Bear with me on this one as there is a military point to this post, eventually. I covered the AIAA aerosciences meeting in Orlando in the first week of January, at which there was a day-long session on what NASA calls hybrid wing-bodies, but we all know as the blended wing-body, or BWB. A troupe of folks from NASA and Boeing briefed the audience on progress with flight testing of the X-48B and research under way into improved BWB, sorry hybrid wing-body, designs.
One of these is called the N2A, and is a low-noise configuration that incorporates some changes from the "classical" BWB design represented by the X-48B. These include moving the vertical surfaces inwards from the wingtips to provide shielding of the jet noise. The engines are moved forward for the same reason. Aeroacoustic windtunnel testing of this design is planned for 2011, and Boeing is looking at modifying the X-48B in a similar way to flight test a low-noise BWB.
Interestingly the Air Force Research Laboratory is co-funding a lot of this work because it is interested in the BWB, sorry hybrid wing-body, as a future energy-efficient tanker/transport. Boeing is trying to persuade AFRL, as well as NASA, to fund a manned flight demonstrator. The design team within Boeing's Phantom Works is coy about its concept for a demonstrator, not least because the Commercial Airplanes folks in Seattle get annoyed every time the BWB attracts attention. But it appears they are looking at a 80,000lb empty-weight, 737-sized cargo aircraft that could be built as a demonstrator and evolved into an operational vehicle.
The BWB folks feel a large-scale manned demonstrator is needed to prove the transonic performance - the subscale X-48B being focused on low-speed flying qualities - and to get real costs and weights for the advanced composite structure, which Boeing calls PRSEUS. Quite who - military or commercial - might be interested in an aircraft of that size and capability is not clear, but with the U.S. Army saying the Air Force is coming round to its vertical way of thinking for Joint Future Theater Lift (JFTL), maybe the need for a fuel-efficient airlifter will take precedence over a super-STOL tactical transport.
* PS - The sharp-eyed among you may notice that the N2A is based not on Boeing's BWB-450-1L design like the X-48B, but on the SAX-40 concept developed by the MIT-Cambridge Institute's Silent Aircraft Initiative. That's so the data generated under NASA funding will be non-proprietary.