Monday, June 1, 2009
Pratt & Whitney's John Saabas, Paul Adams and Bob Saia
Aviation Maintenance recently had the opportunity to hear from key executives at engine manufacturer, Pratt & Whitney, including Paul Adams, senior vice president for engineering, Bob Saia, vice president of next generation product family, and John Saabas, president of Pratt & Whitney Canada, about the geared turbofan (GTF) and other subjects.
AM: We’ve heard a lot about the new geared turbofan engine. Are you working on the next-generation GTF?
Adams: The current product we’re demonstrating, which is the basis of the design of the CSeries and the Mitsubishi Regional Jet, is the first step in a long-term evolution. Using the gear technology enables us to build engines that have a much higher bypass ratio than conventional engines... for example, engine bypass ratios from 12 – 13 [for current GTF family] to 18 – 20. This is the performance level we require to get significant improvement, longer term, in terms of fuel burn, noise and maintenance cost. What we’re really trying to do is to increase the engine bypass ratio, reduce the fan pressure ratio and increase the propulsive efficiency.
AM: What about the next-generation narrowbody, specifically?
Saia: We want to develop a bigger engine, in the 30,000-pound-thrust class. So we’ve got a series of features. We’re looking at improvements to the fan, better materials, improved aerodynamics, higher bypass ratio and improved fan drive gear system, while working the core — compressors, combustors and turbines. We want to go to higher gear ratios. Instead of 3-to-1, can we do 4-to-1? A higher gear ratio means we would drive the fan slower and the turbines faster, but probably not change the maximum speed [of the turbines] from where they are today. The whole engine will scale to a larger fan and larger turbine, so maybe we’re talking about 50 to 100 rpm [faster].
AM: How do you reduce nitrogen oxide (NOx) emissions?
Adams: The TALON [Technology for Advanced Low Nitrogen Oxide] combustor uses "rich quench lean" technology. At the point of combustion we have more fuel than oxygen. We want to burn rich and quench the chemical reaction quickly — in microseconds — before nitrous oxide has time to form.
AM: Did Pratt & Whitney Canada also help develop the gear system?
Saabas: We helped with the Advanced Technology Fan Integrator (AFTI) demonstrator in 2000.... The gearbox was designed by us. The AFTI is the predecessor to what they have now. But the gearbox today is a Hartford design.
AM: What do you think of the open rotor concept of the competition?
Adams: The open rotor requires a total redo of everything. Open rotors might be 14 or 15 feet in diameter. They would be mounted on the tail. Because they are so loud and big, you need to get them high enough so they don’t hit the ground and far enough back so passengers don’t get their ears [affected]. We’ve studied open rotors, but our belief is that the ducted configuration is going to be the way the industry goes. One of the big issues is that there’s no certification basis for [open rotors], so FAA [the Federal Aviation Administration] and EASA [the European Aviation Safety Agency] are going to have to write new regulations. They are going to have to ensure that, under all failure cases, they’re safe. How do you prevent a propeller blade from one engine shooting across and hitting either the tail or the opposite-side engine? We don’t know. It’s brand new territory. I think there are concerns about whether you can achieve the same level of safety associated with these configurations and how you would certify them.
AM: On another topic, what’s the status of your CFM56 PMA work?
Adams: We have 19 life-limited parts approved and are bringing them on line in the course of this year. It’s the first time the FAA has given an STC [supplemental type certificate] for life-limited parts... for engine applications. We got all the parts at full up — we did not have to compromise on any of the parts. One of the challenges is that United grounded its 737 fleet and that was a big part of the launch customer set. There’s a list of customers around the world we’re looking at. Jet2.com, a customer we have in Europe — they are putting life-limited parts in the engine now. We have one [customer] in Asia, not disclosed. Interest is high, but what they want us to do is get the parts on the shelf.