Aircraft

Pratt & Whitney remains confident its geared turbofan (GTF) development will still become the most attractive option to the next-generation narrowbody designers, despite renewed studies of potentially more fuel efficient, but longer-term open rotor or "propfan" concepts by CFM International and Rolls-Royce.

The company, which is on track to start ground tests of a PW6000-based GTF demonstrator by the end of this year, believes its head start will not only give it pole position in the race to win emerging applications, but will also give it greater opportunities for product improvement. P&W Commercial Engines president Todd Kallman says "this is not just a one-step change. We're going to continue to improve on this in the future."

Even in its planned production standard configuration P&W maintains the fuel burn, emissions and noise benefits will outweigh the complex airframe integration issues posed by the open rotor concepts. P&W plans to flight test the demonstrator in 2008, and have a production-ready GTF version available for service entry as early as 2012-13, whereas the earliest open rotor availability is not expected until 2019-20.

"We believe the GTF provides almost all the benefits of a propfan. It's a couple of per cent different in fuel burn, but the other attributes will more than make up for that in terms of significantly lower noise, and with our improved combustor technology we can work the emissions. It also does not require significant changes to aircraft integration," says Bob Saia, vice-president of commercial engine developments. He adds that the large rotor diameters of the concepts dictate the use of unconventional configurations.

P&W has targeted a 12% fuel consumption reduction for the GTF against current engines such as the V2500 or CFM56, a 40% reduction in maintenance costs, noise levels of around 15dB below Chapter 4 and emissions as much as 70% below the CAEP2 limit. CFM, which revealed new details about both its LEAP56 technology plans, a subset of which involves open rotor concept studies, is aiming for between a 10-15% fuel consumption cut and 10 to 15dB lower noise than current engines with the baseline configuration. The open rotor concept, it says would cut fuel use by around a further 10%, but only at noise levels comparable with those of current engines.

Assembly of the GTF demonstrator meanwhile continues at Middletown, Connecticut with the first parts of the new low-pressure spool and other "GTF unique elements" due to be mounted on the PW6000-based high-pressure core in late June. "By the end of July, right after the Paris air show, we will start to put the low [pressure] turbine module on the assembly," says Saia. The addition of each element, including the Avio-built fan gear drive unit, LP compressor as well as the MTU-developed high-speed LP turbine, will only be completed once rig tests on the relevant piece have been finalised, he adds.