Open-rotor engine may fly this decade

Developers say engine is expected to cut fuel consumption by 30% compared with current aircraft

There are no technological barriers to a contra-rotating, open-rotor aircraft concept engine progressing to flight test, the Clean Sky consortium developing the concept has said.

The engine could replace the turbofan, and features uncased blades positioned on two stages that rotate in opposite directions. Clean Sky said the engine is expected to cut fuel consumption by 30% compared with current aircraft. 

Eric Dautriat, chief executive of Clean Sky, said: “All the potential showstoppers have been satisfactorily addressed and the decision was made to go on with development to go to a flight test.” 

The milestone comes after Airbus completed a technical review of the potential challenges of developing the open-rotor concept. This included looking at the acoustics, performance, weight and potential certification regulations.

Noise levels have previously hampered attempts to develop an open-rotor engine. The open design means that there is no fan case to muffle the sound of the rotating blades. But the Clean Sky project believes that by changing the shape and configuration of the rotor blades, noise could be brought down to levels that comply with regulations.

Engineers spent two years cutting noise levels by looking at the optimum distance between the two contra-rotating stages, the number of blades on each stage and the profile of the blades themselves. Shifting the position of the engines from the wing to the rear of the fuselage also cuts noise, said Dautriat. Safety issues with the uncased propeller blades have been addressed, he said. Ground tests of the engine will begin in early 2016, with flight tests to follow in 2019. Clean Sky said the engine is suited to short- and medium-range aircraft.

Rolls-Royce, Safran and Airbus are involved in the project. They are developing the technology to increase the airflow passing through the fan stage of the engine to boost fuel efficiency. Until now this has been possible by increasing the diameter of the fan, but diameters have almost reached their limit. 

Dautriat said: “We can go further with existing architectures but the open-rotor is more far-reaching. It is the natural evolution of the turbofan.”

The open-rotor engine has been discussed since the 1980s.