Over the last 100 million years, birds have been developing winged flight technology to a degree that has been extraordinarily difficult, if not impossible, for humans to replicate. Feathered wings on a bird essentially do two things – create lift and create drag. A bird needs lift for flight, but once in the air drag becomes an issue, especially in strong headwinds. Over the millennia, birds have found a creative solution to problem.
Birds’ wings have three key features – overlapping feathers, a joint at the end of the wing, and the ability to morph (change shape) in flight for more maneuverability, or more speed. By retracting their primary feathers, birds can create less surface area on the wings, thus increasing speed and decreasing maneuverability and drag. When the primary feathers extended, surface area increases along with drag turning radius, but at the expense of slower speed.
Until now, no one has been able to produce a mechanical function of birds’ wings with any real accuracy. However, engineers at École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland, think they have found a solution to this problem. They have developed a mini drone with artificial, feathered wings that can fold allowing the drone to maneuver like a real bird. In testing of their prototype, EPFL engineers found that they could vary the drone’s folding wings up to 41 percent, causing lift to decrease by 32 percent and drag to decrease by 40 percent. The drone was able to increase its top speed from 6.3 meters per second to 7.6 meters per second with the wings fully retracted. However, by decreasing the surface area of the wings, maneuverability was compromised and the drone’s turning radius increased from 3.9 meters to 6.6 meters.
Along with issues of maneuverability and drag comes the issue of roll control. For typical fixed-wing drones roll control is established using little flaps, known as ailerons, attached to the back edge of the wings. This becomes impossible, however, with feathered wings. Instead, the EPFL engineers had their drone mimic the mechanics of actual birds and use asymmetric folding of the wings, meaning one wing retracted while the other stayed extended. The engineers discovered that asymmetric folding wings worked just as well, if not better, than ailerons especially in sharp-turn situations.
The use cases for this type of evolution in drone technology are numerous. One such example is to integrate EPFL’s folding wing technology into the ICARUS program in development at DARPA which I discussed in a previous post. This would greatly assist DARPA’s micro air vehicles with their precise, gentle airdrops of critical supplies in the field. We could even see an evolution in the sport of drone racing as folding wing technology is adopted by the pilots of those vehicles looking to race on more complex courses. A more far-reaching scenario for this technology at scale could see soldiers replace parachutes with folding-wing systems, allowing for more accurate and graceful jumps from aerial platforms.
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