X-48 Blended Wing Body (BWB)
Boeing Phantom Works has studied a number of 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.
X-48A Blended Wing Body-Low-Speed Vehicle
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 precompetitive 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 intercenter 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.
X-48A BWB-LSV Description
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.
X-48A Flight Test Program
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 included 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 would 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 would 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 were designed to ensure safe flight operations.
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. The LSV Program encountered major problems as flight control system development had to beput on hold when commitments to other programs changed the Agency’s priorities and resourceallotments.
The X-48B is a smaller eight-and-a-half percent scale prototype. The X-48B prototypes were 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 would 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.
The X-48B aircraft flew 92 times at NASA Dryden between 2007 and 2010.
The Boeing X-48C research aircraft flew for the 30th and final time 09 April 2013, marking the successful completion of an eight-month flight-test program to explore and further validate the aerodynamic characteristics of the Blended Wing Body design concept. All 30 flights were conducted at NASA's Dryden Flight Research Center. The X-48C typically flew for approximately 30 minutes on most flights, reaching speeds of up to 140 miles per hour and attaining an altitude of about 10,000 feet. X-48C flight testing began Aug. 7, 2012.
Primary changes to the X-48C model from the B model were geared to transforming it to an airframe noise-shielding configuration. The X-48C retained most dimensions of the B model, with a wingspan slightly longer than 20 feet and a weight of about 500 pounds. The X-48C is configured with two 89-pound thrust turbojet engines, instead of three 50-pound thrust engines on the B-model. In addition, the wingtip winglets were relocated inboard next to the engines on the C-model and the aft deck was extended about 2 feet at the rear. Because handling qualities of the X-48C were different from those of the X-48B, the project team modified the flight control system software, including flight control limiters to keep the airplane flying within a safe flight envelope. This enabled a stronger and safer prototype flight control system suitable for future full-scale commercial hybrid or blended wing aircraft
The X-48C, designed by Boeing Research & Technology, built by Cranfield Aerospace Ltd., and flown in partnership with NASA and the U.S. Air Force Research Laboratory, is a scale model of a heavy-lift, subsonic vehicle that forgoes the conventional tube-and-wing airplane design in favor of a triangular tailless aircraft that effectively merges the vehicle's wing and body. Boeing believed the concept could be developed in the next 15 to 20 years for military applications such as aerial refueling and cargo missions.
|Join the GlobalSecurity.org mailing list|