Aircraft

General Electric has opted to slip the final design freeze milestone for the GEnx engine on the newly launched Boeing 747-8 until mid-2006 to take advantage of lessons learned from the on-going development of the preceding GEnx variants for the Airbus A350 and Boeing 787.

The delay of seven months to the freeze decision, or “Tollgate 6”, also helps GE “pace the programmes”, says GEnx general manager Tom Brisken. “We don’t really want to do Tollgate 6 until we absolutely have to,” he says.

“We can have both of the other engines running before that, so we want to know as much as possible before we make that final definition,” Brisken adds. GE held the first 747-8 GEnx design review in the first week of May 2005 and originally planned to hold the “Tollgate 6” design decision in December 2005.

“However, we’ve decided to delay it a little because we have a bit more time,” says Brisken who adds certification is set for 2008 with 747-8 entry into service targeted for 2009.

The engine was chosen by Boeing over the competing Rolls-Royce Trent 1000 in April and differs from the slightly more powerful version in development for the 787 in having a smaller-diameter fan, and new low-pressure (LP) turbine and compressor. Fan diameter will be 2.64m (104in) versus the 2.82m fan of the 787 version, and the engine is adapted to produce bleed air.

Other than the bleed ducts, the core will be identical to the 787 GEnx. The new LP turbine will have six stages, one fewer than the 787 version, while the LP compressor will also be cut by one stage to three. The engine will be rated at 66,500lb thrust, against the higher 75,000lb thrust (296kN) capability of the 787 engine variant.

The “number one” milestone pacing the entire GEnx programme is the first engine to test for the 787, targeted for March 2006. Build-up for the first engine officially began on 18 November.

GE plans to make first test runs of the new 747 engine in the third quarter of 2007, against the former target date of February 2007. Target entry-into-service for the 747-8 is now thought to be August 2009, four months later than the original target.

GUY NORRIS/LOS ANGELES