“The engine has margins, and history shows they are often needed,” he says. “Engines run hotter over time, so those reserves were a plus for us.”
Hess says P&W has a roadmap to increase the GTF fuel savings to 20-30% from 15% by the middle of the next decade. Some of that will come from bigger fans that increase bypass ratio to 15-18 from around 12 on the PW1000G, but P&W also plans to improve the core.
This will involve increasing the overall temperature of the engine and require new materials, says Adams. “We will drive thermal efficiency. Core technology will push overall pressure ratio beyond 60, which is the next threshold for this size of engine.”
“Temperature is a value trade with cash operating cost. We will not arbitrarily drive temperatures too high to gain performance but lose on maintenance cost,” he says. “We are in a good place with the current GTF.”
Referencing CFM’s first use of additive manufacturing, in the Leap fuel nozzle, Hess says “On entry into service on the CSeries, our engine will have 25-26 parts that are additive.” The PW1500 for the CSeries will also have “around 200” composite parts, he says.
On CMCs in engines, used for the first time in the Leap, Hess says P&W had a CMC part in the F135 engine for the F-35 Joint Strike Fighter, “but we decided to replace it with an alternative composite material for lower cost and risk. We are at least as capable in composites as the competition.”