-- 0 --

TABLE OF CONTENTS

Page

1. Introduction 1

2. Boeings X-48B 4

3. Characteristics of X-48B 6

4. Operation of Boeings X-48B 6

5. Drawbacks of Boeings X-48B 8

6. Boeings X-48C 9

7. Conclusion 11

8. References 12

-- 1 --

1. INTRODUCTION

The aircraft market is a fast growing but also competitive business. Therefore the aircraft

building companies invest a lot of effort into the research for new aircraft configurations to be

one step ahead of the other companies to accomplish the given constraints and requirements for

the aircraft market of tomorrow. Over the next 50 years, increased demand for air travel,

combined with economic and environmental pressures, will create a turnover point for game-

changing aircraft designs to move from the drawing board into production. Figure 1 describes

few images of present available aircraft configurations that were built by different companies to

meet the demands of the world market with minimal disturbance to the Mother Nature.

The above mentioned designs are not at all new. Even the Flying wings have been around since

the 1930s and 40s (Northrop Flying Wing, Armstrong-Whitworth AW-52 and Horten Ho-2), but

developments in materials and computer-aided fly-by-wire control systems have started to make

them economically and technologically plausible.

With all the experiments and researches carries out by the aerospace industries, Boeing is one of

the companies that have taken the necessary steps rapidly to meet the needs of the customers

around the world today. They have a legacy of introducing many next-generation systems to the

aerospace industry. One of the latest results of these researches is the Blended Wing Body

aircraft (BWB). This particular model is expected to use 20-25% less fuel, require 10-15% less

weight (or conversely allow for more paying payload) and would result in 10-15% lower direct

operating costs when compared with a conventional airliner. It carries the shape of a manta ray

that is shown in Figure 2.

Figure 1 Different aircraft configurations

Blended Wing Body (BWB) Conventional Configuration Hybrid Flying Wing (HFW) Flying Wing

-- 2 --

Figure 2 Manta ray that resembles BWB

The Blended Wing Body (BWB) aircraft configuration is employed with a radical new design of

the traditional tube-and-wing aircraft which offers revolutionary improvement in performance

and efficiency over current-day airframe configurations. A BWB configuration is characterized

by an overall aircraft design that provides distinction between wings and fuselage and fuselage

and tail. The BWB configurations are closely resembles the flying wing configuration.

The BWB configuration is such that the wings blend smoothly into a wide flat, air foil shaped

and tailless fuselage. This concept incorporates a blend between a conventional airplane and a

flying wing design. Its wide fuselage produces most of the aircraft lift with the wings

contributing the balance. Thus the fuselage is designed like a lift producing air foil for even

small angles of attack. This configuration enables the entire aircraft to contribute to the lift with

less drag compared to the conventional cylindrical fuselage. The BWB is said to have a 50%

greater lift-to-drag ratio when compared to a conventional airplane. The result of this is

increased fuel economy and range.

Figure 3 Blended Wing Body

-- 3 --

The BWB aircraft has a smaller surface area compared to the conventional aircraft design; which

will cause accumulation of less drag. In addition, without the body wing which could be found

between the tail wing and body in the conventional aircraft design, the overall surface is less

angular. Therefore the BWB will undergo much lower interference drag.

While the primary benefit of the blended wing body design comes from the large aerodynamic

gain, there are structural advantages due to the integration of the wing structure with the thick

central body. This integration means that the maximum wing bending moment and shear are

estimated to be about half of that for the conventional configuration, implying potential

structural weight saving.

The unique configuration of the BWB offers several promising advantages over other

conventional configurations including: high internal volume, aerodynamic efficiency, structural

efficiency, and lower noise. In a civil transport role, the BWB offers a large improvement in

cost-per-seat-mile, which is a critical parameter for airline viability measurements. Also the high

volume in the centre section of the aircraft allows large cargo volume with high operating

efficiency. As a tanker, the configuration carries the same advantage as the freighter and is even

well-suited for transporting the low-density methane and hydrogen fuels that are currently being

considered for future propulsion concepts.

Boeing is looking forward to make the BWB the next revolutionary design of a commercial

airliner which would carry more passengers than their biggest airliner 747. The Figure 4 shows

the size comparison of Boeing 747 and the modelled BWB by Boeing.

Figure 4 Modeled Blended wing body and conventional

airplane structure together one on one

-- 4 --

Figure 4 Boeing X-48 B

2. BOEINGS X-48B

NASA joined hands with Boeing in the year of 2007 to develop advanced concepts for aircraft

that could meet specific energy, efficiency, environmental and operation goals in 2030 and

beyond. The studies were intended to identify key technology developments to enable the

proposed advanced airframes and propulsion systems. The BWB programme of NASA in

collaboration with Boeing was known as X-48 and the engineers were looking forward for an

aircraft three generations beyond todays commercial fleet.

