BLENDED WING-BODY

TYPE: New-concept airliner.

PROGRAMME: In mid-1990s, shortly before absorption by Boeing, McDonnell Douglas released details of the BWB-1-1 (blended wing-body) study, giving the most comprehensive analysis yet of the flying wing’s advantages for very large transport aircraft. This work continued after merger with Boeing, with at least half-a-dozen BWB derivatives under consideration at the beginning of 2002, ranging in passenger capacity from 180 to 570. An earlier BWB incarnation, able to carry 800 passengers over a 7,000 n mile (12,964 km; 8,055 mile) range, gave predicted benefits that included a 12.5 per cent reduction in T-O weight and 12.3 per cent less empty weight; 27.5 per cent reduction in fuel burn; 27.0 per cent reduction in installed thrust; and 20.6 per cent better lift/drag. These gains achieved by increasing wing area by 27.9 per cent (reducing loading by 33.6 per cent) and having a 19.2 per cent greater span.
Tests of a radio-controlled 5.5 m (18 ft) span scale BWB-1-1 were undertaken by Stanford University at El Mirage dry lake, California, in July 1997 as part of a USD2.3 million programme to evaluate flight control laws for a flying wing. Data generated by these trials were of poor quality, but a series of tethered wind tunnel tests of a 3.7 m (12 ft 2 in) span free flight model conducted by NASA in 2005 yielded useful results.
In co-operation with NASA, Boeing initiated development of a 14 per cent scale vehicle known as the BWB-LSV (blended wing body—low speed vehicle) in the late 1990s. Powered by three Williams J24-8 turbojet engines, this featured a 10,67 m (35 ft) wing span and weighed approximately 1,361 kg (3,000 lb). Construction began in 2000, at which time it was still known as the BWB-LSV, but it was subsequently assigned the experimental X-48A designation shortly before the end of 2001. Production and assembly of the X-48A was expected to have been completed by the end of 2002, with a lengthy series of ground testing planned for most of 2003, leading up to flight trials in 2004. In the event, the X-48A was quietly cancelled, among the reasons cited being difficulties encountered with the flight control system and budgetary considerations on the part of NASA.
Despite this setback, Boeing still wished to demonstrate BWB flight control systems and next approached Cranfield Aerospace of the UK in 2003 with a request to construct two examples of a smaller 8.5 per cent scale remotely piloted test vehicle. Given the designation X-48B on 15 June 2005, this is to undergo a joint trials programme in the USA for Boeing, NASA and the US Air Force Research Laboratory.
The X-48B is approximately 7.0 m (23 ft) long, with a span of 6.2 m (20 ft 4 in) and a wing area of 9.29 m² (100 sq ft). Weight has been reported as 237 kg (523 lb), with estimated performance figures including a max speed of 118 kt (218 km/h; 135 mph), a max altitude of 3,050 m (10,000 ft) and about 40 minutes’ endurance. Power is provided by three 0.22 kN (50 lb st) model aircraft microjet engines and the X-48B features a total of 20 control surfaces on the wing trailing-edge, of which the outer ailerons are split surfaces, with the ability to function as drag rudders and speed brakes. In event of an emergency landing being necessary, a recovery parachute and airbag are installed, as is a spin recovery parachute for use in departure from controlled flight during a planned series of high AoA stall tests.
Cranfield Aerospace was also responsible for the supply of a control vehicle, but software for flight control was developed by Boeing's Phantom Works. Flight testing is to take place at NASA’s Dryden Research Center at Edwards AFB, California and will be undertaken by the second X-48B; ground checkout of this was under way at Dryden in late 2006, with a series of five flights scheduled for early 2007. Previously, some 250 hours of wind tunnel testing was completed by the first X-48B at NASA’s Langley, Virginia, facility between 7 April and mid-May 2006, with this craft then being transferred to Dryden to serve as a back-up vehicle for the flight test programme. Investigation of stall characteristics, spin and tumble, asymmetric thrust and ground effects are among the test objectives, in addition to studies of dynamic interaction between control surfaces, wing aerodynamics and inlet conditions.
One potential application considered by Boeing is a BWB tanker for multipoint aerial refuelling. Equipped with three ‘smart’ booms, two hose/drogue refuelling points and automated refuelling capabilities, BWB tanker would be able to accommodate simultaneous air-to-air refuelling of multiple conventional aircraft or UAVs. Fuel carried in wing tanks; maximum payload space would be available for up to 23 conventional pallets and 40 troops.
As a C2ISR (command, control, intelligence, surveillance, reconnaissance) platform, the BWB would provide increased loiter time, large interior space suitable for battle management control rooms, and ample exterior locations for conformal phased-array antennas for broadband communications with no increase in radar signature. These capabilities make the BWB additionally suitable as a long-range standoff weapons platform.
