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Hummingbird flight could be mimicked by aerial vehicles

Hummingbirds occupy a unique place in nature: although they fly like insects, they have the musculoskeletal system of birds. Since they have extreme aerial agility and flight forms, many drones and other aerial vehicles are recently designed to emulate hummingbird movements. Now, by using a novel modeling method, a team of researchers led by Pennsylvania State University has gained new insights into how hummingbirds move their wings, which could lead to design improvements in artificial flying machines.

“We essentially reverse-engineered the inner working of the wing musculoskeletal system — how the muscles and skeleton work in hummingbirds to flap the wings,” said study lead author Suyash Agrawal, a mechanical engineer at Penn State. “The traditional methods have mostly focused on measuring activity of a bird or insect when they are in natural flight or in an artificial environment where flight-like conditions are simulated. But most insects and, among birds specifically, hummingbirds, are very small. The data that we can get from those measurements are limited.”

By using muscle anatomy knowledge, computational fluid dynamics simulation data, and wing-skeletal movement information captured through micro-CT and X-ray techniques, along with an optimization algorithm based on evolutionary strategies, the experts managed to design a model mimicking hummingbird flight.

“We can simulate the whole reconstructed motion of the hummingbird wing and then simulate all the flows and forces generated by the flapping wing, including all the pressure acting on the wing,” explained study senior author Bo Cheng, an associate professor of Mechanical Engineering at Penn State. “From that, we are able to back-calculate the required total muscular torque that is needed to flap the wing. And that torque is something we use to calibrate our model.”

The scientists discovered that hummingbirds’ primary muscles do not only flap their wings in a simple back and forth motion, but rather pull their wings in three directions – up and down, back and forth, and twisting (or pitching) of the wing. Moreover, the researchers also noticed that hummingbirds tighten their shoulder joints in both the up-and-down direction and the pitch direction by using the same set of small muscles.

“It’s like when we do fitness training and a trainer says to tighten your core to be more agile,” Cheng said. “We found that hummingbirds are using similar kind of a mechanism. They tighten their wings in the pitch and up-down directions but keep the wing loose along the back-and-forth direction, so their wings appear to be flapping back and forth only while their power muscles, or their flight engines, are actually pulling the wings in all three directions. In this way, the wings have very good agility in the up and down motion as well as the twist motion.”

“Even though the technology is not there yet to fully mimic hummingbird flight, our work provides essential principles for informed mimicry of hummingbirds hopefully for the next generation of agile aerial systems,” he concluded.

The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.

By Andrei Ionescu, Staff Writer

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