Flight-testing, first on the CSeries and then of the A320NEO engines, has resulted in deletion of the variable-area fan nozzle (VAFN), which Pratt had thought would be needed to provide enough flutter margin for the large-diameter fan.
But Hess says the latest hybrid-metallic fan blade has much better flutter characteristics than expected and sufficient margin to eliminate the VAFN “and get rid of the complexity and weight.” NEO test engines are now flying with the nozzle locked, but design changes will delete that feature from production engines.
“The engine is proving itself in flight-test,” Hess says. Meanwhile, Pratt has plans in place for a next-generation GTF to extend the fuel-burn benefits from the current 15% reduction to 25% in 10 years.
The initial PW1000G series tackles propulsive efficiency by introducing the geared fan. The next step will focus on improving thermal efficiency through “higher pressure ratios, high OPR [overall pressure ratio] cores, better materials and coatings,” he says.
Key to this will be the U.S. Air Force Research Laboratory’s Adaptive Engine Technology Demonstration (AETD) program, under which Pratt will run a variable-bypass combat engine demonstrator by 2016. AETD “will demonstrate technologies for military and civil engines and give us our next-generation core and materials,” Hess says.
“AETD is strategically important,” he notes. “We are getting investment help from the government, but we are putting a lot of our own money into it also.”