Flying insects like bees, dragonflies, and fruit flies can perform impressive aerodynamic feats, particularly when seeking to evade predators or the swatting motion of a human hand. Now Dutch scientists have built a flying robot capable of executing similar maneuvers—despite being much larger than the average insects—that could shed light on how these creatures achieve those feats. The scientists described their work in a new paper in Science.

There was a time when scientists believed that insect wings worked a lot like airplane wings. The up and down motion of their wings would generate lift because air flowing over the wing follows its slightly tilted surface, while the downward flow lowers the air pressure above the wing, lifting it just enough to keep the body aloft. (This is a simplified, and therefore incomplete, explanation for the complicated aerodynamics of airplane lift based on Bernoulli's principle, but it will suffice for the purposes of this post.) But in the 1990s, a zoologist named Charles Ellington decided to test this theory by putting various insects in actual wind tunnels. The conventional lift they measured simply wasn't sufficient to account for their ability to fly.

Ellington's subsequent research showed that a stable leading-edge vortex is the most likely explanation for how insects stay aloft. Once the vortex forms, it spirals out along the wing toward the tip, drawing air outward so as to avoid a stall. That explains how insects generate lift to hover, but not how they manage to execute complicated maneuvers like making rapid banked turns. That's possibly due to how an insect wing can rotate to slightly get rid of the vortex for an extra bit of lift, enabling the insect to change direction. But there is still plenty of mystery remaining for scientists to explore. And that's where this new flying robot comes in.

Matej Karasek of the Delft University of Technology in The Netherlands has long been intrigued by the agility of flying insects, using them as inspiration to develop tail-less flapping-wing robots. "The major challenge was to come up with a wing actuation mechanism that would allow independently controlling body rotations around the three body axes," he says. And that mechanism had to be sufficiently lightweight for the robot to be able to carry it. The flight of fruit flies provided the key. Karasek programmed his robot to mimic their hypothesized flight biomechanics.

It worked like a charm, and the result is the prototype DelFly Nimble flying robot. The robot's wings beat 17 times per second, generating lift and also making the robot capable of controlling flight direction by slight adjustments in wing motion. It can hover and fly in any direction (up, down, forward, backward, and sideways), as well as perform banked turns and 360-degree flips, akin to loops or barrel rolls—just like a fruit fly, despite being significantly larger than the insect. It also boasts excellent power efficiency, capable of hovering for five minutes or flying more than a kilometer on a single charge.

"In contrast to animal experiments, we were in full control of what was happening in the robot's 'brain,'" says Karasek. "This allowed us to identify and describe a new passive aerodynamic mechanism that assists the flies... in steering their direction throughout these rapid banked turns."

So there is no need for a feedback mechanism for fruit flies to perform their evasive maneuvers as quickly as possible.

"The robot opened up new possibilities of studying insect flight," says Karasek. "But it is also a new type of flying robot with unique capabilities."

Insect-inspired drones hold a lot of potential because they can fly more efficiently, with better maneuverability, than the standard drones currently available. The DelFly Nimble is also relatively cheap to manufacture, since it builds on existing manufacturing processes and uses off-the-shelf components.

DOI: Science, 2018. 10.1126/science.aat0350 (About DOIs).