While focused on delivering geared turbofan (GTF) engines for the new Mitsubishi MRJ and Bombardier C Series, Pratt & Whitney is turning its attention to the wider applications of a technology that offers a 12- to 15-percent improvement in fuel burn by allowing the engine fan and low-pressure turbine to operate at optimum speeds.
Robert Keady, senior v-p sales P&W Commercial Engines & Global Services, told reporters here in Dubai yesterday that the GTF unit (which weighs between 350 and 300 pounds) would be of a different design for applications to larger engines beyond the 30,000-pound top thrust that it has so far tested with its PW6000-based demonstrator engine. “We may change the gearbox and go from a 3:1 to a 4:1 gear ratio,” he admitted.
The present fan drive gear system (FDGS) has a sun gear and five star gears driving the surrounding ring gear giving a two-thirds speed reduction to the fan and allowing the low-pressure (LP) system to run 2.5 times faster.
However, Keady said the area with the most potential sales would be a 20,000- to 30,000-pound-thrust engine for next-gen narrowbodies, although in that market segment P&W currently operates through its International Aero Engines (IAE) joint venture with Rolls-Royce, MTU and Japanese Aero Engines Corp. “When looking down the road we have the opportunity to improve the V engine but the demands for the future aircraft–30 to 40-percent improvement–are not achievable by the V, so I think the GTF is probably the path to bring that kind of step change.”
Keady also said that beyond entry into service of the GTF on the C Series in 2013, P&W would continue to target fuel burn improvements averaging 1 to 1.5 percent a year, in line with recent trends. “We anticipate that we will continue with improvements in efficiency by continuing to improve bypass ratio from 11 to 12.”
“The other area we would work on is the overall pressure ratio of the core, with higher pressure ratio high-pressure compressor stages, and we would continue to work on advanced materials. But we don’t want to take technology steps that would bring a lack of reliability.” P&W’s tests on the demonstrator core have shown that the gearbox is reliable and runs at 99 percent efficiency. Tests on an Airbus A340-600 saw it being flown “all over the flight envelope,” said Keady, including rejected takeoffs, cold starts, maximum angle of attack and 2.1-g maneuvering.
“Now we have built our first [actual] core and will start testing this year in Canada. We’ll be progressing to full engine testing next year,” he said. Minimizing maintenance cost is a particular priority for the design, said Keady. This includes 25,000 life-limited parts to synchronize maintenance periods and a reduction of 1,500 airfoils over conventional designs.