Farnborough Air Show

Open rotors brushed off by Pratt & Whitney

 - July 19, 2010, 11:31 AM

Pratt & Whitney believes open rotors are not the solution to powering future single-aisle aircraft and will offer developed versions of its PW1000G series of geared turbofans for all new and derivative single-aisle aircraft.

“We believe we can get better fuel efficiency than open rotors with our engine by leveraging the technology we already have,” said Bob Saia, vice president, P&W next-generation product family. He added that in its most developed form the geared fan engine could bring 30- to 35-percent reduction in fuel burn over today’s engines. “That’s better than an open rotor and it has none of the noise and installation negatives.

“We are positioning ourselves for all potential applications, whether new or re-engined,” said Saia. “We never really embraced the open rotor because when we tested one on the MD-80 in the late 1980s we found there were serious noise and installation problems. With a geared engine we keep the nacelle, and the fan turns more slowly. It’s simple physics.”

Testing to date has increased confidence in the PW1000 gearbox to the extent that P&W will be able to increase the reduction gear ratio of the fan drive system from today’s 3:1 to 5:1. “This means the relationship between the fan and turbine will be even better,” said Saia. “Coupled with other improvements, we can achieve another 10- to 15-percent reduction in fuel burn over the engine we’re testing today. That puts us in the same arena as the open rotor.”

Currently, the PW1000 has found three applications: the Bombardier C Series and Mitsubishi MRJ regional jets, and the 140- to 220-seat single-aisle Irkut MC-21 airliner. The first engine for the C Series, the PW1500G, is to go to test in August, with certification and first flight in 2012. Testing of the MRJ engine is to begin at the end of the year, aiming for a 2014 in-service date, while the more powerful MC-21 engine, producing up to 35,000 pounds thrust, is expected to be certified in 2014 and ready for service entry two years later. “By the time the MC-21 enters service,” said Saia, “around 400 PW1000s will be in service and will have accumulated a million hours of revenue service.”

Hopes remain high at P&W that Airbus and Boeing will offer the PW1000 engine for re-engined versions of the A320 and Boeing 737. Assuming the geared fan meets performance claims, P&W would then be well positioned to power an eventual all-new aircraft, effectively leaving its International Aero Engines partner Rolls-Royce out of the single-aisle market for the foreseeable future.

Saia said P&W is “still talking” to its International Aero Engines partners about joining the PW1000 program. One of them, Germany’s MTU, is already involved in the low-pressure turbine, but despite Saia’s assurance to AIN that “there’s always a way of making partnerships work,” Rolls-Royce has made it quite clear it disagrees totally with the geared fan concept. Like CFM, which is developing its Leap-X, it has conventionally configured advanced turbofans under development for the 150- to 220-seat market. The UK company has said its Advance2 program could lead to an engine in 2016-2017. This is too late, however, for the 2015 date being touted for a re-engined A320.

Initial versions of the PW1000 will be capable of up to 40,000 pounds thrust, Saia said. P&W remains committed to continuing development of the geared engine for widebody applications as well. “We see no reason not to go to 100,000 and beyond,” he said. “It’s our next area of development.”