Despite their relatively cumbersome wings, bats are champions of nocturnal aviation, a feat accomplished through an ingenious bit of aeronautical engineering.
Bats fold their wings inward while lifting them in flight, saving 65 percent of the energy that would be required to lift wings still outstretched, say Brown University researchers who used high-speed video to analyze the aerial kinematics of fruit bats.
Some birds fold their wings in a superficially similar way, but bat wings retract and fold with particular efficiency, almost like closing hands — which, after all, is what they are, as bat wings represent evolution’s repurposing of a mammalian forelimb for flight.
Though the researchers expected that energy savings provided by a fold-winged upstroke would come from reductions in drag, their calculations showed these to be minimal. Instead, as with a human arm, it takes far more energy to lift a wing that’s outstretched than one that’s retracted.
The findings were published Apr. 12 in the Proceedings of the Royal Society B and sponsored by the U.S. Air Force.
Video: High-speed video of a fruit bat flying in a wind tunnel. (Riskin et al./Proceedings of the Royal Society B)
Citation: “Upstroke wing flexion and the inertial cost
of bat flight.” By Daniel K. Riskin, Attila Bergou, Kenneth S. Breuer and Sharon M. Swartz. Proceedings of the Royal Society B, April 10, 2012.