Bats are famously the only mammal with true flight, as opposed to say "flying" squirrels, which glide. Now engineers at Brown University have answered that question on man's mind for millennia: Given that bats have wings made of thin skin stretched between bones, not rigid wings like birds and bugs - how do they do it?
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The answer, says the scientific team headed by grad student Jorn Cheney, lies in specially evolved hair-thin muscles in their wing skin that control the wing stiffness and curvature. And now the team is elaborating on its discoveries with the help of a robot bat wing.
The bat wing consists mainly of skin stretched over stupendously long fingers. It is flying with its forearms, if you will. Changing in wing rigidity and shape help the bats maneuver in the air, says the team, based on research on fruit bats equipped with electrodes on their wings. Interestingly, the study was financed in part by the U.S. Air Force.
“Aerodynamic performance depends upon wing shape,” said Brown biology graduate student Jorn Cheney, lead author of the newly published paper in Bioinspiration and Biomimetics, in a statement. Now, the wing membrane would start a flight flat, but the moment the bat "takes off" and the wing experiences lift, the membrane will change curvature in response to the aerodynamic burden.
Using these newly discovered muscles, plagiopatagiales, the bat can modulates skin stiffness and thereby controls the wing shape, he explains. These fine muscles would probably be pretty useless on their own: they act in coordination.
Testing their theories, the Brown group built an artificial bat wing, as students will do. The robot wing is being used to run experiments they couldn't humanely do on bats, like wing-beat frequency and amplitude, or the degree of wing folding during flapping, the team says. Live bats wouldn't like that. The group is now improving the robotic wing by integrating the new findings about how plagiopatagiales impact wing stiffness and shape.