GEnx beats rival Trent 1000 to power stretch as US airframer targets mid-year launch
General Electric plans to hold this week the first design review for the GEnx engine variant selected for the Boeing 747 Advanced, and hopes to reach the "Tollgate 6" or final design freeze milestone in December.
The engine was chosen by Boeing over the competing Rolls-Royce Trent 1000 on 22 April and differs from the slightly more powerful version in development for the 787 in having a smaller diameter fan, and new low-pressure turbine (LPT) and compressor changes. "It is very much a design that was made to fit in a close-knit box of specific fuel consumption, fan size and the drag impact of a larger diameter engine below the wing," says GEnx general manager Tom Brisken.
The fan diameter will be 2.64m (104in) against a 2.82m fan for the 787 version. As a result, the overall bypass ratio will be 8.4 compared with around 10 for the 787 GEnx, 8.7 for the GE90-94B and 7.8 for the GE90-115B – the latter pair on the 777. The engine will be adapted to produce bleed air, but "as this core comes straight from the -94B we know how to run this engine with bleed", says Brisken.
Specific fuel consumption was a critical part of the evaluation, says Brisken, referencing the non-stop Hong Kong-New York mission with 450 passengers and a full load. "That's quite a daunting task, particularly that last 200nm [370km]," he says. Other than the bleed pipes, the core will be identical to the 787 GEnx. The engine will also use the same composite materials for the fan case and blades, with scaled differences. The new LPT will have six stages, one fewer than the 787 version, while the low-pressure compressor will also be cut by one stage down to three. The engine will be rated at 67,000lb thrust (298kN), against the 75,000lb thrust capability of the 787 engine variant.
Assuming a Boeing go-ahead of the 747 Advanced programme, which is expected around June or July, GE plans to make the first test runs of the engine around February 2007, with evaluations on the company's 747 flying testbed in the third-quarter of that year, and type certification in April 2008.
GUY NORRIS/LOS ANGELES
Source: Flight International
