An acorn may not fall far from the tree, but the same cannot be said for a maple seed, with its distinctive wing shape. As it falls, the heavier nut end of the wing causes it to whirl in the air, slowing its descent and allowing the wind to carry the seed, sometimes as far as a mile or more.

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 Wagenigen University in the Netherlands, to figure it out.

Dr. Lentink, with Michael H. Dickinson of the California Institute of Technology and colleagues, report in Science that the wings generate a leading edge vortex  a spinning horizontal tunnel of air along the wing  as they descend. This vortex is stable, Dr. Lentink said, because it has a low-pressure core that reduces the air pressure over the wing, causing the wing to be sucked up. “It really increases the lift,” he said.

Image Smoke particles illuminated with laser light around a freely flying maple seed reveal a prominent leading edge vortex. Credit... David Lentink

Dr. Lentink suspected that the seed might generate such vortexes; many wings do, given the right conditions. To prove it, he and his colleagues first created a model, a rotating robotic wing in mineral oil. The model was dynamically scaled, meaning it matched the aerodynamics of a real seed in the air.