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Issue link: https://insideunmanned.epubxp.com/i/643419
38 unmanned systems inside January/February 2016 AIR RESEARCH UK-based Blue Bear Systems Research is one UAS frm turning to birds for inspiration. A few years ago, the company worked with the University of Oxford's zoology department to develop and fight test iMorph, a small UAS with bio-inspired wings that change span and area like a bird's, Blue Bear Product Engineer Mike Snook said. The team wanted to grasp exactly what advantages the large area and aspect ratio changes in a bird's wing bring to fight, Snook said. It took about four months to get from concept to frst take off, and the project took six months to complete. "There are a lot of times you see birds fying when UAS can't because it's too windy. We wanted to understand what birds do that is so much better than existing fxed-wing aircrafts," Snook said. "We wanted to understand how this could be applied to improve our current technology." THE BENEFITS A bird's wing works in two modes— extended and tucked—and the team saw effciency gains in both when compared to a fxed-wing UAS, Snook said. With wings extended, iMorph is easy to hand launch and has an effcient, stable loiter. It also can land slowly. With wings tucked, this UAS displays better agility than a fxed-wing aircraft and greater effciency both at higher speeds and in windy conditions. While Snook said effciency is the biggest advantage, he's sure there are many other benefts to developing drones inspired by nature. "There are quite a few uses we don't even know about yet," Snook said. "It's one of those things you have to understand what it can do before you can apply it to a situation." THE CHALLENGES Developing a bird-inspired UAS is diffcult, and in this case Snook said the biggest challenge was the wings' large area change. The system's morphing wing structure features overlapping sections like bird feathers, and it was important to make sure they lined up and didn't fap about during fight. Creating the structure When fapping and fying on the down stroke, which is the wing's power stroke, the wings fully extended. During the up stroke the wings would bend and reduce the amount of negative lift. With this design we increased the ratio of positive lift to negative lift. " –Aimy Wissa, assistant professor in the Department of Mechanical Science and Engineering at the University of Illinois Urbana Champaign " Developing iMorph stream to where they started their foraging run, enabling them to start over and continue looking for food. This enables them to forage longer, Hedrick said. They're also good at working in groups and avoiding collisions—all things drones need to do. One of Wissa's projects, which was part of her PhD work, involved designing a joint that mimics the function of a bird's wrist. Birds use different gaits when cruising, taking off and landing, and different birds use different gaits. Wissa wanted to implement the gait kinematics a bird uses while cruising into a UAS design for enhanced energy efficiency. The team went to work and designed a pas- sive morphing wing system, Wissa said, mean- ing the wing would respond to external loads and change its shape naturally with no actuator telling it to go from point A to point B. "We put this compliant joint on a f lapping wing UAS," Wissa said, noting the University of Maryland and Penn State were also involved in this project. "When f lapping and f lying on the down stroke, which is the wing's power stroke, the wings fully extended. During the up stroke the wings would bend and reduce the amount of negative lift. With this design we increased the ratio of positive lift to negative lift." The overall benefit? The researchers im- proved power consumption by 50 percent and payload capability by 20 percent. Today, Wissa is working on two projects that focus on feathers, which all perform different functions. The first project looks at the covert feathers that provide the bird contour, she said. They cover about two-thirds of the wing and f lare out when deployed, enabling the bird to perform high angle maneuvers—maneuvers that current UAS can't achieve.