THE 456th FIGHTER INTERCEPTOR SQUADRON

HAMPTON, Va., May 04, 2006 -- In cooperation with NASA and the U.S. Air Force Research Laboratory, the Phantom Works organization of Boeing [NYSE: BA] is taking another step toward exploring and validating the structural, aerodynamic and operational advantages of a futuristic aircraft design called the blended wing body, or BWB.

Two high-fidelity, 21-foot wingspan prototypes of the BWB concept have been designed and produced for wind tunnel and flight testing this year. The Air Force has designated the vehicles as the "X-48B," based on its interest in the design's potential as a flexible, long-range, high-capacity military aircraft.

X-48B Ship No. 1 began wind tunnel testing on April 7 at the Langley Full-Scale Tunnel at NASA's Langley Research Center. When testing is completed in early May, it will be shipped to NASA's Dryden Flight Research Center in California to serve as a backup to Ship No. 2, which will be used for flight testing later this year. According to the team, both phases of testing are focused on learning more about the low-speed flight-control characteristics of the BWB concept.

"The X-48B prototypes have been dynamically scaled to represent a much larger aircraft and are being used to demonstrate that a BWB is as controllable and safe during takeoff, approach and landing as a conventional military transport airplane," said Norm Princen, Boeing Phantom Works chief engineer for the X-48B program.

The X-48B cooperative agreement by Boeing, NASA and the Air Force Research Laboratory (AFRL) culminates years of BWB research by NASA and Boeing. AFRL is interested in the concept for its potential future military applications.

"We believe the BWB concept has the potential to cost effectively fill many roles required by the Air Force, such as tanking, weapons carriage, and command and control," said Capt. Scott Bjorge, AFRL X-48B program manager. "This research is a great cooperative effort, and a major step in the development of the BWB. AFRL is inspired to be involved in this critical test program."

NASA also is committed to advancing the BWB concept. NASA and its partners have tested six different blended wing body models of various sizes over the last decade in four wind tunnels at the Langley Research Center.

"One big difference between this airplane and the traditional tube and wing aircraft is that -- instead of a conventional tail -- the blended wing body relies solely on multiple control surfaces on the wing for stability and control," said Dan Vicroy, NASA senior research engineer at the Langley Research Center. "What we want to do with this wind-tunnel test is to look at how these surfaces can be best used to maneuver the aircraft."

The two X-48B prototypes were built for Boeing Phantom Works by Cranfield Aerospace Ltd., in the United Kingdom in accordance with Boeing requirements and specifications. Made primarily of advanced lightweight composite materials, the prototypes weigh about 400 pounds each. Powered by three turbojet engines, they will be capable of flying up to 120 knots and 10,000 feet in altitude during flight testing.

Boeing also contracted with Cranfield Aerospace to provide the ground-control station, in which a pilot will remotely control the X-48B during flight research testing.

As part of Boeing's long-range business strategy, its Phantom Works advanced research and development organization defines and develops innovative technologies and systems such as the blended wing body concept to meet future aerospace needs.

A futuristic "blended wing" plane developed by NASA has passed crucial wind-tunnel tests. These reveal that engineers may have overcome some of the controllability challenges associated with the revolutionary aircraft design.

Designs for blended wing planes are a dramatic leap from that of today's passenger jets – instead having a tube-like fuselage. They look more like paper aeroplanes with engines mounted on top and at the rear.

The unusual shape is much more aerodynamic than a normal plane, which means it could use 20% less fuel. And it should also be much quieter for people on the ground because the engines sit on top of its wings instead of hanging below.

But the extremely sleek design means doing away with a tail – a crucial control element – so engineers have had to come up with other ways to make the aircraft pitch, yaw and roll. For a blended wing plane, this means relying on curved flaps along the edge of each wing and rudders on each wingtip.

NASA engineers have struggled to find the perfect configuration for the design but the latest tests suggest they are getting closer. They took a 5% scale model of their latest blended wing design to a wind tunnel at Langley Research Center in Hampton, Virginia, US, for a free-flying test.

