Rolls-Royce has revealed Liebherr-Aerospace as the surprise partner with which it plans to develop a power gearbox for its future family of UltraFan engines.

The 50:50 joint venture, announced by the two companies on June 10. will be established in Friedrichshafen, Germany, where Liebherr will make the initial power train gearboxes. Rolls, which will lead the design definition, integration and testing of the power gearbox, says the joint venture “will review the possibility of a standalone manufacturing infrastructure at a later date.”

Rolls revealed in May that it had frozen the design of the first test gear unit for the UltraFan, and has begun machining work on components in parallel with development of an evaluation rig in Dahlewitz, Germany. Rolls-Royce is investing more than 80 million euros (US$90 million) in the expansion of the research site, partly funded by the Brandenburg regional government.

Although General Electric-owned gear provider Avio Aero was not expected to be named as the Rolls partner on UltraFan for competitive reasons, there had been speculation that Aero Gearbox International (AGI), the recently established Hispano-Suiza and Rolls power transmission joint venture, could be given the role. The selection of Liebherr, which builds large, multi-stage planetary gearboxes for wind turbines and has little previous experience of large aero engine transmission systems, is therefore something of a surprise.

Liebherr-Aerospace production, purchasing and asset investments managing director and COO Josef Gropper, says participation in the UltraFan demonstrator effort “gives us the opportunity to break new ground and significantly enlarge our scope of activities."

The UltraFan is aimed at future airliners for 2025 onwards, and will be the first Rolls-Royce large commercial turbofan to incorporate a fan driven by a power gearbox. The company says, however, that it has significant experience producing gear drive systems for the AE2100 and T56 turboprops, the lift fan for the F-35 Joint Strike Fighter, and the Model 250 turboshaft for light helicopters.

Rolls revealed plans in 2014 to adopt a geared turbofan design as part of a two-step evolution of its current three-shaft turbofan architecture to meet future demands for higher propulsive and thermal efficiency.  Similar in baseline concept to Pratt & Whitney’s PW1000G geared turbofan, the UltraFan will be aimed at medium and higher thrust applications anywhere up to the 100,000 pounds-thrust power range.  The engine will have a very large 15:1 bypass ratio and overall pressure ratio of 70:1 which, together with the efficiency of the gear system, is expected to provide a fuel burn improvement at least 25% better than the Trent 700