Birds are more efficient when they fold their winds during the upstroke, according to a study published in the journal Advanced Intelligent Systems. A team of researchers from Lund University, Sweden, believes that copying this wing-folding behaviour is going to help developing flapping drones.
Even now extinct bird-like dinosaurs benefited from folding their winds during upstroke as they developed active flight. Among flying animals alive today, birds are undoubtedly the most efficient, making them the perfect source of inspiration for the development of drones.
To determine which flapping strategy is best, a Swedish-Swiss research team built a robotic wing that mimics how different birds fly. “We have built a robot wing that can flap more like a bird than previous robots but also flap in a way that birds cannot do. By measuring the performance of the wing in our wind tunnel, we have studied how different ways of achieving the wing upstroke affect force and energy in flight”, said Christoffer Johansson, biology researcher at Lund University.
Researchers know that birds flap their wings more horizontally when flying slowly. It seems like birds do it like that — even though it requires more energy — because it’s easier to create enough force to stay up and propel themselves. The team believes this is one aspect of flying that drones should copy to increase the range of speeds and conditions they can fly.
“The new robotic wing can be used to answer questions about bird flight that would be impossible simply by observing flying birds. Research into the flight ability of living birds is limited to the flapping movement that the bird actually uses”, explained Johansson.
This work explains why birds flap their wings the way they do by finding out which movements are the most efficient and create the most force. The authors defend that these results can be used in other research areas, such as understanding how migratory birds are affected by the weather. When it comes to drones, there are also many potential applications in the future, including developing drones to deliver goods to inaccessible areas. “How the wings move is of great importance for performance, so this is where our research could come in handy,” concluded Johansson.
Ajanic E, Paolini A, Coster C, Floreano D Johansson C (2023) Robotic Avian Wing Explains Aerodynamic Advantages of Wing Folding and Stroke Tilting in Flapping Flight. Advanced Intelligent Systems, https://doi.org/10.1002/aisy.202200148