Blended Wing UAV
Unique unmanned craft’s robust composite design a plus for rough duty.
By Sara Black, Technical Editor | May 2007
The booming unmanned aerial vehicle (UAV) market continues to expand with hundreds of designs competing for military and civilian contract dollars worldwide. While UAV wingspans range from commercial airliner size down to palm-sized micro flyers, small long-endurance “tactical” UAVs, those that support intelligence, surveillance and reconnaissance (ISR), are becoming key components of military and homeland security missions. One of the more innovative tactical UAVs on the market is the compact (10-ft/3m wingspan) “blended wing” Killer Bee Unmanned Aircraft (KB-UA) produced by Swift Engineering Inc. (San Clemente, Calif.).
Swift, founded in 1983, is well known among automotive enthusiasts for its winning open-wheel race car chassis designs and composite components. But, says Larry Reding, Swift’s Killer Bee program manager, the company wanted to diversify. “Our car-racing legacy and staff skills gave us solid experience that we were able to apply to other markets.”
Mark Page, the company’s chief scientist and aerospace designer, together with aerospace engineer Matt McCue, developed the KB-UA. The current model, KB-UA-4, builds on previous experimental prototypes that first flew in 2003. Although a marketing partner relationship with Northrop Grumman Corp. (El Segundo, Calif.) ended several months ago, Swift continues to develop the KB-UA-4, says Page. “We’ve developed an inexpensive way to make a rugged UAV, and we think there’s a market for it.”
Fusing the fuselage with the wings
Page, who once worked at NASA and is the company’s expert on blended wing concepts, claims that Swift was the first to develop a blended wing UAV, which is similar to but subtly different from the “flying wing,” a design that has existed since the early days of aviation. A flying wing has no separate fuselage and is made up only of wing structure. Several flying wing variants have flown successfully, including Nazi Germany’s Horten Ho-229, Northrop’s YB-49 and probably the best-known example, the B-2 Spirit bomber developed by Northrop Grumman in the late 1980s. The KB-UA differs in that it has a distinct fuselage, which is flattened to form an aerodynamic airfoil. Its aft-swept wings merge smoothly with the fuselage body to form a tail-less, arrowhead-like shape with slender, downturned outer wings. NASA is considering a similar blended wing design for future large cargo aircraft (see photo at right). While flight stability can be tricky minus a traditional tail, with its moveable control surfaces, Swift has addressed this by incorporating movable flaps at the back of the craft’s outer wings, whose droop assists in yaw stability.
Swift adopted the concept for the KB-UA for several reasons. First, merging the wings and fuselage into a single airfoil significantly reduces aerodynamic drag, improving fuel economy. Second, KB-UA is considered a “thick” airfoil when compared to traditional thin-skinned, fragile flat wings, says McCue, giving it better structural efficiency: “The aircraft’s thicker airfoil and triangular shape means less material is needed to achieve required airframe stiffness as compared to a traditional rib-and-spar wing design, which saves material and manufacturing cost,” he explains. It makes the craft inherently rugged and much less susceptible to damage.
McCue also notes that the design maximizes the aircraft’s volume-to-wingspan ratio, allowing a disproportionately large payload capacity — comparable to UAVs with a 30 to 50 percent larger wingspan — in a compact package. For example, the ScanEagle UAV, built by The Insitu Group (Bingen, Wash.) in partnership with The Boeing Co., Seattle, Wash. (see end note), is a small, traditional tube-and-wing design now in military service with a 10 ft/3m wingspan that carries about 7 lb/3 kg of equipment in combat missions. By contrast, he says, the KB-UA, with the same wingspan, has a 30-lb/14-kg payload capacity. Design for rough duty
