New advances in open rotor engine technology can make airliners more fuel efficient, but still face a noise problem, NASA researchers say.
NASA's Glenn Research Centre in October completed a two-year-long, initial feasibility study of a "modern" open rotor engine.
A full report on the study's findings will be published later this year, but in the meantime NASA has revealed two important results.
The study proved that an open rotor-powered airliner burns 9% less fuel compared to a similar aircraft equipped with geared turbofans, said NASA aeropropulsion analyst William Haller at the 50th Sciences Meeting of the American Institute of Aeronautics and Astronautics.
The same study also showed that there is a large noise penalty for the open rotor, which is 12db louder than the geared turbofan in the same configuration, Haller said.
NASA's study compared two MD-90s with 162 passengers flying 3,250nm at a cruise speed of M0.78. The open rotor engine was mounted in a pusher configuration.
Although NASA has not yet released the full result, the noise difference between the two aircraft could dampen enthusiasm for open rotor engine technology.
General Electric revived the open rotor concept in 2007, saying new advances could allow such a propulsion system to achieve higher fuel efficiency targets without being significantly louder.
NASA launched the study under the subsonic fixed wing research programme. The agency is seeking to identify and develop technologies that could achieve new breakthroughs in quieter and more efficient commercial aircraft that would enter service after 2025.