General Electric is studying a new growth variant of the CF6-80C engine which will be aimed at the planned 747-400X stretch, as well as increased gross weight variants of the 767-400ER.

The new study variant, known as the CF6-80CG2, will have a baseline thrust capability of 290kN (65,000lb), and could gain the initial go-ahead this year, with a launch in early 1999, says Roger Seager, general manager of the CF6 project.

The G2 design tackles three key target areas required for the growth 747 - acoustics, fuel consumption and thrust, yet allows GE to offer a solution using the same pylon and nacelle as the current CF6 installation. "In that case, Boeing doesn't have to go into a new engine certification, which saves it millions of dollars," says Seager.

A vital part of the G2 is an "innovative" core and fan flow mixing technique, developed through GE's internal research and development efforts. GE declines to give details of the system, but says that the design, which does not require an extended nozzle or casing, will be perfected by the end of the year. Seager adds that it will already "give enough decibel margin" to meet any future noise limits at London Heathrow.

Fuel consumption is being tackled with the extensive application of advanced three-dimensional (3D) aerodynamic modifications to the aft stages of the high pressure (HP) compressor and HP turbine. "By putting 3D aero into the back of the compressor and in the HPT, assuming we will use a boltless turbine [already developed for the -80C2B7F1 and -80C2B8F], it will allow us to run with fewer blades," says Seager. Total engine specific fuel consumption improvement is expected to be as much as 5% in terms of fuel used per seat/km, over the current CF6 models now powering 747-400s.

Thrust is increased largely by use of a hybrid wide chord fan. This combines the aerodynamic benefits of a solid titanium wide chord fan blade with the lighter construction of a hollow unit. The wide chord blade provides potential for higher thrust operation at the existing 2.36m diameter, and offers up to 5% thrust growth beyond 291kN.

Details of the plan were presented to GE chairman Jack Welch on 12 March, as the company reviews its options for future 747 derivatives. To avoid a potential clash with the GP7000, under development with Pratt & Whitney for the Airbus A3XX and stretched 747, GE is expected to target the G2 only at derivatives up to around 426,700kg take off weight. The GP7000 would therefore be offered for the 747-400Y derivative which incorporates a wing root insert and has a take-off weight of over 483,500kg. The G2 would also be offered for higher gross weight versions of the 767-400ER.

Source: Flight International