Other possible military derivatives could include a version to satisfy a future USAF cargo aircraft requirement.
Another organisation known to be conducting investigations into the Blended Wing Body configuration is the Hamburg University of Applied Sciences in Germany. This has conceived a design meant to represent a notional 900-seat airliner known as the AC 20.30 that could enter service in 2030. Project has involved construction of a radio-controlled 1:30 scale model, which flew for the first time at Itzehoe on 16 December 2003 and which undertook extensive wind tunnel testing at Dresden in September 2005 to provide data for additional flight trials.
Also in Germany, as part of EC's five-year EUR160 million Lufo III air transport technology development project, BWB-Demonstratormodell developed by Department of Conceptual Aircraft Design at Stuttgart University and Institut fiir Flugzeugbau, with assistance from Institut für Flugzeugbau, with assistance from Institut für Flugmechanik und Flugregelung and Steinbeis Transferzentrum Aerodynamik, Flugzeug- und Leichtbau. Single-jet model aircraft shown at ILA, Berlin, May 2006.
BWB configuration is also being investigated as a means of reducing the sound impact of aircraft in a study led by Cambridge University in the UK and Massachusetts Institute of Technology. Silent Aircraft Initiative SAX-40 is funded by the Cambridge-MIT Institute (CMI); launched in 2003 with a grant from CMI of GBP2.3 million; first public announcement 6 November 2006; includes teams involved in different aspects of aircraft design for a multidisciplinary approach; core personnel are 40 CMI researchers. Project has received significant collaborations from all parts of the civil aerospace/aviation industry including British Airways, BAA, Boeing, Brüel & Kjær, Civil Aviation Authority, Cranfield University, DHL, EasyJet, Eurocontrol, HACAN Clearskies, Lochard, London Luton Airport, Marshall of Cambridge Aerospace, National Air Traffic Services (NATS), Nottingham East Midlands Airport, Royal Aeronautical Society and Rolls-Royce.
Noise reduction measures concentrate on take-off, climbout and approach phases of flight. On departure, this is achieved by engines embedded within the fuselage with intakes above the wings to shield much of the engine noise from listeners on the ground; novel, ultra-high bypass engines with a variable-area exit nozzle which can operate for low noise with low-speed exhaust jets at take-off and during climb, and then be optimised for minimum fuel burn in cruise; thrust, nozzle settings and climb rate optimised for low noise, subject to meeting legal requirements; long engine exhaust ducts to provide space for extensive acoustic liners.
On approach, the airframe on a conventional aircraft is as noisy as the engines. SAX-40 approach noise is reduced by an airframe design that enables the aircraft to approach at lower speed and so land further down the runway; low-noise fairings on the landing gear; advanced aerofoil trailing-edge treatment; a deployable drooped leading-edge on the wings and vectored thrust, which are used to enable low-speed flight without noise penalty; absence of flaps and slats; engines having a low idle thrust and able to respond rapidly if a go-around is necessary.
SAX-40 is a 215-seat (three-class) ‘all-lifting’ design, producing lift on centrebody as well as wings; makes use of a novel centrebody shape with leading edge carving; this balances aerodynamic forces without the need for tail surfaces, and enables an optimal wing design with an elliptical lift distribution and low cruise drag. Performance includes 149 passenger-miles per Imperial gallon of fuel (compared with about 120 for the best current aircraft in this range and size). This is equivalent to the Toyota Prius Hybrid car carrying two passengers. Noise of 63 dBA outside airport perimeter - some 25dB quieter than current aircraft.
Notional engines are ‘Granta-3401’. Single core driving three high-capacity, low-speed fans. Distributed propulsion system is designed to ingest centrebody boundary layer, which reduces the fuel burn. Multiple small fan design is easier to embed in the airframe and leads to reduced weight and nacelle drag; also enhances boundary layer ingestion, thereby improving fuel efficiency, and the low fan tip speeds produce low noise. Ultra-high bypass ratio 18.3 at take-off for low jet noise, 12.3 at top of climb for good efficiency.
Several possible Boeing BWB derivatives have emerged as candidates for production. including the BWB-250, with accommodation for about 260 passengers, and the BWB-450 with room for about 480 passengers.
Estimated data below refer to the 800-seat Boeing BWB-1-1 proposal powered by three 275 kN (61,900 lb st) turbofans and CMI SAX-40 with three ‘Granta-3401’ engines.

