Half a century after the world’s first 40,000-lb.-plus-thrust high-bypass turbofans entered development for the emerging widebody era, studies are underway for a new generation of powerplants in the same thrust bracket.
But now, unlike the 1960s—when General Electric, Pratt & Whitney and Rolls-Royce had very specific power requirements for the Boeing 747 and the new trijets—the picture is far from clear. While it is increasingly obvious that new engines will be needed for whatever aircraft emerge from the amorphous Boeing middle-of-the-market (MOM) study, it is equally obvious there will be no easy answer. What may have begun as a relatively straightforward 757 replacement study is evolving into a more complex beast with tentacles reaching down into the A321/737 sector and up into A300/767 territory.
Engine makers guess the power needs, at least for the initial MOM member, will be in the 40,000-50,000-lb.-thrust bracket; beyond that the design space remains wide open. “This market is anywhere between 100 and 250 seats,” says Rolls-Royce Aerospace President Tony Wood. “It is quite clear new-generation aircraft are overlapping. The market is changing and becoming more fragmented, and it may well be a one-part solution is less likely in the future.” For Rolls, which effectively exited the single-aisle business with the sale of its stake in International Aero Engines and the V2500, the MOM could be a priceless new market opportunity.
Rolls is targeting whatever emerges from MOM with a new family of engines under development as part of its two-phase evolution strategy from today’s Trent XWB. The first engine, dubbed the Advance, is aimed at entry into service in 2020 and will have a bypass ratio in excess of 11:1, an overall pressure ratio of more than 60:1 and a fuel-burn level at least 20% better than the Trent 700. The second, more ambitious follow-on concept—called UltraFan—could be ready for service from 2025 onward and is targeted at a fuel-burn improvement at least 25% better than the Trent 700. The UltraFan will incorporate a fan drive gear system that powers a variable pitch fan and is outlined with a 15:1 bypass ratio and overall pressure ratio of 70:1.
Boeing 757 successor studies have sparked interest in next-generation engine concepts.
The two-pronged strategy is scaled and designed to incubate a family of engines capable of powering everything from large single-aisles to the largest widebody. “We are making sure we are credible to do that,” says Wood, who adds that with the Advance-UltraFan plan “we are moving fast. We are in the demonstration mode and we have to make sure we are fast enough to get these technologies developed.”
Rolls’s own studies indicate the sweet spot will be “the high end of the 757 or the low end of the widebody. That is our big target area,” says Eric Schulz, president of Rolls-Royce large civil engines. “There has been a clear push to the right [in aircraft size] which is motivated by capacity in emerging markets and overall constraints in the big airports. So we expect to see a natural transition into the high end of the market.” Rolls’s plan is to be ready for whatever comes. “It is all about the technology,” he adds.
For Pratt & Whitney, MOM could be the opening it needs to grow the geared turbofan. With the baseline PW1000G program in full swing and an orderbook for around 7,000 engines across three main variants, Pratt senses a new opportunity. “It will evolve over the next year to 18 months,” says President Paul Adams. The provisional timescale is also open to conjecture, but “we are looking at entry into service around the 2023-28 period,” he adds.
While Rolls and Pratt have signaled high interest in the potential new market, the message from General Electric is more muted. Challenged with the successful production and delivery of its record-setting order backlog for CFM56, Leap, GEnx and GE9X engines, GE Aviation President David Joyce says the emergence of the next-generation middle of the market is simply not a priority for the company right now. However, he does acknowledge “the thrust class alone will determine it is a new engine. We don’t have an engine in the portfolio that fits this thrust class. Will it take a new development program? Yes. I’d argue that certainly there’s a market there—we are working on technologies for a 757/A300 replacement. But my primary focus is on executing delivery on what we have already committed to. We have a huge, huge, huge execution challenge ahead of us.”