Boeings X-48B BWB aircraft was initially developed as a study of the structural, aerodynamic

and operational advantages of the airframe design, a mix between a conventional plane and a

flying wing design, for potential use as a remotely controlled military vehicle. When X-48B and

a Flying wing are compared, flying wing has no definite fuselage and it contains only a single

wing with the payload carried within the thickness of the wing. The X-48B model is an

evolution of this design, blending the fuselage, wings and engines into a single lifting surface,

producing an aircraft with increased aerodynamic efficiency while maintaining the required

payload space which was previously a design issue with Flying Wings.

NASA used the generational categories to priorities its research, with each generation setting

more stringent environmental targets for fuel burn, emissions, noise and field length. Equating to

reductions exceeding 70% in fuel burn, 75% in emissions, and 71dB in noise relative to todays

aircrafts, X-48 has become one of the most demanding because all the goals must be met

simultaneously.

-- 5 --

Robert Hauschild Liebeck is the Boeings BWB program manager who developed the design of

the BWB. He is an American aerodynamicist, professor and aerospace engineer at the Boeing

Company. He is best known for his contributions to aircraft design and his aerodynamic airfoil

designs known as the "Liebeck airfoil". Even during the Cold War, he designed wings for high

altitude airplanes. He has even designed wings that boost performance of racing cars for

Indianapolis and Formula 1 and also the keel section for the yachts.

The X-48B Low Speed Vehicle (LSV) is an 8.5%-scale version of a full-scale blended-wing-

body aircraft designed to investigate the stability and control characteristics of this aircraft

configuration. Two flight vehicles have been built. The first vehicle (LSV-1) was tested in wind-

tunnel tests to obtain aerodynamic and stability data. The second vehicle (LSV-2) was

constructed as the primary flight vehicle and is the subject of the flight test program.

Boeings design integrates the engines into the rear of the aircraft, reducing the overall drag of

the aircraft due to the reduction in surface area. The embedded engines can ingest the slower

moving air that is present in the wake of the fuselage. This technique enables the engines to use

less fuel for the same amount of thrust. Furthermore, positioning the engine on the upper surface

means that the body of the aircraft deflects the engine noise upwards, making the aeroplane

quieter.

Figure 5 Robert Hauschild Liebeck - Aerospace Engineer at Boeing Co.

-- 6 --

3. CHARACTERISTICS OF X-48B

Crew: As X-48B is a remotely controlled it carries no crew members.

Wing span: 20 ft 5 in (6.22 m)

Wing area: 100.5 sq ft (9.34 m2)

Gross weight: 500 lb (227 kg)

Air frame: Composite material

Power plant: Three Jet Cat P200 turbojet, 52 lbf (0.23 kN) thrust each

Maximum speed: 136 mph or 219 km/h (120 kn)

Endurance: 40 minutes

Service ceiling: 10,000 ft (3,048 m)

Model scale: 8.5% scale version of a conceptual 240 foot wide design.

Successful flight tests: 92 flights between the years 2007-2010

4. OPERATION OF BOEINGS X-48B

Boeing partnered with NASAs fundamental aeronautics program and the air force research

laboratory to study the structural, aerodynamic and operational advantages of the BWB concept.

On the completion of the 8.5% scaled prototype of X-48B in 2006, it was moved to NASA

Langley Research Centre in Hampton where the researchers conducted wind tunnel tests on X-

48B prototype aircraft to evaluate the design's stability, control and spin/tumble characteristics.

The model aircraft uses a hybrid shape that resembles a flying wing, which also incorporates

some features of a conventional airliner. The airframe is a unique merger of efficient advanced

wings and a wide air foil-shaped body, which causes the aircraft to generate high lift-to-drag

ratios, thereby increasing fuel economy. The aircraft is also built using advanced lightweight

composite materials and which weighs about 500 pounds. Three Jet Cat P200 turbojet engines

were utilized to Power the aircraft which could fly up to 120 knots (138 miles an hour) in a low-

speed configuration and as high as 10,000 feet during flight-testing. The data obtained from

these tests were used to develop flight control laws and help define the flight research program.

