April 22, 2013
Credit: Pratt & Whitney
Pratt & Whitney's promises over the geared turbofan's step change in fuel burn for mainline single-aisle airliners are about to be put to the acid test as the first PW1100G for the Airbus A320NEO is prepared for flight.
The flight tests, due to begin by June on one of Pratt's two Boeing 747SP flying testbeds, will be critical to assessing not only fuel consumption, but also operability and overall performance in advance of flights on the first reengined A320 late next year. The PW1100G is the first of the new-generation mid-thrust turbofans to fly. The competing CFM Leap-1A from the alliance of General Electric and Snecma, is not due to begin ground trials until September, and will start test flights in 2014.
Many of the operators that have ordered the A320NEO—but have yet to choose an engine—will be watching the flight-test results closely. According to data released by Airbus, the two engine makers are virtually neck and neck. The Leap-1A has been selected for almost 630 A320NEOs on firm order, while the PW1100G has been chosen for 590. However, engines for more than 900 further aircraft on firm order have yet to be officially announced.
The mood at Pratt is optimistic as it begins mating the first engine to a strut developed by L-3 Communications for attachment to the 747 at the Mirabel Aerospace Center in Quebec. Confidence stems from favorable results during ground tests that were completed on the first engine at the company's facility here in early April. The engine, rated at 33,000 lb. thrust, accumulated 120 hr. in trials that began in early December and ended with acoustic tests on April 10.
Pratt & Whitney President Dave Hess says performance evaluations to date are positive. “We feel we're on the mark, and meeting the projections we made,” he says. Pratt originally targeted the PW1100G at a 12% better fuel burn on the A320 than the CFM56-5B and now believes it has a 16% advantage. “In the development program, we're where we need to be. In fact, we're right on the mark for delivering on fuel burn on all three of the platforms,” he adds, referring to the geared-turbofan-powered A320NEO as well as the Mitsubishi Regional Jet (MRJ) and Bombardier CSeries.
A second PW1100G engine is undergoing structural trials and is poised for crosswind evaluations. The tests will assess fan characteristics and flutter margin before the engine moves on to other low-pressure system stress tests. The fan blade is a larger version of the same bi-metallic blade developed and tested for the CSeries that has proven highly robust in testing, says Bob Saia, vice president of Pratt's Next-Generation Products Family. “We hit a home run with this new fan blade,” he says.
The blade had greater flutter margin than predicted, which enabled Pratt to discard the variable area fan nozzle (VAFN) from the CSeries's PW1500G engine late last year. The feature dynamically alters exit nozzle area for different phases of flight to maintain blade stability It remains part of the baseline on the Pratt-powered A320NEO and will be certified in this configuration. On larger engines, such as the PW1100G, the VAFN offers the potential for additional fuel savings as well as maintaining flutter margin. For smaller engines, like the PW1500G for the CSeries, the specific aim is to safeguard the fan, and Pratt says fuel efficiency will be better without the feature.