A hummingbird hovers like a dragonfly flies.
Hummingbirds flit and dart in a way that no other birds can. You hear the buzz of wings beating 50 to 200 times a second and see the iridescent plumage, but the tiny dinosaurs simply live life too fast for us to really figure out how they fly. To uncover how the hummingbird hovers, you would need a super-computer to analyze all the fluids those wings are flinging.
The team who simulated the wing beats of the birds — a pair of mechanical engineers from Vanderbilt University and a biologist at the University of North Carolina at Chapel Hill — first needed data. So they placed nine dabs of non-toxic paint on a female ruby-throated hummingbird’s wing and tracked their motion as the bird hovered with four cameras running at 1,00 frames per second.
Then the team produced the most detailed simulation to date of hummingbird flight. Using super-computers at the National Science Foundation’s Extreme Science and Engineering Discovery Environment (XSEDE) and Vanderbilt’s Advanced Computing Center for Research and Education, they simulated the thousands of tiny vortices in the air around the hummingbird’s wing to find out how it was keeping itself in the air. The result is mesmerizing, and informative.
If you’re a hummingbird, you can’t just flap your wings a few hundred times a second and hope to stay up, or even in the same place. What the simulation showed was the bird’s incredible control over the small instabilities in airflow that its wings create.
To maintain a hover, a hummingbird first tilts its wing down at the wrist (yes, birds have wrists) and completes a downstroke, which creates thousands of vorticies — like thousands of whirlpools — in the air. This turbulence forms an area of low pressure beneath the wing. As surrounding air rushes in to equalize the pressure, it generates lift. But the secret of hummingbird hovering is in the upstroke. When moving its wings backwards, the hummingbird again tilts its wings but in the opposite direction — as if it was another downstroke.
These upstrokes also generate lift, as if a rowing crew inverted the leading edge of their oars and dragged them back through the water after a stroke instead of raising them.
This lift-generating upstroke is why the hummingbird flies more like an insect. Many larger birds only use a downstroke to generate lift. On the upstroke they retract their wings to minimize drag. Dragonflies and other insects that hover, dart from place to place, and annoyingly dodge your hands use the same technique as the hummingbird. And though the hummingbirds are typically larger than these insects, the birds are able to keep their upstrokes surprisingly efficient — hummingbird upstrokes produce 30 percent less lift but use 30 percent less energy, making it as efficient as the downstroke, the team estimates.
Hummingbird wings may be different from insects’, but the basic physics is the same. Let’s hope that insects don’t pick up a hummingbird trait, however, and start stabbing throats in mid-air.
IMAGE: by Curt Hart
Kyle Hill is the Science Editor of Nerdist Industries. Follow on Twitter @Sci_Phile.