It may be ‘back to the future’ in next-generation jet engines

Farnborough Air Show » 2006
November 27, 2006, 10:25 AM

CFM International is including a contrarotating ducted fan engine in studies of concepts that might provide the quantum leap in fuel efficiency, noise reduction and emissions being demanded for the next generation of single-aisle aircraft.

The engine would draw on lessons learned by CFM partner General Electric during the unducted fan (UDF) program carried out with NASA in the early 1980s, which demonstrated specific fuel burn reductions of up to 20 percent.

Meanwhile, Pratt & Whitney president Steve Finger said he “does not rule out” offering its geared turbofan (GTF) next generation single-aisle contender for the coming generation of 70- to 130-seat regional jets. “The GTF will be the right product for a wide range of applications,” he added.

P&W also announced that MTU Aero Engines, Avio, Volvo and Goodrich had become strategic partners “for continued development of key GTF technologies.” MTU will work on a common, scalable core; Avio on the advanced gear drive system, described by P&W as a “critical part of GTF technology” and on the flight test demonstrator; and Volvo on the turbine exhaust case. Goodrich will develop the specialized nacelle system required for the GTF.

Retiring P&W commercial engines president, Steve Heath, confirmed that P&W had talked to 25 airlines about the GTF concept, including, most recently, the Star Alliance group. He admitted there had been “some concerns” over P&W’s geared turbofan approach, but claimed that was “largely because we need to explain to them very clearly what the advantages are.”

A ground test of a flight-worthy GTF is planned for the third quarter of 2007 with flight testing in 2008 aboard P&W’s Boeing 747 testbed. Heath said, however, that “my fondest dream would be to convince the aircraft manufacturers to fly the engine on their own four-engined testbed aircraft. We want to treat our customers as partners in this.”

On CFMI’s ducted fan studies, Snecma civil engines director general Jean-Pierre Cojan told Aviation International News the contrarotating ducted fan is being revisited because today’s three-dimensional aerodynamics design capabilities, coupled with the advanced composite blade technology now being applied to turbofans, might make a ducted contrarotating fan viable.  “There have been huge advances in technology in the 20 years since UDF,” he said.

“This is the most interesting time I have seen in the engine industry in the 27 years I’ve worked in it,” Cojan added. We all know there will have to be a quantum leap in fuel efficiency, maybe 15 percent, before the manufacturers commit to new single-aisle aircraft. There are some very exciting new technologies and some very demanding requirements–not just fuel burn, but noise and emissions as well. We agree with Pratt & Whitney that the GTF offers great specific fuel consumption but we also believe the geared system is too heavy and will create too much waste heat. In the end the efficiency gains will be wiped out.”

P&W is the only one of the powerplant manufacturers to be pursuing the GTF, although it is understood it has a back-up Advanced Turbofan under development in case the GTF runs into problems. CFM International and Rolls-Royce have rejected the geared fan solution out of hand–and so far have publicly committed to improving their conventional turbofan technology to provide the single-aisle powerplant solution.

The different approaches to future single-aisle engines being taken by Pratt & Whitney and Rolls-Royce, its main partner in the International Aero Engines group, remain the subject of “interesting discussions,” according to Douglas Scheffel, P&W’s general manager of commercial engines. “We think we can have a constructive dialogue.”

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