet engines were made from steel and titanium. But GE designed an engine with large fan blades from what was essentially plastic.
To be sure, this wasn’t the stuffof disposable cutlery. The team focused on a strong and light material calledcarbon fiber composite. It’s made from stacked sheets of carbon fiber fabric and a toughened epoxy, kind of like a high-tech crepe cake.
If the idea worked, the GE team reasoned, the lighter composite blades would shave hundreds of pound off each engine, and allow engineers to design a bigger machine with more thrust. “But it was a really tough sell,” says Nick Kray, a consulting engineer for composite design at GE Aviation, who joined the effort early on. “People weren’t initially so hot about the idea. Nobody had tried this before.”
The teamwasn’t starting completely from scratch. In the 1980s, the company developed the experimental GE36 open rotorengine (see above). It used carbon fiber composite blades in an unusual hybrid design thatcombined features from turbofan and turboprop engines. Although the enginedemonstrated fuel savings of more than 30 percent compared withsimilar-sized conventional jet engines, it didn’t catch on.
This GE90 engine had to survive encounters with golf ball-size hail. Top image: Blade designer Paul Izon next to a blade for the GE90 engine.
Back in the lab, challenges popped out behind almost every test. Typical titanium blades absorb energy and bulge when they hit an obstacle, say, a bird. But ordinary composites can delaminate and break. “We didn’t know how this new material would respond to stress,” Kray says.
The team ranhundreds of intensive tests simulating bird strikes, rain, snow and hail stormsat GE’s jet-engine boot camp in Peebles and the Wright Patterson Air Force Base, both in Ohio. “We’d test almost daily and make changes based on what we learned,” Kray says. “The results gave us enormous confidence in the material when we saw how durable it was.”
Brian Rowe served as CEO of GE Aviation and led the GE90 development. The FAA certified the engine in February 1995.
By 1993, the team had the right material and blade design, but they were far from done. Now they had to produce it. GE Aviation decided to team up with its European jet engine partner Snecma. The French aerospace company was experienced in making in high-tech composites. They former a joint-venture called CFAN and built a new composites factory in San Marcos, Texas.
Even with the help, making the blade was a hard climb. “The manufacturing of composites remains a manual process,” Kray says. “The material goes through chemical changes and tends to move around. We had to learn how to get it right.”
The workers inspect every single blade with X-rays, ultrasound, laser and other tools for defects. Initially, only 30 percent of them passed. (The current yield is about 97 percent.)
The GE90-115B is currently the world’s most powerful jet engine.
The Texas workers weren’t learning about composites alone. GE also had to explain the material to regulators, and even Boeing. The plane maker wanted to use it on its 777 long-range jet, and the first one was scheduled to leave its plant in 1995. “On top of everything, we were racing against time,” Kray says. “It was a very steep learning curve.”
Ultimately, the wager has paid off. Even though the engine had a fan with 128 inches in diameter, the composites shaved 400 pounds of the machine. The Federal Aviation Administration certified the engine, called GE90, and the composite blades in February 1995. “The engines essentially opened the globe up to incredibly efficient, twin-powered, wide-body planes,” says David Joyce, president and CEO of GE Aviation.
The engine wasn’t shy about showing its power and grace. In December 2002, the GE90-115B version of the engine entered the Guinness list of world records as the most powerful jet engine ever built, generating thrust in excess of 127,000 pounds – more than early space rocket engines. In 2005, a GE90-powered Boeing 777 set another world record, this time for distance traveled non-stop by a commercial jetliner. The plane covered 11,664 nautical miles between Hong Kong and London in 22 hours and 42 minutes. In 2007, the Museum of Modern Art in New York included the curved composite blade in its design collection.
The GE90 engine is blowing off rocks near the runway at GE’s Flight Test Operation Center in Victorville, Ca.
Even after 20 years, GE is still the only jet engine maker with engines using composite blades in service. Kray and other engineers are currently working on a fourth-generation blade for the GE9X engine for the 777’s successor, Boeing 777X. That plane will be the largest and most efficient twin-engine jet in the world.
New advances in composites technology have allowed the team to make an even bigger engine – the GE9X’s fan diameter will be 134 inches – with fewer thinner and stiffer blades. (The GE9X will have just 16 blades, compared to 22 on the GE90.)
“Next-generation composites will go even further,” Kray says. “We are never going back to metal.”
A rendering of the fan for the GE9X. It will have only 16 blades made from fourth-generation carbon fiber composites.The silver tips of the blades are made from titanium.
Image credits: GE Aviation