Maple seeds stay longer in the air due to their similarity to insect wings

Written by Thomas Hesselberg

Tuesday, 16 June 2009

A maple seed with the heavy nut at the base and the wing shaped seed at the top. Photo courtesy of Wikimedia Commons (by user Kobako).

A new study on the aerodynamics of wind dispersed maple seeds show that these seeds descend slower, and thereby disperse wider, by attaching a vortex of air, which generates increased lift. A very similar mechanism is known from insects, where it helps generate the necessary flight forces.

Maple, like many other trees, relies on wind to disperse its seeds. To aid the dispersal the maple seeds have evolved a host of morphological adaptations. The heavy nut is at the base of the insect wing shaped seed and this arrangement causes the seed to rotate while falling towards the ground.

Scientists from the University of Wageningen in the Netherlands and Caltech in the United States were able to show that this rotation give rise to an aerodynamic phenomenon known as a leading edge vortex, (LEV) a swirling mass of air attached to the frontal edge of the seed. LEVs was discovered in beating insect wings, where they helped explain how relatively heavy insects with small wings, such as bumble bees, manage to generate enough forces to fly.

The scientists first proved the existence of the LEV in a dynamically scaled robot model of the seed moving in a tank of mineral oil. Then they filmed real rotating maple seed in a vertical wind tunnel with highspeed cameras and visualised the flow around the seed. The real seeds showed the same flow field as the robot model.

The scientists speculate that this mechanism could be used to design aerodynamically efficient auto-rotating devices.

Source:
Lentink, D., Dickson, W. B., van Leeuwen, J. L. & Dickinson, M. H. (2009). Leading edge vortices elevate lift of autorotating seeds. Science 324: 1438-1440.

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