Rolls-Royce UltraFan Gear Sets New Power Record

Rolls Royce
Credit: Rolls-Royce

Rolls-Royce says the gearbox assembly in development for the heart of the company’s new high-bypass demonstrator engine has set a record-breaking level of power transmission during pre-installation check-out tests.

Developed in partnership with Liebherr-Aerospace through the Aerospace Transmission Technologies joint venture, the power gearbox (PGB) transmitted 64 megawatts—or the equivalent of 85,800 hp.—during tests at Rolls’ dedicated facility in Dahlewitz, Germany. The power level is “a massive tick in the box to say its ready to support the engine demonstrator program,” said Andy Geer, Rolls’ chief engineer for UltraFan product development and technology.

The PGB transfers power from the fast-spinning intermediate-pressure turbine to drive the slower turning fan, allowing both to operate at their optimum speeds, and is key to meeting the enhanced propulsive efficiency targets of the UltraFan. The new engine will be the first large Rolls turbofan to incorporate a power gearbox and represents the first fundamental change to the company’s direct-drive three-shaft architecture since the RB211 was designed in the 1960s.

The UltraFan gear, which achieved 70,000 hp. in tests in September 2017, is a planetary-style gearbox with a ring gear on the outside and five planet gears inside, rotating around a central sun gear. The design drives the fan from a centrally mounted planet carrier unlike the star-style gear system used in Pratt & Whitney’s geared turbofan.

“The PGB operation extended beyond the sea-level maximum takeoff power levels that would be associated with a product of around 80,000-lb.-thrust capability in order to cover the needs of the upcoming UltraFan demo sea-level engine test regime,” said Geer. “This will take test engines beyond service-representative thrust levels to fully explore capability. So far, the PGB has operated to conditions about 10% beyond a service maximum takeoff thrust condition,” he explained. 

For the high-power test, Rolls engineers ran the unit until it was fully thermally stabilized—a test which typically takes around 10 min. to reach the target condition. 

“One of the other things we’ve done with the power gearbox is a demonstration flight cycle in which we simulated a flight from London to New York. This was representative of a flight cycle including takeoff, climb, cruise and descent and all the operating conditions of that cycle,” Geer said.The gearbox for the first demonstrator, UF001,  is set to begin a final pass-off test in Germany in early September before being shipped to the UK for integration into the engine. “The size of the thing is impressive. The power gearbox module with its surrounding engine structure is about the same size as a Tay engine, so it’s a big brute. We are desperately keen to get the unit over and built into the engine now,” Geer added. 

Guy Norris

Guy is a Senior Editor for Aviation Week, covering technology and propulsion. He is based in Colorado Springs.


1 Comment
Would be interesting to compare power density of the Rolls GB vs. PW vs. typical automotive transmission.