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Pratt & Whitney argues geared-fan engine design is superior to open-rotor concepts

Pratt & Whitney will seek to establish the geared turbofan (GTF) as a superior alternative to open rotor technology for next-generation narrowbody engines until at least 2020.

The company has outlined a technology growth path from 2013 to 2020 that is intended to break the impression that GTF is a stop-gap solution until the arrival of open-rotor technology later in the decade.

P&W's current development supports an entry into service for the geared powerplant as soon as 2012, assuming a next-generation narrowbody programme, such as the Bombardier CSeries or the Mitsubishi Regional Jet (MRJ), moves forward into full-scale development later this year.

Following entry into service, P&W's technology path offers the potential for inserting two or three upgrade packages over the next eight years aimed at reducing fuel burn or lowering maintenance cost.

Pratt & Whitney believes its geared-fan engine design is superior to rival open-rotor concepts 

"Our technology plans are targeting a 1% a year improvement in specific fuel consumption between 2013 and 2020," P&W says. The insertion packages will focus on introducing lighter materials and advanced materials in the engine's low-pressure turbine.

P&W is pushing forward with GTF in an effort to revitalise its stagnant commercial engine business, with airframers likely to introduce a wave of next-generation narrowbody types from 2012 through the end of the decade.

P&W's new engine will be sized to fit new aircraft types ranging from about 18,000lb thrust (80kN) to 30,000lb thrust, which encompasses the MRJ at the bottom end through the largest of the single-aisle replacements from Airbus and Boeing.

Meanwhile, rivals General Electric/Snecma and Rolls-Royce plan to deploy improved engine cores in the 2012 timeframe and perhaps leap to open-rotor technology after 2015.

But P&W disputes claims that open-rotor technology will offer an improvement over the GTF engine. Although laboratory benchtests indicate an advantage for the open rotor, such benefits will be eroded by trade-offs necessary for installation, said Bob Saia, vice-president of the next-generation product family.

The open-rotor fan diameter may be nearly twice as wide as ducted nacelles, he says. The size of these engines will add weight and require larger struts if mounted on the wing. The airframe may be forced to mount the engines on the body of the fuselage, adding even more structural weight. A wing-mounted open rotor fan also would sharply increase noise, requiring additional insulation inside the airframe.

"We still don't see how we overcome the hurdles of what we're talking about," Saia says. With GTF, he adds, "you can get open-rotor fuel efficiency without sacrificing any noise".

P&W is developing an all new engine for the commercial family of products. Separately, the company is seeking to develop a new engine core derived from the Improved High Performance Turbine Engine Technology programme.

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