Machining work on components for Rolls-Royce’s first test gearbox for the UltraFan high-bypass geared turbofan has begun in parallel with development of an evaluation rig in Dahlewitz, Germany, where the company is expanding its research site.

The UltraFan is aimed at future airliners for the 2025 time period and beyond, and will be the first Rolls-Royce large commercial turbofan to incorporate a fan driven by a power gearbox. The U.K.-based engine maker 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 the architecture of the PW1000G geared turbofan family in development by Pratt & Whitney for the lower- and mid-thrust market, the UltraFan will be aimed at medium- and higher-thrust applications up to the 100,000-lb. power range. The core of the engine will be based on the same high- and intermediate-pressure spools to be developed for the preceding three-shaft Advance family. Rolls believes that combining elements of an advanced three-shaft core with a fan drive gear system will provide the best means of achieving efficient designs with a very large 15:1 bypass ratio and overall pressure ratio of 70:1.

“We have now started building the rig facility in Germany and are due to finish by the end of the year,” says Alan Newby, chief engineer at Rolls-Royce aerospace future programs and technology. “It will be early next year by the time we run our first gearbox, though the design of that is frozen. The test rig and the gearbox facility are now being developed in parallel.”  

Progress on construction of the site, which includes a power rig and capacity for a later attitude rig, has been swift thanks in part to the recent mild winter in Germany. The power rig will simulate loading conditions in flight and will be sized to accommodate 15-80-megawatt gear systems. Rolls is recruiting up to 200 gear system engineers for the Dahlewitz site and is seeking expertise in gearbox systems, including all associated components such as spur gears, bevel gears, bearings, drive-shafts as well as housings and casings.

Design details of the gear system and a gearbox development partner selected by Rolls remain confidential.  “We have done a lot of work on the optimum configuration, and we have picked a solution that will deliver,” says Newby. The ratio of the initial test gear “will be approaching 4:1,” he notes. “The first gearbox build we do will allow us to do a lot of trades on what follows.” Three gearbox versions will be built before Rolls mounts one on an engine for flight testing.

Partly funded under the European Clean Sky 2 research program, the UltraFan demonstrator will culminate in a flight-test effort using a donor engine from the earlier Advance development program. The demonstrator unit will include the core engine, power gearbox, high-speed turbine, low-speed fan and integrated, slim-line nacelle. 

This article was originally published on May 26.