General Electric has revealed plans to equip the GEnx engine for the Boeing 7E7 with a composite fan case, as well as composite fan blades, representing a significant departure from all previous jet engine designs.

The development will save weight and improve performance, says GE, which pioneered the first large-scale use of composite materials in jet engines with the fan blades for the GE90. By replacing the standard metallic fan case material with composites, the company predicts weight savings per engine of close to 160kg (350lb), or 320kg per shipset. However, further knock-on weight reductions from the lighter installation mean the overall weight saving will be more than 360kg per aircraft, it adds.

The fibre-braided fan case, made from carbonfibre composites, will extend aft from the inlet lip flange to the thrust reverser, which will be conventionally constructed. "There is no drawback to doing this," says GEnx marketing general manager Mike Wilking. "It produces weight savings and superior strength, and you get better containment and half the density. We don't even need a Kevlar wrap for containment, it's so tough." The composite fan case successfully passed a "proof-of-concept" subscale rig test last month, and a further series of evaluations is planned from April 2005 with a larger-scale rig test. Additional full-scale blade and case rig tests are set for late 2005 and early 2006, says Wilking, who says the system will be designed for growth to accommodate power up to and exceeding the up to 75,000lb thrust (334kN) specified by Airbus for the A350. The engine is set to be certificated at 70,000lb for the 7E7 in 2007, with derated versions available at lower ratings down to 55,000lb.

Performance improvements are also expected from the design, which is inherently more rigid than metal, says Wilking. This will mean less distortion under various loading conditions, with less tip losses and higher blade efficiency throughout the envelope, he adds.

"It will stay round, which is good," says Wilking, who adds that the composite case, plus other possible weight-saving features, will be assessed in January, when the design is to be frozen


Source: Flight International