"We were kind of concerned early on that it was going to be difficult to fly,” says Dan Vicroy, head of the project at NASA. "The bottom line from the test: this particular configuration flew great."

The engineers were particularly keen to see what would happen when the aircraft approached maximum lift and then lift suddenly dropped, as can happen when an aircraft hits turbulence. Unlike previous designs, the aircraft did not start to roll or pitch backwards.

During wind tunnel tests, a model is normally mounted while wind flows around it, allowing engineers to measure forces on the static design. This time, however, three "pilots" remotely controlled the scale model's movement during the test. It was the first time anyone has tried such a test of a blended wing design.

The other design challenge presented by a blended wing body is structural. A tube-shaped fuselage is easy to keep pressurized because pressure is distributed evenly inside. When you squash the tube down into such an irregular shape, it places more stress on the structure. NASA researchers hope to combat this by using composite structures and by adding pillars inside to add strength.

NASA has been researching the flying wing design since the early 1990s and has tested concepts with McDonnell-Douglas, which was taken over by Boeing in 1998. Next summer, Boeing and Cranfield University in the UK will test another blended wing design, the X-48B, at Dryden Flight Research Center in California, US.

Aircraft companies, such as Boeing, have discussed using such an aircraft for both commercial and military purposes. If a company were to start building a blended wing body aircraft today, it could hit the market in about seven years.

^{Graham Warwick
in Cranfield, UK}

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Suspended from a yellow frame, the manta-like shape shakes almost imperceptibly as the second X-48B demonstrator undergoes final testing before being shipped to Edwards AFB in California. The ground vibration testing is being conducted by Cranfield Aerospace, which has built the blended wing-body (BWB) unmanned research vehicle for Boeing’s Phantom Works in an unusual example of transatlantic cooperation.

“We are providing Boeing with a research tool in which to test their flight control system software,” says D J Dyer, Cranfield Aerospace’s general manager UAV systems. The X-48B will allow the BWB’s low-speed characteristics and complex control system to be explored in flight. “We are giving them the complete thing – two 8.5%-scale aircraft, a ground control station, support equipment and spares,” says Prof Ian Poll, business development director.

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^{NASA and the US Air Force Research
Laboratory are backing the X-48B project}

Boeing, which has worked on BWB design for several years, planned to build a larger 14%-scale demonstrator, the X-48A, but NASA budget cuts killed the project. “Boeing decided we still needed to demonstrate the flight controls, so we looked for people to work with,” says Phantom Works’ X-48B chief engineer Norm Princen. “We did not want to build the vehicle in-house, so we chose Cranfield.”

Designing and building two X-48B BWB low-speed vehicles (LSV) fits with Cranfield Aerospace’s “concept to flight” strategy to reduce the cost and time to obtain high-quality aerodynamic and flight control data by combining its rapid prototyping and unmanned aircraft capabilities. “It is enabled by UAV technology and is a new way to look at aircraft design,” says Poll. “If you can get good data in the early stages of a programme you can reduce the risk enormously. BWB is right at the very beginning, and Boeing can get very high-quality data by flying this vehicle,” he says.

Formed in 1997 as a wholly owned subsidiary of Cranfield University, and located north of London, the company holds civil and military approvals to design, build and fly manned and unmanned aircraft. “We are a for-profit company, and all of our income is from commercial contracts,” says Poll. The company has access to the university’s intellectual and physical property, and the majority of its almost 100 employees are ex-university, but it gets no academic funding. “We only survive if we win contracts and make a profit,” says managing director David Gardner.

Dynamic Scaling

Design of the 6.2m (20.4ft)-span, 9.3m² (100.5ft²)-area X-48B was a challenge because it is scaled dynamically, rather than simply geometrically. Although much quicker than those of the full-size aircraft, the vehicle’s responses will scale perfectly, says Poll. “The moments of inertia are scaled, which is not normal. The frequency of the short-period oscillation, for example, will not be the same as full-size, but will be a function of the scaling parameter.”

