Rolls-Royce has revealed further details of the turbofan it is proposing to power Boeing's 777X concept, indicating that the engine's composite fan could feature as few as 18 blades.
The UK manufacturer's latest production engine - the Trent XWB for the Airbus A350 widebody twin - has a titanium fan equipped with 22 blades.
"Blades are reducing in number, and getting bigger and wider," says R-R vice-president of strategic marketing Robert Nuttall.
Known internally as the RB3025, the engine boasts a fan diameter of 337cm (132.5in), compared with the Trent XWB's 300cm. The dimensions of the RB3025 are "basically governed by installation and transportation issues", says Nuttall, although he adds: "Actually this is the optimum fan diameter at this technology standard. It's a big engine, bigger than we've ever done before."
The 100,000lb (445kN) thrust class design delivers a bypass ratio of 12:1, requiring an overall pressure ratio of 62:1.
"That's a very high pressure ratio," says Nuttall. "This is really quite an aggressive engine, but it's got to be because the target here is to reduce fuel consumption by at least 10%, compared with the existing [GE90-115B] engine on the 777."
The large fan would create some challenges in terms of transporting spare engines, as even with the fan case and core modules separated the only cargo airliner capable of accommodating it would be the 777 Freighter, as the 747F does not have a large enough door.
Boeing last year issued a request for information to rival manufacturers GE Aviation and Pratt & Whitney, as well as R-R, as part of its studies of a replacement for the 777 family - likely to feature a composite wing and aimed at service-entry by the end of the decade. The aircraft is intended to reinforce the manufacturer's competitive position against the A350-1000, the largest member of the under-development twinjet family.
GE, which has an exclusive deal with Boeing to power the 777-200LR and -300ER with its GE90-115B, is offering the GE9X for the 777X, while P&W is studying a geared-turbofan solution. The US airframer could look to launch the 777X as early as the end of this year.