Seminar report on Blended Wing Body by akfunworld

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Here's the seminar report on 'Blended Wing Body' made by me. Enjoy...

Text of Seminar report on Blended Wing Body by akfunworld

Blended Wing Body

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Page 1

Blended Wing Body Chapter 1 INTRODUCTION1.1 Classification of Aircraft Wing ConfigurationsThe different types of wing configuration used in an Aircraft are1. Conventional Configuration: Tube and Wing or Tail Aft. 2. Blended Wing Body (BWB) 3. Hybrid Flying Wing 4. Flying Wing 5. The Boeing C Wing

Fig. 1.1 Aircraft wing Configurations. Here well concentrate more on Blended Wing Body which is the topic of this Seminar.

1.2 Blended Wing Body (BWB)Blended Wing Body (BWB) aircraft have a flattened and airfoil shaped body, which produces most of the lift, the wings contributing the balance. The body form is composed of distinct and separate wing structures, though the wings are smoothly blended into the body.

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Blended Wing BodyBy way of contrast, flying wing designs are defined as a tailless fixed-wing aircraft which has no definite fuselage, with most of the crew, payload and equipment being housed inside the main wing structure. Blended wing body has lift-to-drag ratio 50% greater than conventional airplane. Thus BWB incorporates design features from both a futuristic fuselage and flying wing design. The purported advantages of the BWB approach are efficient high-lift wings and a wide airfoilshaped body. This enables the entire craft to contribute to lift generation with the result of potentially increased fuel economy and range.

Fig. 1.2 Computer generated model of BWB.

1.2.1 History of BWBA flying wing is a type of tail-less aircraft design and has been known since the early days of aviation. Since a wing is necessary of any aircraft, removing everything else, like the tail and fuselages, results in a design with the lowest possible drag. Successful applications of this configuration are for example the H-09 and later H-0229 developed by Horton Brothers for Nazis during 1942. Latter Northrop started designing flying such as NIM in 1942 and later XB- 35 Bomber which flew first in 1942. In 1988, when NASA Langley Research Centres Dennis Bushnell asked the question: Is there a renaissance for the long haul transport? there was cause for reaction. In response, a brief preliminary design study was conducted at McDonnell Douglas to create and evaluate alternate configurations. A preliminary configuration concept, shown in Fig. 1.4, was the result. Here, the pressurized passenger compartment consisted of adjacent parallel tubes, a lateral extension of the double-bubble concept. Comparison with a conventionalFor more visit- www.akfunworld.co.nr Page 3

Blended Wing Bodyconfiguration airplane sized for the same design mission indicated that the blended configuration was significantly lighter, had a higher lift to drag ratio, and had a substantially lower fuel burn.

In modern era after B-2 Bomber (1989) blended wing body was used for stealth operations. The unmanned combat air vehicle (UCAV) named X-47 in year 2003 was subjected to test flights. Flight test began on 20th July and the first flight reached an altitude of 7500 feet MSL (2286 m) and lasted for 31 min. On 4th September first remotely piloted aircraft was stalled. Latest being the NASA and Boeing successfully completed initial flight testing of Boeing X-48B on March 19, 2010.

The Blended Wing Body (BWB) is the relatively new aircraft concept that has potential use as a commercial or military use aircraft, cargo delivery or as fuel tanker.

Fig. 1.3 Development of aircraft design.

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Blended Wing Body

Fig. 1.4 Early blended configuration concept.

1.2.2 How BWB differs from flying wing design?Flying wing designs are defined as having two separate bodies and only a single wing, though there may be structures protruding from the wing. But blended wing body aircraft have a flattened and airfoil shaped body, which produces most of the lift to keep itself aloft, and distinct and separate wing structures, though the wings are smoothly blended in with the body.

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Page 5

Blended Wing Body Chapter 2

FORMULATION OF BWB CONCEPTNASA Langley Research Centre funded a small study at McDonnell Douglas to develop and compare advanced technology subsonic Transports for the design mission of 800 passengers and a 7000-n mile range at a Mach number of 0.85.Composite structure and advanced technology turbofans were utilized.