Cranfield designed the X-48B with CATIA software, using the outer mould line of Boeing’s 451L BWB study configuration, for which an extensive wind tunnel database has been developed. Dynamic scaling put a premium on weight saving and mass distribution, and the vehicle has a carbonfibre airframe built by UK subcontractor Lola Composites. “As you move away from the centre of gravity, mass is much lower than normal, and in places the skin is just one laminate thick,” says Dyer. “There was an enormous amount of finite-element modeling work done by Boeing with Cranfield.”

Funding the X-48B from its own resources, Boeing went to a smaller scale than the X-48A so it could afford two vehicles and a more robust test programme, says Princen. The smaller size also allowed Cranfield to tap into the model aircraft market, which supplied the X-48B’s three 50lb-thrust (0.22kN) micro-jet engines. These give the 178kg (392lb) vehicle a maximum airspeed of 118kt (218km/h), altitude of 10,000ft (3,000m), endurance of 60min and range of 218km (118nm).

The flying-wing vehicle has 20 control surfaces along its trailing edge, each driven by one or two electric actuators supplied by Kearfott and originally developed for the AAI Shadow tactical UAV.

Cranfield built the avionics system, which includes dual single-board processors – one for housekeeping and one for flight control, into which Boeing can upload its software. Cranfield is not allowed access to the flight control software because of US export restrictions.

“All the flight control software development is done by Phantom Works. The air vehicle is test equipment for flight control system research,” says Princen. “The big research challenge is control allocation.” The BWB’s control responses are non-linear and highly coupled, so all 20 surfaces are active all the time. Roll produces adverse yaw, so in addition to winglet rudders, the outer pairs of ailerons are split to act as drag rudders as well as speed brakes.

Remotely Piloted

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^{The first X-48B completed 250h testing
in NASA windtunnel}

Cranfield has also supplied a ground control caravan with pilot and flight-test engineer stations. The X-48B is remotely piloted, and will be flown by a Boeing test pilot using conventional stick and throttle and an out-the-window image down linked from a camera in the vehicle’s nose and overlaid with a head up display. Normally the aircraft will take off from and land on the Edwards lakebed, but there is a recovery parachute and landing airbag for emergencies. There is also a spin recovery parachute in case the aircraft departs controlled flight during high-alpha stall testing.

Flying experience with the BWB configuration is limited to a 5.5m-span propeller-driven model built by Stanford University and flown in 1997, and tethered wind tunnel tests of a NASA 3.7m-span free-flight model last year. Data from the Stanford flights was not good quality, says Princen, but the NASA tests proved useful. The X-48B will investigate stall characteristics, spin and tumble, asymmetric thrust and ground effects, plus dynamic interactions between the control surfaces, wing aerodynamics and inlet conditions that cannot be tested in a windtunnel.

The first X-48B has just completed wind tunnel testing at NASA Langley in Virginia and will be used as back-up for the second vehicle, now en route to NASA Dryden at Edwards for flight testing. Complete except for its fuel system, the first vehicle underwent 250h of wind tunnel testing to measure air loads and hinge moments. The flight control system was used to record air data during, and reposition control surfaces between, runs and resulted in “very efficient” testing, says Princen – “250h versus 1,000-2,000h without movable controls”.

Testing at Edwards will begin with low-risk parameter identification flights and work up to high-risk, high-alpha flying. The X-48B will fly first with fixed extended leading-edge slats. These will then be replaced with fixed retracted slats and the tests repeated, an approach Princen says is simpler. As the X-48B will assess the BWB’s behavior at high angles of attack and speeds close to the stall, there is a risk of the aircraft spinning or tumbling end over end. Poll points out the irony in the tests being conducted at Edwards, named after a US Air Force test pilot killed in 1948 when his Northrop YB-49 flying-wing bomber began to tumble.

