A blended wing body, Blended body or Hybrid Wing Body is a fixed-wing aircraft having no clear dividing line between the wings and the main body of the craft. The aircraft has distinct wing and body structures, which are smoothly blended together with no clear dividing line. This contrasts with a flying wing, which has no distinct fuselage. A BWB design may or may not be tailless. The main advantage of the BWB is to reduce wetted area and the accompanying form drag associated with a conventional wing-body junction. It may also be given a wide airfoil-shaped body, allowing the entire craft to generate lift and thus reducing the size and drag of the wings. The BWB configuration is used for both aircraft and underwater gliders.
History
In the early 1920s Nicolas Woyevodsky developed a theory of the BWB and, following wind tunnel tests the Westland Dreadnought was built. It stalled on its first flight in 1924, severely injuring the pilot, and the project was cancelled. The idea was proposed again in the early 1940s for a Miles M.26 airliner project and the Miles M.30 "X Minor" research prototype was built to investigate it. The McDonnell XP-67 prototype interceptor also flew in 1944 but did not meet expectations. NASA returned to the concept in the 1990s with an artificially stabilized model called BWB-17, built by Stanford University, which was flown in 1997 and showed good handling qualities. From 2000 NASA went on to develop a remotely controlled research model with a wingspan. NASA has also jointly explored BWB designs for the Boeing X-48unmanned aerial vehicle. Studies suggested that a BWB airliner carrying from 450 to 800 passengers could achieve fuel savings of over 20 percent. Airbus is studying a BWB design as a possible replacement for the A320neo family. A sub-scale model flew for the first time in June 2019 as part of the MAVERIC programme, which Airbus hopes will help it reduce CO2 emissions by up to 50% relative to 2005 levels.
Characteristics
The BWB form minimises the total wetted area - the surface area of the aircraft skin, thus reducing skin drag to a minimum. It also creates a thickening of the wing root area, allowing a more efficient structure and reduced weight compared to a conventional craft. NASA also plans to integrate Ultra High Bypass ratiojet engines with the hybrid wing body. The wide interior spaces created by the blending pose novel structural challenges. NASA has been studying foam-clad stitched-fabric carbon fiber composite skinning to create uninterrupted cabin space. A conventional tubular fuselage carries 12-13% of the total lift compared to 31-43% carried by the centerbody in a BWB, where an intermediate lifting-fuselage configuration better suited to narrowbody sized airliners would carry 25-32% for a 6.1% - 8.2% increase in fuel efficiency.
Increased fuel efficiency – 10.9% better than a conventional widebody
Lower noise – NASA audio simulations show a 15dB reduction of Boeing 777-class aircraft, while other studies show 22–42 dB reduction below Stage 4 level, depending on configuration.
Potential disadvantages
Evacuating a BWB in an emergency could be a challenge. Because of the aircraft's shape, the seating layout would be theatre-style instead of tubular. This imposes inherent limits on the number of exit doors.
In order to fully realise the potential advantages of the BWB design in a large aircraft, the engines are typically placed above the rear fuselage. Air safety authorities have expressed a concern that in an accident they could become detached and their momentum carry them forwards so that they fall onto the passenger cabin.
Passengers are unwilling to sit in windowless environments.
Passengers furthest from centerline will be subject to potential discomfort during wing roll. Extreme discomfort results in motion sickness.
At an American Institute of Aeronautics and Astronautics meeting on March 28, 2018 at the University of Washington in Seattle, Boeing's VP of Product Development and Future Airplane Development Mike Sinnett noted that as the center wingbox is also the passenger cabin, it needs to be tall enough to stand upright, translating into a large transport minimum span for multiple hundreds of passengers. For the same payload, a cargo BWB has more wingspan but is heavier empty and it is not worth it for short missions of around four or fewer hours, while long haul routes would see a benefit. However, the larger wing span may conflict with airport compatibility and containers quick loading: changing the infrastructure would need an economical improvement of more than 20% over current designs, except maybe for a military cargo aircraft. A tube-and-wing design is easier to stretch or shrink for several sub-types sharing the large development costs while a BWB can hardly be modified by its most expensive non-constant section in a non-constant way.
A concept photo of a blended wing body commercial aircraft appeared in the November 2003 issue of Popular Science magazine. Artists Neill Blomkamp and Simon van de Lagemaat from The Embassy Visual Effects created the photo for the magazine using computer graphics software to depict the future of aviation and air travel. In 2006 the image was used in an email hoax claiming that Boeing had developed a 1000-passenger jetliner with a "radical Blended Wing design" and Boeing refuted the claim.
