CFM International has committed to developing a new baseline engine for the next generation of narrowbody aircraft under the Leap-X banner while stressing that it will continue to work on open-rotor technologies.

The GE Aviation/Snecma joint venture, which dominates the narrowbody sector, believes it can deliver an engine that will provide 16% lower fuel consumption than today's engines by 2016.

But it also thinks an open-rotor design could provide an equivalent 26% reduction if major challenges related to noise, maintenance costs and aircraft design can be overcome.

Leap-X will feature a radically new fan design providing a 9:1 by-pass ratio, and an advanced core with dramatic aerodynamic and material improvements.

 CFM leap X

Its formal launch provides airframers such as Airbus and Boeing with the prospect of a markedly more efficient engine by 2016 and is likely to increase pressure on them from some cost-burdened airlines for them to commit to new aircraft designs.

But the continuing open-rotor work will also hold out the promise of substantially greater gains if the world can wait for the technical issues to be solved.

"We are committed to the Leap-X schedule for 2016," says CFM executive vice-president Bill Clapper. "We are also committed to running the tests for the open rotor. When we get the open-rotor data we will look at it at that time. Both [Boeing and Airbus] are very active. We are bringing this to them so they can do their design studies."

By 2016 CFM believes that as well as the fuel-burn gains, Leap-X also will provide a 10-15dB margin over stage four noise levels, and 60% lower NOx emissions versus CAEP 6.

In order to keep the weight of the enlarged composite fan acceptable, it will be manufactured using resin transfer moulding techniques for the first time.

Instead of laying up composite laminates, the composite fibres are woven together on a loom and the resin poured around it in a mould before curing. The 180cm (71in) blades will have titanium leading edges.

Using composites in the fan and the case is predicted to save 450kg (1,000lb) per aircraft. A full-scale demonstrator of the fan is due to run in the last quarter of 2008.

The new core features an eight-stage compressor and single-stage turbine benefiting from advanced 3-D aerodynamics, new materials - such as titanium aluminide in the low-pressure turbine, and a reduced blade count. All this is married to CFM's TAPS II combustor. Hardware is already being produced ready for testing in mid-2009.

The open-rotor work builds on the unducted fan flight-test programme of the late 1980s and will incorporate Leap-X technologies where appropriate.

Clapper says: "We believe that all these [Leap-X] technologies apply to open rotor, but there are more technologies required for the open rotorthe carrot is 10% better fuel burn, but you must solve the noise problem."

After noise, he says, the second challenge is the maintenance costs related to the pitch-change mechanism of the blades and the counter-rotating nested turbine. The third challenge is the installation of the engine - which could be 4.3m wide.

Safran Group and General Electric have agreed to form a joint venture that will develop, produce and support engine nacelles and subsystems for the next generation of narrowbody aircraft. Under the new 50:50 joint venture Safran company Aircelle is teaming with GE's fully owned Middle River Aircraft Systems subsidiary. "The next generation of engine nacelles will require new technologies and significant financial resources for their development," says Aircelle chief executive Jean-Pierre Cojan.

Source: Flight International