Although the X-48B will respond much more quickly than the full-scale vehicle, Boeing will be able to scale up the data for use in its BWB flight simulator. The control laws designed by the Phantom Works are intended to provide the control responses of a conventional aircraft, despite the BWB’s unconventional flying characteristics. “We don’t want to have to retrain the pilot to fly the vehicle. It should fly like a 777 or a C-17,” says Princen.

Boeing Phantom Works has studied Blended Wing Body (BWB) aircraft concepts. In a continuing effort to study the flight characteristics of the BWB design, a 17-foot wingspan, remote controlled model has been successfully flown. The X-48, a 35-foot model, was built at NASA 'a Langley Research Center. Test flights of this scale, 1,800-pound model are scheduled to begin in 2004.

The Blended Wing Body offers greater structural, aerodynamic and operating efficiencies than today 's more conventional tube-and -wing design. Its modular design also allows for center body growth while maintaining common wings. These features translate into greater range, fuel economy, reliability and life cycle savings, as well as lower manufacturing costs. They also allow for a wide variety of potential military and commercial applications.

The Blended Wing Body (BWB) is a hybrid shape that mainly resembles a flying wing, but also incorporates some features of a conventional airliner. The futuristic airframe is a unique merger of efficient high-lift wings and a wide airfoil-shaped body, causing the entire aircraft to generate lift and minimize drag, thereby increasing fuel economy. Passenger and cargo areas are located within the center body portion of the aircraft.

NASA and industry studies suggest that a large commercial BWB aircraft could be developed to carry 800 or more passengers; however, recent studies have focused on vehicles in the 450-passenger class. Because of its efficient configuration, the BWB would consume 20 percent less fuel than jetliners of today, while cruising at high subsonic speeds on flights of up to 7,000 nautical miles. An aircraft of this type would have a wing span slightly wider than a Boeing 747 and could operate from existing airport terminals.

One potential application is a BWB tanker for performing multi-point refueling. Equipped with three smart booms, two hose/drogue refueling points and automated refueling capabilities. A BWB tanker would be able to accommodate simultaneous air-to-air refueling of multiple conventional aircraft or UAVs. And because fuel would be 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 signature. These capabilities make the BWB suitable as a long-range standoff weapons platform as well. And should the market ever warrant a larger commercial airplane, the BWB could be designed to accommodate up to 800 passengers or more.

Problems in the development of the flight control system as well as changing priorities at NASA led to the termination of the X-48A program.

In 1997, Darrel R. Tenney, Director of the Airframe Systems Program Office, initiated a series of in-house team studies to determine if Langley could support the fabrication and development of a series of unmanned, remotely controlled air vehicles that could be flown to support Langley’s interest in revolutionary configurations. Langley’s Director, Jeremiah F. Creedon, strongly supported the studies. At the same time, Joseph R. Chambers’ staff in the Aeronautics Systems Analysis Division proposed a related new program based on the selection of pre-competitive advanced configurations that would be designed, evaluated, fabricated, and test flown using remotely piloted vehicle technology at Dryden. The program, known as Revolutionary Concepts for Aeronautics (RevCon), would be based on a 4-year life cycle of support for concepts selected. Initial reactions to the proposed program from NASA Headquarters and Dryden were favorable, and following interceptor discussions, a formal RevCon Program was initiated in 2000, which was led by Dryden. Following a review of other advanced vehicle concepts by an intercenter team, the team selected the BWB as one of the concepts for further studies.

NASA was developing a 35-foot wing span, remotely-piloted research aircraft based on the BWB design. The vehicle is called the Blended Wing Body-Low-Speed Vehicle (BWB-LSV). The primary goals of the test and research project are to study the flight and handling characteristics of the BWB design, match the vehicle's performance with engineering predictions based on computer and wind tunnel studies, develop and evaluate digital flight control algorithms, and assess the integration of the propulsion system to the airframe.

The Blended Wing Body research project is a partnership between NASA's Aerospace Vehicle Systems Technology Program and the Boeing Company. Funding and workforce for the project came from both sources. In addition, the Flight Research Base Program at Dryden Flight Research Center, Edwards, Calif., and Old Dominion University, Norfolk, Va., are partners in the testing phase of this project.

