(via Wikipedia) Perhaps you've never noticed this, or you don't live near maple trees, but the seeds of maple trees fall ever so slowly and, depending on the impact of the breeze or wind force, can be carried for miles before they land. A recently published study in the journal Science shows us why this happens and the significance it might have for future aerospace technology.
The researchers, David Lentink from Wageningen University in the Netherlands and Michael H. Dickinson, from the California Institute of Technology (Caltech), studied the fall of the maple seed by creating a robot of the seed and measuring its flow in oil, instead of air, through a tank. Then, to verify the results, 32 specimens of real maple seeds were studied as they spun freely in a wind tunnel.
Both observations concluded that the maple seeds produce a tornado-like vortex at the front edge of the seed that creates extra lift, slowing the descent of the spinning seed as it falls. The researchers noted that the vortex of the seed is very similar to that created by birds, bats, and insects as they hover.
Below, a multi-flash photograph shows the auto-rotating descent of the maple seed.
Image: courtesy of David Lentink via Caltech press release.
Here is a short video of a spinning seed, with smoke and laser light around it to enable a clearer view of the action.
The research, published in the June 12, 2009 edition of Science, has implications for aerospace engineering, as smaller surveillance helicopters and parachutes are being developed that need to slow their descent.
"There is enormous interest in the development of micro air
vehicles, which, because of their size, must function using the same
physical principles employed by small, natural flying devices such as
insects and maple seeds," says Dickinson.
"This is still an open challenge for future aerospace engineers, and
our aerodynamic study of maple seeds could help design the first
successful powered 'maple' helicopters," he adds. Over the past four
years, Lentink, an aerospace engineer, has designed operational flying,
flapping, and morphing micro air vehicles, inspired by his insect and
bird flight research.
Caltech press release