PW close to deciding on GTF fan blade material

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Pratt & Whitney says it will decide by the third quarter whether to use traditional hollow titanium fan blades or a newly developed hybrid metallic design for its new geared turbofan (GTF) engine.

"We're leaning toward the hybrid metallic blade," Paul Adams, senior vice president of engineering for the Connecticut-based United Technologies subsidiary, tells ATI and Flightglobal.

Along with P&W's internal work on the hybrid metallic blade, which Adams describes as a "metallic structure associated with a composite structure", the company also investigated with its sister company Hamilton Sundstrand a resin transfer molding (RTM) composite design, similar to what GE uses on the GE90 series engines for widebody aircraft and for its new Leap-X1C narrowbody engine, selected by Comac for the C919.

However, Adams says engineers have ruled out the RTM option in part because the hybrid metallic design is "more efficient" due to its thinner leading edges and other features, including better foreign object debris (FOD) resistance.

To date, Adams says P&W has completed 95% of the development work required to make the blade decision, with the fall-back position being traditional titanium fan blades.

If the company goes forward with a hybrid metallic design, Adams says the blade could be used on other engines as well.

Elsewhere on the GTF, P&W is planning to use titanium blisks for the "front half" of the high pressure compressor of the engine, and nickel construction for the back half.

Adams says the turbine blades will also be made of conventional materials, allowing maintenance shops to service the engines with existing processes and materials.

Selected for three platforms to date, the PW1000G engines are designed to deliver fuel burn savings on the order of 16% compared to the CFM56-5B and 20% lower maintenance costs for the life of the engine.

Core testing for the Bombardier CSeries and Mitsubishi Regional Jet started in December 2009.

P&W plans to start full engine tests in the third or fourth quarter this year, says company president, Dave Hess.

An earlier demonstration engine accumulated 406h of ground and flight testing on a Pratt 747SP and an Airbus A340. The gearing system, which spins the fan at one-third the speed of the low pressure turbine, boosting propulsive efficiency, has been ground tested for 40,000 cycles with no problems or wear, says Hess.

P&W has not yet begun building a prototype core and engine for the Irkut MC-21, its third new aircraft win.