Sunday, June 7, 2009

Dragonflies and Flight

Dragon flies are not easy to capture when one is leaning over a rocky edge precariously balanced above a form that cannot stay still.

Like a tiny helicopter the dragon fly hovers, its wings in perpetual movement.

A dragon fly has been an inspiration for can hover at will, instantly dart sideways or backwards, fly as fast as 30 mph and lift up to 15 times its own weight.
Recent studies show that dragonflies use "unsteady aerodynamics," a mode of flying radically different from the smooth flight of airplanes and soaring or gliding birds. Dragonfly wings churn up the air to create a whirling airflow that a dragonfly controls and uses to provide lift.

Dragonflies are relatively simple flying creatures. They each have two pairs of fairly rigid, transparent wings that are always extended. The front and rear pairs are not latched together, but operate independently. In addition, the insects don't change the shape of their bodies or wings in order to take off, glide or fly.

The researchers found that when a dragonfly's front pair of wings generates a small vortex of rapidly whirling air, the back pair, which may be down while the front pair is up or vice versa, captures the extra energy in that vortex's spin. This gives the air flowing over the top of a dragonfly's rear wing a much higher speed than the airflow along the wing's lower surface, and the wing generates more lift.

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