NASA Langley Research Center, in collaboration with Boeing and Lockheed Martin, has developed a new external acoustic liner for aircraft noise reduction. While the acoustic liner can be placed on any external aircraft surface, one attractive application is for open-rotor noise reduction. Airframe manufacturers are considering open rotor engines for future aircraft designs as they provide significant fuel savings. However, open rotor engines have no nacelle and thus, do not allow the use of conventional nacelle liners for noise abatement. This technology strategically places acoustic liners on the external surface of the aircraft to reduce such engine noise.
This technology is an evolution of acoustic liners developed for engine noise abatement that typically are located inside nacelles. The acoustic liners described here can be outfitted on external surfaces and in tight spaces. Three initial areas of the aircraft have been considered as part of an aircraft configuration incorporating an open-rotor propulsion system. The three areas where the liner configurations were applied were under the rotor, on the upper surface of the elevon, and on the surface of a strut.