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Hummingbird's flight decoded to advance aerodynamics

SAN FRANCISCO, March 24 — Researchers at Stanford University have unraveled the mechanics behind hummingbird's extended hovering flight mode, opening up possibilities to apply the technique to flying devices such as drones.

Hummingbirds are extremely skilled at "floating," being able to hover for long periods of time without stalling. Stanford's mechanical engineers, after working with almost a million samples of aerodynamic force, identified the perfect aspect ratio that makes this tiny bird so successful at flying.

David Lentink, assistant professor of mechanical engineering at Stanford of northern California, told Xinhua on Tuesday that the aspect ratio is critical to how a bird or a machine flies.

"We measured the wing aspect ratio, which is the ratio of the wing's length to its breadth or chord," said Lentink, who led the probe, "and saw that hummingbirds have a stubby aspect wing ratio, whereas helicopters, for example, have a slender one, which performs really well with low angles of attack, when the wings or blades are more horizontal to the ground."

Lentink and his colleagues mounted wings from museum specimens of Anna's hummingbirds to a spinning device, and monitored how air flowed around the wing as it beat in a pattern that mimicked hovering.

They found that more aggressive angles, meaning more vertical to the ground, make the airflow over the wings more unstable. The hummingbird, whose attack angle is very aggressive as it hovers to libate over flowers, creates a tornado-like vortex that prevents stalling.

"After many, many tests we found that the hummingbird's wings make a vortex that helps the flight thanks to its stubby wings. It takes a four chord length to maintain the right stability, which is why the slender helicopter blades would stall soon at a more vertical position," the researcher said.

This could also be the reason as to why insects and hummingbirds have very similar stubby wings and chord length, Lentink said, adding that the study, published in Britain's Journal of the Royal Society Interface, can help aerodynamic research.

"We are going to try to apply the hummingbird's wing aspect ratio to drones because if they can hover like the animal, they could even be used to help with disaster relief or hover near buildings," he said. "We can also make better turbines, because our study could help design wind turbines that would operate in urban areas or function as small grids." (PNA/Xinhua)

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