blended wing bodies

8/3/2019 Blended Wing Bodies

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By Bh.Phanindra Kumar

07521A0335


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The goal of aircraft design is to achieve safe andefficient flight. In the world of commercial airtransport, efficient, economically attractiveconfigurations are needed.

New technologies are being implemented in everysector now-a-days.Like ways, the aero sector has been

seeing vast changes in its development due to theadvancements in technology over the years.

One of such technologies is the Blended Wing Bodydesign for the modern aircrafts.

The evolution of the BWB dates

back to the medieval of the

19th century.


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1) Conventional Configuration: "Tube and Wing" or "Tail Aft"2) Blended Wing Body (BWB)3) Hybrid Flying Wing4) Flying Wing5) The Boeing C wing


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What is a Blended wing body concept ?

Blended Wing Body, or BWB,

designates an alternative airframedesign which incorporates designfeatures from both a futuristicfuselage and flying wing design. Thepurported advantages of the BWB

approach are efficient high-liftwings and a wide airfoil-shapedbody. This enables the entire craftto contribute to lift generation withthe result ofpotentially increasedfuel economy.

The airplane concept blends thefuselage, wing, and the engines intoa single lifting surface, allowing theaerodynamic efficiency to be

maximized


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History of BWB:

A 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 for any

aircraft, removing everything else, like the tail and the fuselage, results ina design with the lowest possible drag. Successful applications of this

configuration are for example the H-09 and latter H-0229 developed by

the Horton brothers for Nazis during 1942. Latter Northrop started

designing flying such as NIM in 1942 then latter XB-35 bomber that

flew first in 1946, and the stealthy B-2 bomber that flew first in 1989.

H09 1939

H0229

1942

1946 XB-35

bomber

YB-49 1949 B-2 bomber 1989


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In modern era after B-2 bomber blended wing

body was used for stealth operations. The

unmanned combat aerial vehicle (UCAV) in the year

2003 X-47 was subjected to test flights. Flight testsbegan on July 20, 2007 - the first flight reached an

altitude of 7,500 feet MSL (2,286 m) and lasted 31

minutes.. NASA and Boeing successfully completed

initial flight testing of the Boeing X-48B on March

19 2010.

The Blended Wing Body (BWB) is a relatively

new aircraft concept that has potential use as a

commercial or military transport aircraft, cargo

delivery or as fuel tanker

X-47A (UCAV) 2003

X-48 B 2007


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Basic configuration and nomenclature of

Boeing BWB 450


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BWB-450 specifications:


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BWB advantages compared to today's

advanced aircraft


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B-2 bomber specifications

Crew: 2

Length: 69 ft (21.0 m)

Wingspan : 172 ft (52.4 m)

Height: 17 ft (5.18 m)

Wing area: 5,140 ft (478 m)

Empty weight: 158,000 lb (71,700 kg)

Loaded weight: 336,500 lb (152,200kg)

Max take off weight : 376,000 lb(170,600 kg)

Powerplant: 4 general electricf111-GE100 non-afterburning turbaofans, 17,300 lbf (77 kN) each


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What makes B-2 bomber a stealth configuration:

It continuously changes shape when looked from different toconfuse radar

Whatever beams are locked onto it are either get reflected in

outer space or reduced or dissipated into nothing

Coated with special RAM (radar absorbing material ) such as

carbon fiber composite and top secret reflective paint to reduce

detection from enemy.

Electronic counter measure for jamming radar makes it

undetectable aircraft.

RCS (radar cross section ) is 1000 times less then B-52 bomber

It has special exhaust vents on top of which when hot gases are

mixed with cooler air make it almost undetectable to heat

seeking SAM(surface to air missile )


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Design cycle:


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This is the wind tunnel for performing all the tests for a BWB.

Analysts from NASA and Boeing will be testing the flights

and analyze its results.

This is the NASA Langleys Aeronautics Research Mission

Directorate where the tests for BWB ships are being done for

several years.

The effort has been funded primarily by Boeing, with some

money to support the flight test program coming from the Air

Force Research Lab (AFRL) at Wright Patterson AFB, Ohio.

Dryden is providing facilities and support for the flight test

under contract, as Langley did for the wind tunnel portion

of the prototype program.

Similar tests for noise, efficiency, other criteria are performed

for the BWBs.


