FIGURE 2.1 Artist’s rendering of a possible future subsonic aircraft using boxed-wing configuration to reduce drag and increase fuel efficiency. This is one of many possible configurations for future airliners. SOURCE: NASA/Lockheed Martin; available at http://www.nasa.gov/topics/aeronautics/features/future_airplanes_index.html.
consist of the Protruded Rod Stitched Efficient Unitized Structure (PRSEUS), which will be composed of stitched carbon-epoxy material. Finally, reducing specific fuel consumption will not only help improve fuel efficiency but also suppress noise.
Substantial improvements in fuel efficiency will probably require entirely new aircraft designs that are different from the traditional “tube and wing” design. The ERA project is investigating novel hybrid wing body configurations that integrate airframe and propulsion systems to improve fuel efficiency as well as help meet 2020 noise reduction goals.3 The Boeing/NASA X-48B BWB sub-scale research aircraft is the first step in that process (see Figures 2.2 and 2.3). The X-48B flew its first flight test on July 20, 2007, and recently completed Phase 2 testing.4 The aircraft will resume flight testing in the X-48C configuration, with two turbofan engines instead of three turbojet engines used on the X-48B.
The ERA project’s goals are the N+2 goals, or 2020 technology benefits relative to a large twin-aisle reference configuration, including a 42-dB noise reduction below the stage 4 noise requirements, a 75 percent reduction in landing and takeoff NOx emissions below Committee on Aviation Environmental Protection 6 (CAEP 6) requirements, and a 50 percent reduction in aircraft fuel burn. These final technologies will include airframe technology, propulsion technology, and vehicle systems integration.
In an effort to achieve these goals, the ERA project is investigating 36 different projects, with the goal of reducing them to only 6 in phase 2, which is planned to take place in spring 2012. In the committee’s view, it is important to reduce the projects based on technical merit and not on their expenses to date. NASA had plans to develop a “sub-scale test vehicle” by 2016 to demonstrate a number of the key technologies identified in this
3 NASA Aeronautics Research Mission Directorate, “Fundamental Aeronautics Program: Subsonic Fixed Wing,” available at http://www.aeronautics.nasa.gov/fap/sfw_research_overview_feature.html, last updated September 9, 2009.
4 NASA Dryden Flight Research Center, “Back in the Air: X-48B Resumes Flight Tests at NASA Dryden,” available at http://www.nasa.gov/centers/dryden/status_reports/X-48B_status_09_21_10.html, last updated September 21, 2010.