By Matt Benvie
The first jet engine used by the U.S. military was the result of a top secret project that took place in GE labs. Seven decades later, the Air Force is working with GE Aviation on the ultimate flying machine, and this time the partners are willing to talk about it. The “adaptive cycle” engine, as they call it, can automatically switch between the raw power of a fighter jet and slower, but more efficient flight desired by civilian airlines.
By marrying this adaptive architecture with a high-performance, heat-resistant core, this engine could achieve 10 percent higher thrust, 25 percent better fuel consumption, and 30 percent longer range, compared to the world’s most advanced military jet engines operating around the world today.
Top image: GE has been making jet engines for U.S. military since 1941, including the F110 engine for this F-16 that flew to the Paris Air Show from Aviano, Italy. Image credit: GE Reports/Adam Senatori. The adaptive cycle engine (above and below) could achieve 10 percent higher thrust, 25 percent better fuel consumption, and 30 percent longer range. Image credit: GE Reports
“To put it simply, the adaptive cycle engine is a new architecture that takes the best of a commercial engine and combines it with the best of a fighter engine,” says Jed Cox, who leads the Adaptive Versatile Engine Technology (ADVENT) project for the U.S. Air Force Research Lab. “So when I need high thrust, I can get high thrust. But when I don’t need high thrust, I can move into a super-fuel-efficient mode.” (See video below.)
Dave Jeffcoat, GE’s ADVENT project manager, says the design will “optimize the performance” of the engine for every part of the pilot’s mission. “We vary the pressure and bypass ratios mid-flight,” he says. “In takeoff conditions, the engine operates like a conventional fighter aircraft in a high-pressure ratio, low-bypass mode, allowing pilots to maximize thrust. But during cruise or loiter conditions, you don’t need that thrust, so we can transition to a high-bypass ratio, low-pressure ratio mode to be fuel efficient like a commercial engine. This adaptive feature of the design will deliver unprecedented performance capabilities to the Department of Defense,” he says.
The new design combines this “adaptability” with an additional source of air, called a “third stream of cooled air,” that can be used to further increase thrust, improve fuel efficiency, and dramatically reduce the amount of heat the aircraft has to handle.
That’s because the design, which was recently reviewed by propulsion experts from Lockheed Martin, Navy and NASA – in addition the Air Force and GE, includes the industry’s most expansive-ever use of heat-resistant materials called ceramic matrix composites, including the first rotating ceramic matrix composite parts in the turbine.
A turbine rotor with blades made from ceramic matrix composites (CMCs) after a test. The yellow blades are covered with an environmental barrier for experimental purposes. Image credit: GE Reports
“There have only been a few major leaps of this kind of change in the history of jet engine development,” says David Tweedie, manager of GE’s adaptive cycle engineering programs. “There was the leap from piston engines to turbojets, there was the leap from turbojets to turbofans. Now we’re making the leap from a conventional fixed cycle turbofan to a three-stream, adaptive cycle engine. We’re working with the Air Force to set the architecture and enabling technologies that will be critical to the warfighter for the next 20, 30, or 40 years.”
GE is also testing CMC blades inside commercial engines. Image credit: GE Reports/Adam Senatori
Matt Meininger, the Air Force Research Lab’s manager of adaptive cycle programs such as ADVENT and AETD said his team was “very proud of the partnership we’ve established with GE. In this case, it has developed a significant amount of trust and respect in the relationship, so we end up with a better product that’s going to allow for better defense of our country.”