GRAHAM WARWICK / WASHINGTON DC
Manufacturers competing to power Boeing's planned 7E7 airliner are looking at the feasibility of development versions of the engine with and without compressor bleed air.
Boeing wants a bleedless engine for the more-electric 7E7, while Airbus would like a version with bleed air for the A330 and Boeing itself is looking at the engine for future derivatives of the 747 and 767.
"Customers would like us to develop an engine that can be used to upgrade Boeing products," says March Young, Pratt & Whitney general manager, commercial engine marketing. P&W is the only one of the "big three" engine makers offering a clean sheet design, dubbed the PW-EXX, for the 7E7. "We are evaluating the differences between bleeded and bleedless. It's too early to say what they will be," he says.
Boeing plans to use an electric environmental control system (ECS) on the 7E7, along with hybrid hydraulic and electric flight controls and other more-electric systems. Power will be provided by enlarged generators on the engine gearbox. Shaft-integrated, or embedded, generators are considered not to be mature enough.
"The engine will be bleedless except for cowl ice," says Mike Benzakein, GE Aircraft Engines manager of advanced engineering. General Electric is proposing a scaled-down, 60,000-70,000lb-thrust (270-310kÑ) version of its GE90. "We can design bleeded and bleedless, but they are not exactly the same engine. A new compressor casing is a minimum, and probably some internal airflow changes," he says.
Boeing is keen to have a bleedless engine as it will make it more difficult for Airbus to respond to the 7E7 by using the same engines to upgrade the A330. But the company says it would like to use the more efficient engines on the 747, and possibly the 767, and does not believe it is practical to modify existing aircraft to an electric ECS.
"Bleedless is not really a performance issue," says Charles Cuddington, Rolls-Royce managing director - airlines. R-R is proposing a scaled derivative of the Trent 900 under development for the A380.
Source: Flight International