On the completion of the tests on X-48B performed in wing tunnel, the demonstrators began

flight tests at NASA's Dryden Flight Research Centre in early 2007 and the testing was

continued till the end of 2008. The remotely controlled X-48B BWB aircrafts first ever test

-- 7 --

flight was successfully carried out on 20th

of July 2007. The operators managed to fly it in air for

nearly 31 minutes and made it to climb up to an altitude of 7,500 ft. The pilot was located at a

ground control station where he could remotely pilot the vehicle using conventional aircraft

controls with the help of a forward-looking camera on board. The flight tests are intended in part

to validate the results of those wind tunnel tests which successfully did.

After the first six highly successful flight test, the aircraft went under a four weeks of

maintenance and planned modifications to replace extended slat leading edges with slat less

leading edges and update the flight control software. This helped the team to evaluate the

aircrafts flight conditions in a slats-retracted configuration.

The wing tips of X-48B model utilizes a winglet which can also be seen in a conventional

airliner. The winglets are usually intended to improve the efficiency of fixed-wing aircraft, but

BWB also utilizes it to achieve the similar performance. There are several types of wingtip

devices, and although they function in different manners, the intended effect is always to reduce

the aircraft's drag by partial recovery of the tip vortex energy. Wingtip devices can also improve

aircraft handling characteristics and enhance safety for following aircraft. Such devices increase

the effective aspect ratio of a wing without materially increasing the wingspan. Wingtip devices

increase the lift generated at the wingtip by smoothing the airflow across the upper wing near the

tip and reduce the lift-induced drag caused by wingtip vortices, thus improving lift-to-drag ratio.

This increases fuel efficiency in powered aircraft and increases cross-country speed in gliders, in

both cases increasing range. The Figure 7 shows the effect of the presence of winglet at the wing

tip.

Figure 6 A successful flight of X-48B

-- 8 --

5. DRAWBACKS OF BOEINGS X-48B

Even though the X-48B model made 92 successful test flights, it was carried out to gather more

information on structural, aerodynamic and operational advantages of the airframe design.

Researchers still face several challenges in developing a full production model of the Boeing

Blended Flying Wing. The main drawback to the BWB concept is that it lacks control surfaces

and conventional stabilising surfaces such as a tail making it unstable and difficult to control.

Therefore, this function has to be fulfilled by the flying wing or the blended wing body itself.

Further difficulties has risen from the problem of fitting the pilot, engines, flight equipment and

payload all within the depth of the wing section. A wing that is deep enough to contain all these

elements will have an increased frontal area, when compared to a conventional wing and

fuselage, which in turn results in higher drag counteracting the drag advantages of the design.

Cabin pressurisation will pose a problem in the flying wing's much larger cabin. It will require

the development of a new pressurisation system. The large cabin and small exterior surface area

could also cause an issue in emergency evacuation situations.

Other than the technical issues, Boeing may face a problem in incorporating this design into the

commercial sector. The design is visually very different from the traditional conventional

aircraft design; because of this the public may hesitate about getting on an aircraft with such a

different design from the status. Most passengers won't have a window, so the aircraft may have

to introduce more entertainment on board or implement a system which allows passengers time

to see out of the aircraft.

Figure 7 Effect of presence of a winglet

-- 9 --

6. BOEINGS X-48C

Boeing's X-48B aircraft was modified into the X-48C for research for NASA's Environmentally

Responsible Aviation, or ERA, project. The X-48C modified version successfully flew for the

first time on 7th

of August 2012 at Edwards Air Force Base. This designed aircraft is also a result

of the partnership of Boeing Company with NASA.

The new X-48C model was modified to evaluate the low-speed stability and control of a low

noise version of a notional, future Hybrid Wing Body (HWB) aircraft design. The HWB design

stems from concept studies being conducted by NASA's Environmentally Responsible Aviation

project of future potential aircraft designs 20 years from now.

Primary changes to the "C" model from the "B" model were intended to transform it into an

airframe noise shielding configuration. External modifications included relocating the wingtip

winglets inboard next to the engine exhaust ducts, effectively turning the winglets into twin

vertical tails. The aft deck of the aircraft was extended about two feet to the rear. Finally, the

project team replaced the X-48B's three 50-pound thrust jet engines with two 89-pound thrust

engines.

Since handling qualities of the X-48C are different from those of the X-48B, the project team

developed flight control system software modifications, including flight control limiters to keep

the airplane flying within a safe flight envelope. This will enable a stronger and safer prototype

flight control system suitable for future full scale commercial hybrid or blended wing aircraft.

Figure 8 Left side: Boeings X-48B demonstrator, Right side: Boeings X-48C demonstrator

-- 10 --

The X-48C retains most dimensions of the B model, with a wingspan just longer than 21 feet,

and a weight of about 500 pounds. The aircraft has an estimated top speed of about 140 mph

(225 km/h), and a maximum altitude of 10,000 feet. The X-48C model has completed 30

successful test flights at NASAs Dryden Flight Research Center. Most the test flights lasted

around 30 minutes. It made its final test flight on 12th

April, 2013.