Defining the pressurized passenger cabin for a very large airplane offers two challenges. First, the square-cube law* shows that the cabin surface area per passenger available for emergency egress decreases with increasing passenger count. Second, cabin pressure loads are most efficiently taken in hoop tension. Thus, the early study began with an attempt to use circular cylinders for the fuselage pressure vessel, along with the corresponding first cut at the airplane geometry. The engines are buried in the wing root, and it was intended that passengers could egress from the sides of both the upper and lower levels. Clearly, the concept was headed back to a conventional tube and wing configuration. Therefore, it was decided to abandon the requirement for taking pressure loads in hoop tension and to assume that an alternate efficient structural concept could be developed. Removal of this constraint became pivotal for the development of the BWB.

Passenger cabin definition became the origin of the design, with the hoop tension structural requirement deleted. Three canonical forms shown in Fig 2.1a, each sized to hold 800 passengers were considered. The sphere has minimum surface area; however, it is not stream lined. Two canonical stream lined options include the conventional cylinder and a disk, both of which have nearly equivalent surface area. Next, each of these fuselages is placed on a wing that has a total surface area of 1393.54 sq-m. Now the effective masking of the wing by the disk fuselage results in a reduction of total aerodynamic wetted area of 650 sq-m compared to the cylindrical fuselage plus wing geometry, as shown in Fig 2.1b. Next, adding engines (Fig 2.1c) provides a difference in total wetted area of 947.6 sq-m. (Weight and balance require that the engines be located aft on the disk configuration.) Finally, adding the required control surfaces to each configuration as shown in Fig 2.1d results in a total wetted area difference of 1328.5 sq-m, or a reduction of 33%. Because the cruise lift to dragFor more visit- www.akfunworld.co.nr Page 6

Blended Wing Bodyratio is related to the wetted area aspect ratio, the BWB configuration implied a substantial improvement in aerodynamic efficiency.

Fig. 2.1 Genesis of BWB concept

Modern supercritical airfoils with aft camber and divergent trailing edges were assumed for the outer wing, whereas the centre body was to be based on a reflexed airfoil for pitch trim. A proper span load implies a relatively low lift coefficient due to the very large center body chords. Therefore, airfoilLW102Awas designed along with a planform indicating how pitch trim is accomplished via center body reflex; whereas the outboard wing carries a proper span load all of the way to the wingtip. Blending of this center body airfoil with the outboard supercritical sections yielded an aerodynamic configuration with a nearly elliptic span load. At this early stage of BWB development, the structurally rigid center body was regarded as offering free wingspan. Outer wing geometry was essentially taken from a conventional transport and bolted to the side of the center body. The result was a wingspan of

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Page 7

Blended Wing Body106.28 m., a trapezoidal aspect ratio of 12, and a longitudinal static margin of -15%, implying a requirement for a fly-by-wire control system.

The aft engine location, dictated by balance requirements, offered the opportunity for swallowing the boundary layer from that portion of the center body upstream of the inlet, a somewhat unique advantage of the BWB configuration. In principle, boundary-layer swallowing can provide improved propulsive efficiency by reducing the ram drag, and this was the motivation for the wide mail-slot inlet. However, this assumed that such an inlet could be designed to provide uniform flow and efficient pressure recovery at the fan face of the engine(s). Two structural concepts (Fig 2.2) were considered for the center body pressure vessel. Both required that the cabin be composed of longitudinal compartments to provide for wing ribs 3.81 m. apart to carry the pressure load. The first concept used a thin, arched pressure vessel above and below each cabin, where the pressure vessel skin takes the load in tension and is independent of the wing skin. A thick sandwich structure for both the upper and lower wing surfaces was the basis for the second concept. In this case, both cabin pressure loads and wing bending loads are taken by the sandwich structure. A potential safety issue exists with the separate arched pressure vessel concept. If a rupture were to occur in the thin arched skin, the cabin pressure would have to be borne by the wing skin, which must in turn be sized to carry the pressure load. Thus, once the wing skin is sized by this condition, in principle there is no need for the inner pressure vessel. Consequently, the thick sandwich concept was chosen for the center body structure. Passengers are carried in both single and double deck cabins, and the cargo is carried aft of the passenger cabin. As a tailless configuration, the BWB is a challenge for flight mechanics. Future generations of BWB designs would begin to address constraints not observed by this initial concept, but the basic character of the aircraft persists to