July 01, 2013
Credit: PRATT & WHITNEY
Engine manufacturers constantly trade claims over whose product performs best, traditionally comparing apples to apples, turbofan to turbofan. But as the battle to power the Airbus A320NEO intensifies, engine makers increasingly are exchanging fire over their technology choices. Pratt & Whitney's success in winning five applications for its geared turbofan (GTF)—and defeating conventional turbofan offerings on four of them—has changed the tone of the engine war of words. No more apples to apples, it's now architecture against architecture.
General Electric and Snecma, its partner in the CFM International joint venture, have placed their bets on carbon-fiber and ceramic-matrix composites and other advanced technologies enabling conventional turbofans to continue providing the fuel-burn improvements airlines need. Pratt has put its money on introducing a gearbox to provide a step change in fuel burn and enable the engine to run cooler, with fewer parts and more conservative technology. Now, with one engine certificated and two more on test, Pratt is looking to the future, and its plans could pose a challenge to the other manufacturers.
The skirmishes have implications beyond the horizon of narrowbodies now in development, principally the A320NEO and Boeing 737 MAX, as technology decisions taken a decade ago and now reaching fruition look set to shape commercial engine development for the decade to come. Firmly established in the 15,000-33,000-lb.-thrust range for single-aisle aircraft, Pratt is now eyeing the 70,000-100,000-lb.-thrust requirements for the twin-aisle market dominated by GE and Rolls-Royce.
At the same time, airframers and airlines are demanding ever greater reliability at entry into service, forcing engine manufacturers to select technologies earlier and spend more time and money maturing them even before beginning development of a specific powerplant. The bets each company placed on architectures and technologies a decade or more ago are at the core of today's hype and counter-hype.
CFM International kicked off the latest fracas at the Paris air show, claiming its Leap-1A engine has up to 3% lower specific fuel consumption (sfc) than the rival PW1100G geared turbofan on the A320NEO. “The Leap will go into revenue service on the A320NEO 1% better than the competition, based on testing to date,” says Chaker Chahrour, CFM executive vice president. “It will retain that 1% better than the competition, which when you integrate over time adds up to another 1%. And on the A321NEO, because of the longer legs and our better cruise sfc bucket, we get another 1%.”
CFM's claims are based on results from the latest tests of key advanced technologies in the Leap-1, including 3-D woven composite fan blades, compressor variable bleed valves, and an uncooled ceramic matrix composite (CMC) turbine shroud. Just-completed tests of the third eCore demonstrator—comprising the high-pressure compressor, combustor and high-pressure turbine of the Leap-1—showed “better component efficiencies than expected,” Chahrour says.
Pratt was quick to dismiss CFM's claims, but was stung into defending the technology in its engine and detailing its plans to introduce new advances over time to continue driving down fuel burn. At Paris, President David Hess restated that there is no way CFM can achieve the advantages in fuel burn and maintenance cost it is claiming “unless they defy the laws of physics.” Pointing out the Leap-1A will not run until this fall, he says “our NEO engine is flying and, in the most recent configuration, the fuel-burn numbers are half a percent better than prediction.”