Story ID: 029Nov17
Safran Inaugurates Open-rotor Test Program
By: Guillaume Lecompte-Boinet
Caption: Unshrouded engine technology could save up to 15 percent in fuel consumption.
Word Count: 495
French group Safran is ground-testing its first open-rotor engine demonstrator. The company expects the new unshrouded engine to burn15 percent less fuel than the new Leap series of turbofans, built by the CFM joint venture between Safran and GE.

Safran built an open-air test stand at its facility in Istres, in the south of France, and has been running the open-rotor demonstrator since May. Developed within the framework of the European Clean Sky 2 research program, the open-rotor study carries a funding budget of €65 million ($77 million) over eight years. Tests will continue until the end of the year to validate the demonstrator. "We will have all the technology on the shelf, available to aircraft manufacturers," said Safran CEO Philippe Petitcolin.

The primary target market for the open-rotor concept, at least initially, is single-aisle airliners, the heart of the CFM customer base. Safran has conducted development research independent of open-rotor studies by GE. The partners will coordinate under CFM in the event they launch an open-rotor program. An open-rotor engine would not be certified before 2030, according to Safran.

The breakthrough for the open rotor is a significant boost in bypass ratio, to 30:1 from 11:1 on the Leap. The absence of a nacelle allows for larger fans, thus the increase in bypass ratio. The higher the bypass ratio, the better the energy efficiency of the engine.

The disadvantage lies with the need to completely reconfigure the aircraft. An open-rotor engine cannot be mounted on a wing, but must attach to the rear of the fuselage. The demonstrator has two contra-rotating fans, the blades of which consist of 3D woven carbon composite, like those of the Leap. GE subsidiary Avio of Italy manufactured the gearbox.

Wind-tunnel tests in 2013 helped solve the noise challenge, one of the main hurdles in open-rotor development. "Our demonstrator has the same sound levels as a Leap, thanks to the aerodynamics of the fan blades," explained Safran research and technology director Stéphane Cueille. The company has not scheduled flight-testing.

Airbus, a partner of Safran in Clean Sky 2, has expressed a preference for a more conventional engine architecture known as the Ultra High Bypass Ratio (UHBR) engine, which is encased in a nacelle but offers a bypass ratio of 15:1. The UHBR would burn between 5 and 10 percent less fuel than the Leap, according to Safran. The UHBR, which could enter service by 2025, also does not require much adaptation of the aircraft configuration. "Everything depends on the choice of the aircraft manufacturers," said Petitcolin. "Either they want an evolution of the current single-aisle by 2025-2027, and the UHBR will be possible, or they want a new design beyond a more distant horizon. And that would allow open rotor.”

Safran is working in parallel with GE on the UHBR, but on different technological building blocks. It expects to test the first UHBR demonstrator in Istres at some point beyond 2020.

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