Pratt’s PurePower geared turbofan family takes off

By: Julian Moxon

July 15, 2008
Aircraft

Clouds of dry ice swirled around onlookers as Pratt & Whitney revealed a full-scale model of its new “PurePower” PW1000G geared turbofan (GTF) on its stand yesterday. The engine is performing “outstandingly well” in flight tests now under way, said Pratt & Whitney president Steve Finger, who added, “This is the first of a new generation of ultra high bypass engines.”

Such is the confidence in the program that the company is now talking openly about the GTF concept, until now aimed at the next generation of 150- to 250-seat aircraft, applied as a replacement for its much larger PW4000.  Bob Saia, Pratt & Whitney’s vice president, next generation product family, said talks with “one of the OEMs” about a GTF-based engine for future large widebody aircraft have already taken place. “We’ve been doing studies for a next generation widebody which would enter service in 2020–2025. We’d need to commit to an engine four or five years before that,” he said.

The geared fan concept “is not thrust limited” and the PW1000G will form the basis of all future large aircraft turbofans, said Saia. The 17,000-pound-thrust 1217G engine has already been chosen to power the Mitsubishi MRJ70 and MRJ90 regional jets and the 24,000-pound-thrust PW1524G for the Bombardier C-Series. The PW1217 will go to test late next year, the PW1524 a few months later.

The GTF made its flight aboard the Boeing 747 testbed a few days before the show began. Early results are “extremely promising,” said Saia. “We completed two one-hour flights on the first day of testing and the engine performed flawlessly.” A 40-hour test program is planned, following which the engine will be shipped to Toulouse for 75 hours of flight trials aboard an Airbus A340-600 towards the end of the year.

Both Pratt & Whitney and Airbus deny media speculation linking the A340-600 trials to a possible A320 re-engining opportunity.  “All of our studies are focused on a new aircraft,” said Saia. “For us it is just a trial,” added Stuart Mann, director of product marketing for the A320 family. “It is far too early to speculate on the outcome. There are other engine possibilities we want to consider as well. We’re keeping all our options open.

“The A340 flights will give us a chance to look at the engine installation, the variable area nozzle, gearbox cooling and oil issues,” added Mann. “There are so many questions to be answered before we can decide which way we’re going on this.”

Early indications are that the PW1000G is “amazingly quiet,” said Saia. “We’ve seen noise levels 20dB below Stage 4 in ground testing and we think a future geared architecture engine could do even better.”

The all-new eight-stage high-pressure compressor for the production engine has already built up 250 hours of tests, said Saia. The company is also developing a new high-pressure turbine and combustor, the resulting advanced core featuring “the best technology available.”

The commitment to the geared turbofan concept is now so strong that Pratt & Whitney has essentially abandoned its original idea of a fall-back engine, Saia said. “We’ve done more than 40,000 hours of gearbox rig testing. We are very confident this is the way to go.”

The engine now flying on the Boeing 747 is producing 30,000 pounds of thrust, thrust, although it has been taken repeatedly to the 40,000-pound “red line” in ground test. “We see no limits on thrust here,” Saia said. “This is the best solution for future widebodies as well as for the A320 and Boeing 737 replacement.”  

Volvo Boards Pratt’s GTF

Volvo Aero and Pratt & Whitney have signed an agreement under which Volvo has become one of the OEM’s partners on the geared turbofan program. The Swedish firm will take responsibility for the intermediate case and the turbine exhaust case for the engines slated to power the Mitsubishi Regional Jet and Bombardier C-Series airliners. In both instances, the arrangement involves design, development, production and aftermarket. Volvo will also manufacture low-pressure turbine shafts.  

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