While ATR and Bombardier continue to vacillate over plans to introduce a new 90-seat turboprop, Pratt & Whitney Canada keeps moving forward with an engine it believes will deliver a 20-percent fuel burn improvement over existing engines in the 5,000- to 7,000-shp range by the turn of the decade. Dubbed 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 likely an eight-blade propeller.
Hoping to finish design work involving the high-pressure compressor that would form the primary basis for the improvements this year, the engine company continues to closely guard the design details of that fundamental component, however.
Speaking with AIN during a recent media event at the headquarters of parent company Pratt & Whitney in East Hartford, Conn., Pratt & Whitney Canada vice president of marketing Richard Dussault took care not to reveal anything not already made public by the company in terms of the number of stages in the compressor, its pressure ratio or any unique design elements. He did confirm that the overall engine design incorporates an impeller, or centrifugal compressor, rather than an axial compressor. Testing on the impeller “at the component level” has taken place at program partner MTU in Germany, said Dussault, as has testing on the first stage of the compressor near the engine inlet to verify what he called the entry condition to the compressor.
Now embarking on Phase 2 of testing, the company expects by the end of this year to have completed design work on the compressor at MTU, said Dussault. “By the end of the year we’ll be fully ready, proven…,” said Dussault. “Today all the signals are extremely good; we want to complete the design work and the testing work to make sure that we further optimize and maybe in the end when we make a guarantee to an OEM customer we’ll be able to have very solid data on which to base ourselves and make the commitment to a full engine program.”
This year not only is Pratt working on optimizing the compressor, noted Dussault, but the company has spent more time with the airframers in an effort to define system architecture and execute noise and weight trades.
“The propeller is a great example,” he said. “Obviously the bigger the propeller the more…you need to sort of bring the engine outboard a little bit. So there is some design onto the aircraft that they need to take into account in terms of wing design, empennage design.” The company also continues its studies into bleed air requirements for air conditioning and pressurization and the more demanding electrical needs inherent in modern aircraft designs.
“When we combine all that, we can work trades,” said Dussault. “Once we have the core of the engine well understood [we can start] sort of doing the packaging and optimizing the packaging to make the engine as small as we can and the nacelle small because that reduces drag.” Such trades need to result in an engine that can power an airplane between 300 and 325 knots over an optimal range of between 200 and 400 nm, said Dussault, whose speed “sweet spot” for a 90-seat turboprop virtually splits the difference between today’s Bombardier Q400 and ATR 72-600. 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.
According to Dussault, the airlines have already spoken loudly in favor of a 90-seat turboprop; whether or not the NGRT materializes as a production engine hinges totally on the willingness of the airframers to commit the needed investment.
Although confident in the technology, Pratt Canada won’t execute a full launch of the program and start building prototypes until an airframer commits, said Dussault. “We need to have the right winning conditions for launch, for making [such] a huge investment,” he concluded.