During the late 1990s, wind tunnel and free-flight tests have been conducted to study certain aerodynamic characteristics of the BWB design. At the NASA Langley Research Center in Hampton, Va., researchers tested three wind tunnel models of the BWB-LSV to evaluate the design's stability and control and spin/tumble characteristics. Data obtained during these tests were used to develop flight control laws and helped to define the flight research program. The researchers will incorporate all of the wind-tunnel (and later flight) data into simulations of the BWB-LSV and a full-scale BWB to evaluate the plane's flying characteristics.

The BWB-LSV is a 14%-scale version of the 450-passenger study aircraft. Built primarily of composite materials and weighing about 2,500 lb., the platform features a wide arrowhead-like body that blends into tapered wings swept aft. Flight control surfaces, or elevons, span the trailing edges of the wings while the rudders are located in winglets on each wing tip.

Three 240-lb thrust turbojet engines, from Williams International Corporation, Walled Lake, Mich., were mounted on low aerodynamic pylons across the rear portion of the center body. All three engines will operate from a single fuel tank located near the vehicle's center of gravity. The maximum speed of the BWB-LSV would be about 165 mph.

Electric actuators in the flight control system link the exterior control surfaces with a central digital fly-by-wire flight control computer carried in the center body of the aircraft. The aircraft was to be flown by a NASA research pilot sitting at a cockpit station in the remotely piloted vehicle (RPV) facility at the NASA Dryden Flight Research Center. Instruments and displays in the RPV cockpit will provide the pilot with the same systems and performance data commonly displayed in conventional research aircraft cockpits.

Two small video cameras was be installed on the BWB-LSV. One, behind the mock cockpit windscreen, presents a forward-looking view on a large video screen in the RPV cockpit station. The NASA project pilot will use this view, along with the cockpit instrument array, to fly the vehicle. The second camera was mounted atop the rearward portion of the center body, to view external areas of the vehicle during flight.

Numerous sensors installed throughout the vehicle measure aerodynamic loads, air pressures, temperatures, engine performance, and other important test and research parameters during each flight. Data would be automatically transmitted to the Dryden mission control center and monitored during flight by project engineers and other members of the test team.

A spin recovery system built into the test aircraft would allow the vehicle to be flown to its maximum angle of attack and as slow as its stall speed. The system will be used to deploy a parachute if the vehicle begins an uncontrollable descent, such as an unrecoverable spin. The parachute attach line would be cut, separating the vehicle from the canopy as soon as stabilized flight could be resumed.

Construction of the BWB-LSV began in early 2000 and was scheduled for completion in late 2002. Integration and ground testing of the vehicle was to continue through 2003, followed by the test flight program. When assembly of the BWB-LSV was completed at the Langley Research Center, it was to undergo three months of wind tunnel testing at the Old Dominion University (ODU) Full-Scale Wind Tunnel Facility in Hampton, Va.

Research in ODU's massive 30 by 60-foot wind tunnel wwould include operating the engines and the external flight control surfaces at various air speeds. Data from this research will give engineers and designers a better understanding of the aerodynamics associated with the BWB's unique design prior to flight, as well as a unique opportunity to test the same vehicle on the ground and in flight.

In a joint effort between NASA and Boeing, in June 2004 the flying wing aircraft design began preliminary testing in a high-pressure, super-cold wind tunnel at NASA Langley. The tunnel -- the National Transonic Facility -- accurately tests scale models at speeds and conditions simulating actual flight.

At the conclusion of the wind tunnel research the Low-Speed Vehicle was to be transferred to Dryden where it will be readied for its first flight, scheduled [as of 2001] to take place in 2004.

Preflight work at Dryden will include final systems integration, ground vibration tests to investigate the design's structural modes, and electromagnetic tests to assure that it can be remotely operated without causing electronic interference to aircraft systems. The aircraft will undergo a final combined systems test and taxi testing prior to the actual flight research.

