Blended wing body

A blended wing body (BWB), Blended body or Hybrid Wing Body (HWB) is a fixed-wing aircraft having no clear dividing line between the wings and the main body of the craft.[1] The aircraft has distinct wing and body structures, which are smoothly blended together with no clear dividing line.[2] This contrasts with a flying wing, which has no distinct fuselage. A BWB design may or may not be tailless.

Computer-generated model of the Boeing X-48

NASA's prototype of a Blended Wing aircraft

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 17-foot (5.2 m) model (6% scale) called BWB-17, built by Stanford University, which was flown in 1997 and showed good handling qualities.[3]^:16 From 2000 NASA went on to develop a remotely controlled research model with a 21-foot (6.4 m) wingspan.

NASA has also jointly explored BWB designs for the Boeing X-48 unmanned aerial vehicle.[4] Studies suggested that a BWB airliner carrying from 450 to 800 passengers could achieve fuel savings of over 20 percent.[3]^:21

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 (Model Aircraft for Validation and Experimentation of Robust Innovative Controls) programme, which Airbus hopes will help it reduce CO₂ emissions by up to 50% relative to 2005 levels.[5]

Characteristics

Spectrum of aircraft design concepts. From left to right: conventional airliner (Boeing 757), blended wing body (B-1 Lancer), flying wing with bulged fairings (B-2 Spirit), and almost clean flying wing (Northrop YB-49).

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 (UHB) ratio jet engines with the hybrid wing body.[6]

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.[7]

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.[8]

Potential advantages

Significant payload advantages in strategic airlift, air freight,[9] and aerial refueling roles
Increased fuel efficiency – 10.9% better than a conventional widebody[8]
Lower noise – NASA audio simulations show a 15dB reduction of Boeing 777-class aircraft,[10] while other studies show 22–42 dB reduction below Stage 4 level, depending on configuration.[1]

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.[11][12]
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.[13]

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.[14]

List of blended wing body aircraft

Type	Country	Class	Role	Date	Status	No.	Notes
Airbus Maveric	EU	UAV	Experimental	2019	Prototype	1	[15][16]
Boeing X-45	USA	UAV	Experimental	2002	Prototype	2
Boeing X-48	USA	UAV	Experimental	2007	Prototype	2
Lockheed A-12, M-21 and YF-12	US	Jet	Reconnaissance	1962	production	18	YF-12 was a prototype interceptor
Lockheed SR-71 Blackbird	US	Jet	Reconnaissance	1964	production	32
McDonnell XP-67	USA	Propeller	Fighter	1944	Prototype	1	Aerofoil profile maintained throughout.
Miles M.30	UK	Propeller	Experimental	1942	Prototype	1
Rockwell B-1 Lancer	USA	Jet	Bomber	1974	Production	104	Variable-sweep wing
Tupolev Tu-160	USSR	Jet	Bomber	1981	Production	36	Variable-sweep wing
Tupolev Tu-404	Russia	Propeller	Airliner	1991	Project	0	One of two alternatives studied
Westland Dreadnought	UK	Propeller	Transport	1924	Prototype	1	Mail plane. Aerofoil profile maintained throughout.

In popular culture

Popular Science concept art

Image of the "Boeing 797" from Popular Science, 2003

A concept photo of a blended wing body commercial aircraft appeared in the November 2003 issue of Popular Science magazine.[17] 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.[18] In 2006 the image was used in an email hoax claiming that Boeing had developed a 1000-passenger jetliner (the "Boeing 797") with a "radical Blended Wing design" and Boeing refuted the claim.[19][20][21]

References

Russell H. Thomas, Casey L. Burley and Erik D. Olson (2010). "Hybrid Wing Body Aircraft System Noise Assessment With Propulsion Airframe Aeroacoustic Experiments" (PDF). Retrieved 26 January 2013. Presentation Archived 2013-05-16 at the Wayback Machine
Crane, Dale. Dictionary of Aeronautical Terms, third edition. Newcastle, Washington: Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2. p. 224.
Liebeck, R.H. (January–February 2004). "Design of the Blended Wing Body Subsonic Transport". AIAA Journal of Aircraft. 41 (1). pp. 10–25.
"A flight toward the future." Archived December 4, 2012, at the Wayback Machine Boeing, August 7, 2012 Retrieved: November 23, 2012.
Reim, Garrett (11 February 2020). "Airbus studies blended-wing airliner designs to slash fuel burn". Flight Global.
Michael Braukus / Kathy Barnstorff (Jan 7, 2013). "NASA's Green Aviation Research Throttles Up Into Second Gear". NASA. Retrieved Jan 26, 2013.
Bullis, Kevin (January 24, 2013). "NASA has demonstrated a manufacturing breakthrough that will allow hybrid wing aircraft to be scaled up". MIT Technology Review.
Graham Warwick (Aug 22, 2016). "Finding Ultra-Efficient Designs For Smaller Airliners". Aviation Week & Space Technology.
Warwick, Graham. "Boeing works with airlines on commercial blended wing body freighter." Flight International, May 21, 2007.
Warwick, Graham (Jan 12, 2013). "Hear This - The BWB is Quiet!". Aviation Week.
E. R. Galea; L. Filippidis; Z. Wang; P. J. Lawrence; J. Ewer (2011). "Evacuation Analysis of 1000+ Seat Blended Wing Body Aircraft Configurations: Computer Simulations and Full-scale Evacuation Experiment". Pedestrian and Evacuation Dynamics. pp. 151–61. doi:10.1007/978-1-4419-9725-8_14. ISBN 978-1-4419-9724-1.
Galea, Ed. "Evacuation analysis of 1000+ seat Blended Wing Body aircraft configurations". evacmod.net (video). Retrieved August 25, 2015.
"Boeing not convinced by blended wing aircraft design". Institution of Mechanical Engineers. June 16, 2015.
"Don't look for commercial BWB airplane any time soon, says Boeing's future airplanes head". Leeham News. April 3, 2018.
"Airbus reveals its blended wing aircraft demonstrator", Airbus, 11 February 2020. (Retrieved 18 February 2020)
Caroline Delbert; "Will We One Day Fly in This 'Blended Wing' Airplane? Airbus Built a Prototype To Find Out", Popular Mechanics, 13 February 2020. (Retrieved 18 February 2020)
"Future of Flight." Popular Science, November 2003.
"Future Flight: A Gallery of the Next Century in Aviation." PopSci.com, October 15, 2003. Retrieved: November 22, 2012.
"New Boeing 797 Giant "Blended Wing" Passenger Airliner-Fiction!". TruthOrFiction.com. March 17, 2015.
Christensen, Brett M. "Boeing 797 Hoax" Hoax-Slayer, April 19, 2012. Retrieved: November 22, 2012.
Baseler, Randy. "Air mail." Boeing blogs: Randy's Journal, November 1, 2006. Retrieved: November 22, 2012.