DIMENSIONS, EXTERNAL:

  • Wing span: excl winglets, BWB-1: 85 m (280 ft)
    • incl winglets: BWB-1: 88 m (289 ft)
    • SAX-40: 67.54 m (221 ft 7 in)
  • Wing aspect ratio: BWB-1: 5.1
    • SAX-40: 5.5
  • Length overall, BWB-1: 49 m (161 ft)
  • Height overall, BWB-1: 15 m (50 ft)

AREAS:

  • Wings: trap, BWB-1: 728 m² (7,840 sq ft)
    • gross: BWB-1: 1,423 m² (15,325 sq ft)
      • SAX-40: 835.9 m² (8,998 sq ft)

WEIGHTS AND LOADINGS:

  • Weight empty, BWB-1: 167,750 kg (369,800 lb)
  • Weight empty, equipped: BWB-1: 186,900 kg (412,000 lb)
    • SAX-40: 94,190 kg (207,660 lb)
  • Max payload: BWB-1: 104,800 kg (231,000 lb)
    • SAX-40: 23,405 kg (51,600 lb)
  • Max fuel weight: BWB-1: 122,500 kg (270,000 lb)
    • SAX-40: 33,252 kg (73,310 lb)
  • Max T-O weight: BWB-1: 373,300 kg (823,000 lb)
    • SAX-40: 150,840 kg (332,550 lb)
  • Max zero-fuel weight, BWB-1: 291,650 kg (643,000 lb)
  • Fuel burn over 7,000 n miles with 800 passengers, BWB-1: 96,820 kg (213,450 lb)
  • Max wing loading: BWB-1: 513 kg/m² (105 lb/sq ft)
    • SAX-40: 180.4 kg/m² (36.96 lb/sq ft)
  • Max power loading, BWB-1: 452 kg/kN (4,4 lb/lb st)

PERFORMANCE:

  • Normal cruising speed: BWB-1: M0.85
    • SAX-40: M0.8
  • Max approach speed, BWB-1: 150 kt (278 km/h; 173 mph) EAS
  • Initial cruising altitude: BWB-1: 10.665 m (35.000 ft)
    • SAX-40: 12,190 m (40,000 ft)
  • T-O field length, BWB-1: 3,353 m (11,000 ft)
  • Range: with 800 passengers, BWB-1: 7,000 n miles (12,964 km; 8,055 miles)
    • with 215 passengers, SAX-40: 5,000 n miles (9,260 km; 5,753 miles)