Fuel prices drive new look at open rotor jet engines

'Open rotor' jet engines are back on the agenda. GE Aviation and NASA are teaming on a wind-tunnel test programme to evaluate counter-rotating fan-blade systems for new engine designs that could sharply reduce fuel consumption.

The testing will begin in wind tunnel facilities at NASA's Glenn Research Centre in early 2009 and continue into mid-year. This is not a full engine test, but a component rig test to evaluate subscale fan systems using GE's and NASA's advanced computational tools and data acquisition systems.

Rising fuel prices have led the partners to re-visit open-rotor engine systems. In the 1980s, GE ground-tested and flew an open-rotor jet engine that demonstrated fuel savings of more than 30 per cent compared to similar-sized conventional jet engines Subsequent advances in data acquisition systems and computational tools will enable GE to better understand and improve open-rotor systems.

"GE and NASA journeyed down this path 25 years ago with great technical success," said David Joyce, president of GE Aviation. "Today's fuel crisis greatly influences future jet engine concepts. GE and NASA will evaluate open-rotor concepts in the wind tunnel with far greater technology capability."

For the NASA tests, GE will run two rows of counter-rotating fan blades at 1/5 subscale in several configurations, tested in simulated flight conditions created in Glenn Research Centre's low-speed and high-speed wind tunnels.

GE and the Fundamental Aeronautics Program of NASA's Aeronautics Research Mission Directorate in Washington are jointly funding the programme. Snecma of France, GE's longtime partner in CFM International, will participate with fan blade designs.

Open-rotor jet engine designs are among the longer-term technologies being evaluated for LEAP-X, CFM International's technology programme focusing on future advances for next-generation CFM56 engines.

NASA and GE jointly tested scale-model, counter-rotating fan systems in the 1980s, leading to the development of the GE36 jet engine.

The GE36, which flew on Boeing 727 and MD-80 aircraft, featured an aft-mounted, open-rotor fan system with two rows of counter-rotating composite fan blades. The enormous efficiency from bypass air created by this fan system drove the GE36's dramatic fuel savings. As fuel prices fell sharply in the late 1980s and early 1990s, the GE36 was never launched commercially, though it was recognised as a technology breakthrough.

The upcoming rig tests will focus mostly on the acoustic characteristics of various fan configurations, as well as performance and efficiency characteristics. Engine noise is a prime challenge in operating open-rotor engine systems in a commercial aviation environment.

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