NASA plans to use the data gathered over the campaign to aid in the design of future green

airliners that are quieter and more fuel-efficient than conventional aircraft, while Boeing is

touting the design's potential military applications.

Figure 9 End results of Boeings X-48 aircraft demonstrators

-- 11 --

7. CONCLUSION

After flying the remotely piloted X-48B and X-48C Hybrid / Blended Wing Body research

aircraft for nearly seven years (2006-2013), the joint NASA-Boeing X-48 project team

completed a highly successful and productive flight test project at NASAs Dryden Flight

Research Centre.

The manta-shaped X-48 Hybrid Wing Body technology demonstrator flew a total of 122 flights,

92 of the B-model and 30 of them as the C-model. The last flight of the X-48C occurred on 9th

April, 2013 with having first flown eight months ago on 7th

August, 2012.

We have accomplished our goal of establishing a ground to flight database, and proving the low

speed controllability of the concept throughout the flight envelope, mentioned Fay Collier,

manager of NASAs Environmentally Responsible Aviation project. (Quick, 2013)

Both very quiet and efficient, the hybrid wing body has shown promise for meeting all of

NASAs environmental goals for future aircraft designs, Collier said. (Quick, 2013)

The aircraft, designed by The Boeing Co. and built by Cranfield Aerospace Limited of the

United Kingdom, was flown in partnership with NASA. The X-48C model, which was formerly

the X-48B Blended Wing Body aircraft, was modified to evaluate the low speed stability and

control of a low noise version of a notional, future Hybrid Wing Body (HWB) aircraft design.

The HWB design stems from concept studies being conducted by NASA's Environmentally

Responsible Aviation project of future potential aircraft designs 20 years from now.

"Working closely with NASA, we have been privileged throughout X-48 flight-testing to

explore and validate what we believe is a significant breakthrough in the science of flight and

it has been a tremendous success for Boeing," added Bob Liebeck, a Boeing Senior Technical

Fellow and the company's BWB program manager. (Boeing, 2013)

While NASA believes a BWB design could be seen in future passenger aircraft 20 years from

now, Boeing has its eyes on military applications such as aerial refuelling and cargo missions.

Both Boeing and NASA plan to continue to develop BWB technology with Boeing hoping to

develop of a larger-scale, transonic BWB demonstrator in the future.

-- 12 --

8. REFERENCE

Boeing. (2013). Frontier. Boeing.

Dunbar, B. (2007, 11 08). NASA. Retrieved 04 01, 2014, from Time Magazine Recognizes

the X-48B: http://www.nasa.gov/vision/earth/improvingflight/bwb-timemagazine.html#.Uz-

7svmSwk1

Dunbar, B. (2010, 02 11). NASA. Retrieved 04 01, 2014, from NASA Dryden Past Projects:

X-48B Blended Wing Body: http://www.nasa.gov/centers/dryden/research/X-

48B/#.U0A1PvmSwk3

Elton, J. (2007, 08 10). Treehugger. Retrieved 04 01, 2014, from X-48B Blended Wing

Body Research Aircraft Has Lift-Off: http://www.treehugger.com/cars/x-48b-blended-wing-

body-research-aircraft-has-lift-off.html

Gibbs, Y. (2014, 02 28). NASA. Retrieved 04 01, 2014, from NASA Armstrong Fact Sheet:

X-48 Hybrid / Blended Wing Body:

http://www.nasa.gov/centers/armstrong/news/FactSheets/FS-090-DFRC.html#.Uz-

7s_mSwk2

Koehler, T. (2013, 04 12). Barrons. Retrieved 04 01, 2014, from Boeing X-48C Blended

Wing Body Research Aircraft Completes Flight Testing:

http://online.barrons.com/article/PR-CO-20130412-907394.html

NASA. (2012, 11 09). phys. Retrieved 04 01, 2014, from X-48 Blended Wing Body

research aircraft makes 100th test flight: http://phys.org/news/2012-11-x-blended-wing-

body-aircraft.html

Quick, D. (2013, 04 15). Gizmag. Retrieved 04 01, 2014, from X-48C Blended Wing Body

aircraft flight testing campaign comes to a close: http://www.gizmag.com/x-48c-blended-

wing-body-campaign-completed/27066/

Smith, R. (2007, 07 31). Symscape. Retrieved 04 01, 2014, from Blended Wing-Bodies and

Flying Wings: http://www.symscape.com/blog/blended-wing-bodies-flying-wings