The fastest swimming insect could inspire the design of unmanned boats

Swirling beetles, the world’s fastest swimming insect, reach surprising speeds by employing a strategy shared by fast marine mammals and waterfowl, according to a new Cornell University study that rewrites previous explanations of physics involved.

Centimeter-long beetles can achieve a maximum acceleration of 100 meters per second and a maximum speed of 100 body lengths per second (or one meter per second).

Not only do the results explain the Olympian vortex speeds, they also offer valuable insights to bio-inspired designers of near-surface aquatic robots and unmanned boats.

Until now, researchers thought the vortices reached their impressive speeds thanks to a propulsion system called drag-based thrust. This type of thrust requires the insect’s legs to move faster than swimming speed, for the legs to generate thrust. For the whirling beetle to achieve such fast swimming speeds, its legs would have to push against the water at unrealistic speeds.

“That could have been questioned,” said Chris Roh, assistant professor of biological and environmental engineering. “Fastest swimmer and drag-based thrust don’t usually go together in the same sentence.”

In fact, fast-swimming marine mammals and waterbirds tend to forgo drag-based thrust in favor of lift-based thrust, another propulsion system. The discovery was described in a study published January 8 in the journal Current biology.

Using two high-speed cameras synchronized from different angles, the researchers were able to film a whirlwind and observe a lift-based thrust mechanism at play. Lift-based thrust works like a propeller, where the motion of thrust is perpendicular to the water surface, eliminating drag and allowing more efficient momentum capable of greater speed.

“In biology, it’s hard to rotate things,” Roh said. “We are contraction-based machines, so you could say that the whirling beetle’s legs are a partial helix that spins around an angle, then retracts before resetting and partially spinning again.”

In addition to leg and body velocities extracted from two synchronized camera observations, Sun used aerodynamic formulations to calculate that lift-based thrust accounted for most of the force required for the whirlwind’s rapid propulsion.

“It’s not that different from a slightly tilted airplane wing,” Roh said. “This angle of attack allows it to actually generate lift.”

Lift-based thrusting has previously been identified in large-scale organisms, such as whales, dolphins, and sea lions. “In this work, we extended the length scale up to a centimeter, which which means that whirling beetles are by far the smallest organism to use lift-based thrust to swim,” said Yukun Sun, a doctoral student in Roh’s lab and first author of the paper. author.

“We hope this will speak to bio-inspired robotics and other engineering communities to first identify good physics and then try to preserve that physics in creating robotics,” Roh said.

The U.S. Navy has developed unmanned boats because traditional ship design is limited by the need to make boats accommodating to a crew. By eliminating a crew, boats can be much smaller and more flexible. Roh believes the small size, ship-like shape, and vortex lift-generating propulsion mechanism translate well to informing the design of robotic ships.