The seeds that twirl down from maple treesevery spring can fly as far as a mile, with each wing-shaped seed spinning like a whirligig on the air. Studies have shown that the seed’s whirling, called auto-rotation, gives it extra lift, but why this occurs has never been explained. It took an aerospace engineer, David Lentink of the Wagenigen University in the Netherlands, to figure it out [The New York Times].
Lentink and his colleagues first studied how a model of a maple seed moved in a tank of oil, and then filmed a real seed falling through a smoke-filled wind tunnel, which allowed them to observe the air currents around the seed. The images the team obtained showed that a swirling maple seed generates a tornado-like vortex that sits atop the front leading edge as the “helicopter” spins slowly to the ground. This leading edge vortex lowers the air pressure over the upper surface of the maple seed, effectively sucking the wing upward to oppose gravity [Live Science].
In the study, which will be published in Science, researchers say that this mechanism of staying aloft isn’t unique to the maple seeds. Such vortexes are also found in hovering insects and bats, and may represent “a convergent aerodynamic solution in the evolution of flight performance in both animals and plants” [Wired.com], the researchers write. The flapping wings of hovering hummingbirds also produce vortexes.
While the researchers are delighted to add to our understanding of the natural world, they say the work doesn’t have immediate applications. The vortex technique probably wouldn’t work at scales as large as an airplane, but the research could help in designing mini-parachutes that zoom in with a camera to survey the surface of a planet, Lentink says [Science News].
Image: David Lentink