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Alternate Fuels:Necessity to look for alternate fuels is one of the

major criterion for the futuristic models of any type. Therefore alternate

fuels like Synthetic fuels, Bioorganic fuels and Cryogenic fuels are to be

used according to the suitability.

Fossil fuels used in the aviation industry like Jet-A

produce carbon emissions, which contribute to roughly 2% of the global

carbon emissions. There is widespread call to reduce these emissions.

Synthetic fuels is not suitable due to the fact that the emission of the

extraction process themself are creating pollution. Although they can

be subsidized by other processes it is harmful.

Bioorganic fuel fuels are best for use in this type. Bio-fuels need to be

developed and have to be especially tailored for jet aircraft

applications, which are termed as biojet. Another major challenge of

pure biojet fuel is its poor high temperature stability characteristics in

the engine. The alternative to this problem is to use a mixture of

biofuels and jet fuel.

Cryogenic fuels are to be tested for their usability in usage by various

researches.


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There are certain causes for the noise in a conventional

aircraft. Some of them are below and the remedies for such

problems too

Noise by engine position: Engine noise reduces as by pass

ratio increases. The mixing of high energy hot air with

surrounding air is uniform and not sudden, exhaust noise

reduces to a great extent. The solution is to place engine halfabove and half below the wings to enhance the BLI.

Airframe: there is reduction in noise since

there are no tail aft, fuselage, or hanging

engines which are main contribution ofnoise.

Landing Gear Fairings: Fairings are

produce smooth outline and reduce drag.

Fairings when used in landing gear resiult

in reduction in noise.


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Other Features: tabs are small protrusions

at nozzle exit. There are delta wing like

structures like stream vortex generators

that increase mixing of jet & surrounding

air. Other devices are Chevrons which are

saw toothed structures enabling free

mixing of exhaust & air. They are larger

than tabs with same principle.


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Clearly the BWB shows a significant

advantage over a conventional aircraft

in terms of performance and weight.

However, the BWB is a revolutionaryaircraft concept and will require a

large and expensive engineering effort

to become a reality. Most likely, before

being used as a transport aircraft, it

will be utilized for military

applications. In fact, Boeing and the US

military are designing the BWB to be

used as an advanced tactical transport

and as an air refuel tanker The BWB

has a large fuselage and can carry

massive amounts of fuel. Also, it canprovide two permanent refueling

boom stations, rather than one as in

the KC-135, KC-10 or KC-767.A Boeing BWB tanker with pylon-mounted engines (picture fromBoeing).


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Flying wing challenges:

1. Cabin pressurization is one of several design challenges facing the BWB.

2. The BWB, however, has a unique shape that requires a novel approach to

satisfy pressurization and structural needs.

3. The design uses ten intermediate chord-wise (front-to-back) ribs to connect

the upper and lower wing skins. These ribs separate the interior into ten

passenger bays.

4. Advanced composite material will be required to minimize the amount of

structure needed to withstand the pressurization loads and deflections in

the skins.

5. Open certification problems : unstable configuration , ditching

6. Open design problems : rotation on take-off, landing gear integration,


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Recommendations for further study: The BWB concept incorporates features that are pretty much new to the

present aircraft technology. Extensive research is needed in the areas of

manufacturing technology, structures ad materials. Issues like cabin pressurization are very crucial, which if does not satisfy

the basic requirements of a passenger will make it unsuitable as a

passenger aircraft. Therefore it demands a very keen attention.

The control of a BWB is not as easy as controlling the aircrafts of today.

Also the BWB maneuvers cause undesirable reactions on passengers

affecting their comfort level greatly. This needs to be catered while

devising the control laws.

Airport infrastructure has to be revolutionized, to accommodate the wide

BWBs and also, the large flow of passengers expected with an

exponentially increasing air-traffic. Runway width has to necessarily

increase for the wide body BWBs. Safety is a significant criterion that has to be ensured. Design and

positioning of emergency exit doors needs careful attention keeping in

mind the crowd behavior in a cabin layout that does not favor easy crowd

control.


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The BWB is a revolutionary, but viable concept that has a

great potential to cater to the needs of the future. In a timeafter fifty years, when fuel costs would be intolerably high,

even with a blend of alternative fuels, BWBs lesser fuel

consumption will be a very great boon. The environmental

restrictions in terms of emissions and noise would be even

more stringent, which might completely rule out theoperation of the present aircrafts, in which case, a radical

design like that of a BWB with its reduced noise and

emissions would save the era.

CONCLUSION:

blended wing bodies

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