Pratt & Whitney Geared Turbofan Promises New Engine Dominance

 - June 13, 2013, 10:50 AM
The PW1500G, due to fly on the Bombardier CSeries this year, saw 4,000 hours of testing before gaining Transport Canada certification in February.

Pratt & Whitney CEO David Hess doesn’t spend time lamenting his company’s decision to forgo a bid for a place on Boeing’s proposed 777X. In fact, during a recent interview with AIN at his company’s campus in West Palm Beach, Florida, Hess expressed not an inkling of regret, evidently taking comfort in the narrowbody market’s virtually unequivocal acceptance of his company’s geared turbofan platform. “Our plate’s pretty full right now,” said Hess. “We’ve got five new development programs and we want to make sure that we execute them perfectly and don’t overstretch ourselves right now.”

Hess said he sees a few years of “tough sledding” as the company launches production and eventually enacts rate hikes, while it waits until the end of the decade to reap any returns from aftermarket activity. Happily for the CEO, the company (Chalet A330) appears to have built a solid foundation on which to reap those rewards.

Having won positions on the Bombardier CSeries, Mitsubishi MRJ, Airbus A320neo, Irkut MC-21 and, most recently, Embraer’s planned second generation of E-Jets, the PurePower geared turbofan (GTF) family has completely revived a company that a decade ago became better known for the well-documented missteps associated with the PW6000 than an organization steeped in any history of producing “dependable engines,” as it was.

Although at the time Hess served as CEO of fellow United Technologies subsidiary Hamilton Sundstrand, he could see as well as anyone the depths to which the company’s commercial aircraft engine business had sunk. “It was a train wreck quite honestly,” Hess said. “But it was also a significant emotional event for Pratt and a great learning experience.”

Hess explained that the experience moved the company to completely revamp its engineering “process” to ensure a level of technological readiness in the geared turbofan not seen in the case of the PW6000, for example. “They established a very rigorous process for developing and introducing innovation and new technology,” he said. “And they’ve stuck to that discipline and that rigor over the last ten years, as they’ve brought forward that technology.”

The transformation started with a commitment to “up-front” investment in the now 20-year-old concept that became known as the geared turbofan. In all, the company has spent some $1 billion on research and development but, perhaps more significantly, “hundreds of millions of dollars” in the five years leading up to the demonstrator’s first flight on an Airbus A340 testbed in 2008.

“So we changed the engineering process and in some cases we changed people,” explained Hess. “And we invested more money earlier in the program than we had done historically, rather than do it once the development program is launched…We developed the technology first, offered it to the marketplace, and then did product development. So it really was a fundamental change in the process.”

Bob Saia, a long-time Pratt & Whitney executive and next-generation product family vice-president, could attest to the change as much as anyone. Saia explained that not only has Pratt returned to ensuring thorough product maturity before launch, it has adopted more robust engineering discipline in terms of evaluating risk and design readiness. In around 2003-2004 it implemented what Saia called a “gated-process model” that ensures it doesn’t reach for too much technology too early in a program’s development.

Pratt & Whitney now uses nine technology readiness levels–a system pioneered by NASA–through which a program must pass before reaching maturity. “[Technology readiness level] one is a gleam in an engineer’s eye, [and it goes] up to nine, being ‘we have done this on multiple programs, multiple products, it’s an industry standard,’” said Saia. “Technology readiness level six is what the industry has defined as the level required to say you understand the technology [and] you understand the technology in the environment it’s going to be used, in the product that you’re developing,” he continued. “So a key criteria we have taken is before we start detailed design on a product [we] have all technologies to TRL-six.”

In the case of the GTF, the program reached TRL 4–the phase in which engineers perform validations at the part level–in early 2007. It arrived at TRL 5–the phase in which whole subsystems, such as a gearbox, undergo testing in a laboratory–in the third quarter of 2007. The program reached TRL 6–the point at which subsystems undergo testing in an engine at the operating characteristics they will encounter in service–when Pratt ran the fan-drive gear system on a 747SP in July 2008.

The company detailed the engine that is due to fly on the CSeries (by the middle of this year) in September 2010. That engine, designated the PW1500G, saw 4,000 hours of testing before gaining Transport Canada certification in February. Next year, Pratt expects to certify what Saia described as the PW1500G’s little sister, the Mitsubishi MRJ’s PW1200G. After running four PW1200Gs for about 1,600 hours by December 2012, Pratt began incorporating certification test “learnings” from the CSeries engine, while Mitsubishi caught up with development of the delayed MRJ airframe.

Pratt expects to start certification testing with the fifth PW1200G at the start of this year’s third quarter, in time for expected regulatory approval roughly a year later. Meanwhile, the engine designed for the A320neo, although significantly larger and built with a different core, will also benefit from Pratt’s experience with the PW1500G. Saia recounted a problem encountered during testing of the CSeries engine involving a seal meant to prevent hot gas from raising the temperature within an oil cavity. Of course, engineers changed the seal design and adopted it in the other engines.

Now deep into testing of the neo’s PW1100G, Pratt has built four examples of that variant and, according to Saia, all remains on course for scheduled certification in the third quarter of next year.

The first engine–a performance test article–had accumulated some 125 hours on a stand in West Palm Beach, Florida, before it went to Mirabel, Canada, in late April for installation on one of Pratt & Whitney Canada’s pair of Boeing 747SP test beds. There, it is undergoing flight trials while the second engine continues fan and low-pressure compressor and turbine tests. The third engine undertook icing tests in Thompson, Manitoba, in April, before embarking on endurance trials. The fourth engine, designated to perform combustor and high-pressure compressor and turbine testing, was due to begin running last month [May]. Pratt plans to use eight test articles in all, and dedicate the fifth through eighth to what Saia called “detailed certification tests.”

Using a single engine core and architecture for the entire neo family, Pratt & Whitney “optimized” the basic PW1100G for a thrust range between 27,000 pounds for the A320 and 33,000 pounds for the A321, Saia explained. Although the company plans to de-rate the engine for the A319, all will offer virtually the same 16-percent fuel burn improvement and at least 20 percent operating cost benefits over existing-generation engines.