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Rolls-Royce moves closer to developing more efficient jet engines
Rolls-Royce has taken a step forward in developing more powerful and efficient jet engines for commercial passenger aircraft with successful tests of a vital component for its UltraFan design.
The company has started tests of a “powered gearbox” linking the turbine at the back of the engine with the giant fan at the front.
Traditionally these parts are directly linked, meaning the speed of the fan, which produces the majority of the thrust of a modern jet engine, is directly controlled by the turbine, which is driven by hot gases being forced out of the back of the engine.
As fans become bigger to generate more power, the turbines at the back have to become larger and heavier so they can drive the fans at the front, with the turbines eventually becoming so large that they eliminate the gains of a bigger fan.
To give an idea of how large fans have become, the Rolls-built engines for Airbus’s latest A350XWB passenger jet are bigger in diameter than Concorde’s fuselage.
Rolls’s UltraFan design gets around the problem of a large fan by using a gearbox between the fan and the turbine. This means the turbine can spin at high speeds, where it is more efficient, while the gearing ensures the fan can turn at the lower speeds where it performs best.
The powered gearbox is designed to handle loads of 100,000hp, the equivalent power output of 1,000 family cars, and is a first for Rolls.
The company hopes the gearbox will allow the fan and turbine each to spin at optimum speed for whatever part of the flight an aircraft is in, be it take-off, cruise, climb or landing, cutting fuel consumption.
The tests that the gearbox is undergoing at Rolls-Royce as the company prepares to run it up to full power place it on a rig which simulates the engine in different positions such as steep climbs and turns, as would be experienced in flight.
Mike Whitehead, Rolls-Royce’s chief engineer on the UltraFan, said: “This is a significant step in bringing our future technology to life.
“We launched the UltraFan design in 2014 and now we are putting our new infrastructure to work to turn it into reality.”
Using gearboxes to produce more efficient jet engines is not a new idea but few companies have been able to successfully implement them.
The American jet engine manufacturer Pratt & Whitney’s geared turbofans have suffered technical issues, causing delays for the small Airbus A320 jets they are being fitted to, and no company has yet delivered a geared turbofan engine for larger jets, the market that Rolls-Royce is focused on with its engines.