Captivatingly agile, hummingbirds flit deftly from flower to flower or snatch insects in their narrow beaks. Even though people love to watch hummingbirds move, scientists haven't been able to figure out how exactly they are able to fly. Biologists from the University of North Carolina in Chapel Hill teamed up with mechanical engineers from Vanderbilt University in Tennessee to simulate the aerodynamics of a hummingbird in flight. They found that the bird's movement more closely resembles insects than other kinds of birds. The researchers published their findings in September in the Journal of the Royal Society Interface.
When large birds fly, they exert most of their force on the downstroke, applying almost no force when they lift their wings back up. But insects and hummingbirds put more energy into the upstroke, although their flight is still mostly powered by flapping their wings down. They're able to do this by essentially flipping over their wings at the top and bottom of the stroke.
Think of it like buttering a piece of bread: once you've dragged the butter to one side of the bread, you rotate the knife to spread the butter in a new direction. The wing, in this analogy, is the knife. The part of the wing at the front, or the leading edge, on the downstroke rotates to lead the wing back up again, pushing the air up and back. This creates low pressure above the wing, which generates lift and keeps the bird aloft. The result is a streamlined movement that makes the hummingbird more nimble and able to move from side to side.
To come to this conclusion, researchers put nine dabs of non-toxic paint at strategic parts of the wing of a ruby-throated hummingbird. As the bird hovered next to an artificial flower in the lab, the researchers snapped pictures of its movement at 1,0000 frames per second with four different cameras. Then, using a supercomputer, the engineers created a model of the bird and its movement by noting the placement of the paint spots. Here's the resulting fluid-dynamic model.
Hummingbirds are incredibly efficient fliers, and human-engineered products still aren't close. But a better understanding how they generate the forces at play could help engineers improve the function of our own flying machines.