Compressor Performance Key To PWC’s New Turboprop
Despite some vacillation by ATR and Bombardier, who are still studying the form their respective 90-seat regional airliners might take, development of Pratt & Whitney Canada’s new turboprop engine continues on a “critical path” to an expected launch next year, according to Richard Dussault, company vice president of marketing. Called the Next Generation Regional Turboprop (NGRT), the engine would feature an all-new compressor, a miniaturized version of Pratt & Whitney’s patented Talon combustor and, perhaps, an eight-blade propeller, all meant to contribute to a 20-percent improvement in fuel efficiency, as specified by Bombardier and ATR.
Approaching the end of what Pratt Canada calls Phase 1, which essentially involves component-level testing, program engineers just finished what Dussault called the inlet section, during which they tested the first two stages of compression. Dussault said the results proved satisfactory, allowing the company to ship the first complete compressor to Germany’s MTU, where schedules call for engineers to start the next round of testing next month. By the third quarter of this year the company expects to have collected enough data from 500 points of instrumentation on the compressor to validate its expected performance.
Based on entirely new architecture using mostly conventional materials, the compressor–more than any other part of the engine–will dictate whether or not the company can achieve the 20-percent fuel efficiency improvement being targeted, Dussault explained.
“We’re very comfortable with all the hot-end turbine technology that we’re importing from the geared turbofan and next-generation product family, so at that point we’ll be able to start making firm customer commitments on performance and program deliverables,” he said.
Meanwhile, the company will conduct preliminary testing on a version of the low-NOx Talon combustor for the NGRT, he added. “As you can imagine, the NGRT is much smaller than a geared turbofan in terms of core flow and core size,” said Dussault. “So the cooling flows become more challenging, because the [cooling] holes get smaller…and tougher to manufacture, to manage and to make sure you get everything just right.”
In terms of the total engine package, “just right” could mean different things to different companies. The Pratt & Whitney PW150A used in today’s Bombardier Q400, for example, produces 5,071 shp, while the PW127M on the ATR 72-600 generates just 2,750 shp. Although the Q400 seats about 10 more passengers, it also flies as fast as 360 knots–almost 100 knots faster than the top cruise speed of the more fuel-efficient ATR 72-600.
Dussault quoted a “sweet spot” for a 90-seat turboprop of between 300 and 325 knots, a span that virtually splits the difference between the current Bombardier and ATR products. Given the engine company’s fuel-burn targets, this would require an engine that produces in the range of 5,000 to 7,000 shp, although the preliminary design allows for “growth” to as much as 8,000 shp.
In any case, the company is unlikely to offer two distinct engines, said Dussault. “It’ll be very important to size the engine right,” he said. “You want an engine that’s as small as you can get it, but [that can] still attain the performance objective at the aircraft level. That’s the next logical step.”