According to a recent study by Lund University in Sweden, birds fly more efficiently by folding their wings as they rise. The results could mean that folding wings is the next step in improving the propulsion and aerodynamic efficiency of flapping drones.

Even the ancestors of birds – extinct bird-like dinosaurs – benefited from folding their wings as they moved upward while developing active flight. Of all currently living flying animals, birds are the largest and most prolific. This makes them particularly interesting as an inspiration for drone development. However, determining which flapping strategy is best requires aerodynamic studies of different flapping modes. A Swedish-Swiss research team has designed a robotic wing that can do just that; flapping wings like a bird and more.

“We’ve created a robot wing that can flap more like a bird than previous robots, but can also flap in a way that birds can’t. By measuring the performance of the wing in our wind tunnel,” said Lund University biologist Kristoffer Johansson. “We looked at how it affects energy,” he says.

Previous studies have shown that birds flap their wings more horizontally when flying slowly. A new study shows that birds probably do this even if it requires more energy, because it’s easier to generate forces large enough to stay in the air and move. This is something drones can emulate to increase the speed range they can fly.

“The new robotic wing can be used to answer questions about bird flight that are not possible by simply observing birds in flight. Research on the ability of living birds to fly is limited to the flapping motion actually used by the bird,” explains Kristoffer Johansson.

The research explains why birds flap their wings in this way by finding which movement patterns generate the most force and are most efficient. The results can also be used in other research areas, such as to better understand how climate change affects bird migration and access to food. There are also many potential applications for drones where this knowledge could be put to good use. A field can use drones to deliver goods.

“Unmanned aerial vehicles can be used for delivery, but they must be efficient enough and able to handle the extra weight. How the wings move has a huge impact on performance, so our research could be useful,” says Kristoffer Johansson.