The flight schedule called for approximately 30 to 50 one-hour flights over a period of a year. Like most flight test and research programs, the schedule begins with benign operations and increases in complexity as flight experience is gained.

All flying of the remotely piloted vehicle wwould be in restricted airspace over the Dryden complex at altitudes up to 10,000 ft.

The flight tests was to use two sets of flight control laws. One is a basic set that will be used for most of the research flying, developed jointly by Langley and Dryden. The other set of flight control laws will help investigate specific research and high-risk test points. If the reaction of the vehicle is unacceptable during a high-risk flight, control of the vehicle will revert to the basic set of control laws. These procedures are designed to ensure safe flight operations.

The X-48B is a smaller eight-and-a-half percent scale prototype. The X-48B prototypes have been dynamically scaled to represent a much larger aircraft and are being used to demonstrate that a blended wing body is as controllable and safe during takeoff, approach, and landing as a conventional military transport airplane. Initially it was tested in the Langley Full-Scale Tunnel at NASA's Langley Research Center in Hampton, VA. Boeing Phantom Works' advanced research and development unit partnered with NASA and the U.S. Air Force Research Laboratory (AFRL) at Wright Patterson Air Force Base, Ohio, to explore and confirm the structural, aerodynamic and operational advantages of the blended wing body design.

The team produced two high-tech prototypes of the BWB, built to Boeing specifications by Cranfield Aerospace in England, for wind tunnel and flight-testing. The Air Force designated the vehicles as the "X-48B" based on its interest in the design's potential as a multi-role, long-range, high-capacity military aircraft. X-48B Ship No. 1 is the wind tunnel test model. In mid-May 2006, the research team successfully completed 250 hours of wind tunnel tests on the X-48B Ship No. 1, at the historic Langley Full Scale Wind Tunnel at NASA’s Langley Research Center, Langley Air Force Base, Va. The prototype was then shipped to NASA’s Dryden Flight Research Center at Edwards Air Force Base, Calif., where it would serve as a backup to Ship No. 2, which will be used for planned remotely piloted flight tests at Edwards. Ship No. 2 had been scheduled to be used in remotely-piloted flight testing at Dryden.

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Boeing and NASA will flight test the X-48B, a 6.4m (21ft)-span, 8.5% scale model of a blended wing body (BWB) configuration, next year at the US space agency’s Dryden Flight Research Center in California.

The remote-controlled vehicle will be powered by three turbojets and will test flight-control laws. Boeing is developing the BWB in co-operation with the US Air Force Research Laboratory as a multi-role military aircraft.

The flight testing will follow statically mounted wind tunnel tests of a second 8.5% model in NASA Langley Research Center’s full-scale tunnel next February, focusing on aerodynamic forces and moments. “Cranfield Aerospace in the UK is building the two vehicles. They should be finished in the next month or so,” says Langley’s flight dynamics principal investigator, Dan Vicroy.

Tethered free-flight tests of a 3.66m-span, 5%-scale X-48B model in the full-scale tunnel were performed in September. Vicroy says such tests are rare and were last performed eight years ago.

Simulated airspeeds were low and the vehicle’s maximum stall angle was investigated. The February tests will also examine the BWB’s departure characteristics.

Researchers were “pleasantly surprised” by how well the model flew. Vicroy says the vehicle did not have a natural tendency to “pitch back” in the stall and expected pitch problems did not materialize.

NASA could have used complex control laws developed by Boeing, but found its own simpler laws worked with the BWB’s trailing-edge control surfaces. The 5% scale model was made of a carbonfibre composite to ensure the weight and inertia characteristics in roll, yaw and pitch accurately modeled those of a full-sized BWB

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	Boeing’s experimental X-48B plane prepared for testing. The unmanned, blended-wing aircraft recently flew for the first time, reaching an altitude of 7,500ft (2,300m). The innovative design is quieter and more fuel efficient than conventional aircraft.

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