Most bats hang upside down while resting, which means they employ some pretty nifty aerobatic techniques to stick their landing. In a recent study, researchers from Brown University examined how exactly bats use their relatively heavy wings to go from flying with their heads forward to hanging with their head down and feet up.
"When they come in to land they're not moving very fast, which makes it hard to generate the aerodynamic forces needed to reorient themselves," