GENERAL ELECTRIC is "working with Boeing and customers" on the possible development of a 467kN (105,000lb)-thrust GE90 which could be derated to suit the growing weight requirements of the stretch Boeing 777.

Latest estimates put the projected aircraft's gross take-off weight at around 300,000kg, although this could reach almost 311,000kg, according to some sources. Both Pratt & Whitney and Rolls Royce have revealed plans to meet the growth. P&W has launched a 436kN derivative of its PW4000, called the PW4098.

"We think that as thrust continues to grow, the weight is not going to stay there for long. We'd rather go to a higher thrust and de-rate at entry-into-service to meet the requirements, although nothing is cast in concrete," says GE90 marketing development manager, Vince DiGiovanni.

To achieve the higher thrust, GE is considering "de-staging" the core to give a power range of between 467kN and 480kN. While the engine would retain the existing fan, low-pressure system and casing, the core would differ with the removal of ", or possibly two, stages of the high-pressure compressor. If we launched a programme like this, it would take around 42 months to certify, or something of that order of magnitude," says DiGiovanni.

GE's more immediate plans for the engine cater for potential thrust requirements up to almost 423kN. A modified GE90 will be tested in the first quarter of 1996. The turbofan will form the basis for its bid to power heavier B- market versions of the Boeing 777 now being discussed.

The initial B-market 410kN GE90 will be certificated in May 1996 and enter service on the first aircraft for British Airways in December 1996, de-rated to 400kN. GE says, that the 410kN engine development "gives a cushion" enabling an easy throttle-push transition to almost 423kN.

DiGiovanni says that more than 80% of the certification tests already completed for the 377kN GE90 cover the planned power range. "The blade-off test is valid up to 423kN, for example." The higher thrust is being achieved by using the higher-temperature-resistant Rene material used in the CF6-80C2 in the first two low-pressure-turbine stages of the GE90. Additionally, the first stage of the high-pressure turbine (HPT) will be made from a higher-temperature-resistant advanced mono-crystal material. Bleed air from the core will also be increased to boost HPT cooling levels.

Source: Flight International