Mitsubishi Picks GTF for Future RJs

Dubai Air Show » 2007
November 8, 2007, 2:30 AM

The news that Pratt & Whitney had beaten Rolls-Royce and General Electric in the competition to power the new Mitsubishi Regional Jet (MRJ) was received in the company’s Connecticut headquarters with more than the usual celebration. It meant that Pratt & Whitney had secured a launch order for one of the most important engines it has ever developed.

With the Geared Turbofan (GTF), designed to cut fuel burn by up to 10 percent and noise by half compared to the best engines available today, P&W is putting on the line its future in the medium-sized commercial engines business.

According to Bob Saia, vice president for next-generation products at P&W, the campaign to sell the GTF to Mitsubishi was launched in February– well before the planned first run of the development engine in November. “This is quite normal in any engine program. We’ve built up a huge amount of data already in 15 component rig tests and we’ve run three demonstrators during the last decade, so we already have a lot of experience.”

The development engine, the core of which is based on the existing PW6000 engine, is due to fly on the company’s Boeing 747 test bed in June 2008 and will remain in flight test until November. “This will provide a huge amount of data which will be fed into the design of the actual engine for the MRJ,” said Saia.

The components that differentiate the GTF from normal turbofans–the fan, low-pressure compressor and the fan drive gearbox connecting the low-pressure compressor to the fan–have been subject to an intense test program. “We began testing the fan gear drive system in July on a special rig at Connecticut,” Saia told AIN. This crucial test will continue until next July, “but we’ve already validated key elements such as the lubricating oil temperature. We’re very pleased with the results, which match exactly with our engineers’ predictions.”

P&W said it is “working with all of the original equipment manufacturers” on potential applications for the GTF. “We’ve talked to Airbus, Boeing, Embraer, Bombardier and even Sukhoi,” said Saia. “We’re talking about using the GTF as the main architecture for the next generation of aircraft.”

The engine for the MRJ will be delivered at a rating of 15,000 pounds thrust for the 70- to 80-seat MRJ70 and at 17,000 pounds for the larger 86- to 96-seat MRJ90. P&W is working on a family of GTF engines running up to the same 33,000 pounds thrust as the existing International Aero Engines V2500, although in testing with a PW2000 in 1998, using a slightly different design of gearbox, the engine reached 40,000 pounds thrust with no difficulty. “We’re making sure we’ve got the maximum likely thrust of the new generation of single-aisle aircraft well covered,” said Saia.

The P&W executive rebuffs critics who say the GTF is heavier than regular turbofans. “My understanding is that for the MRJ our GTF was actually lighter than the competition,” said Saia. This is because the GTF will employ an advanced core with fewer stages and blades. The low-pressure turbine, for example, under development by P&W GTF partner MTU, will have 900 fewer airfoils than the similarly sized V2500, with three stages instead of the usual five.

P&W is also working on a lightweight 18-blade wide-chord, swept tip fan, which will be driven at two thirds the speed of conventional fans via the Avio-developed gearbox. Saia declined to reveal the exact nature of the fan blade material, beyond saying, “It is metallic, it is new and we’ve had very good results to date.” An all-composite backup version is being developed with advanced propeller manufacturer Hamilton Sundstrand. The fan is the same 56-inch diameter as those of the competition, Mitsubishi having required all three contestants to come within the same engine diameter limitations because of wing and landing gear characteristics.

Next on the list of potential applications is the long-awaited Bombardier C Series, for which a larger, 23,000-pound-thrust engine is needed. This would use exactly the same core design, but scaled up to provide the extra thrust.

A decision on launching the C Series is due next year. Another victory for the GTF would secure the credibility of the geared fan concept, leaving P&W in a far stronger position to secure a place aboard the aircraft that will eventually replace the Airbus A320 and Boeing 737 families.  

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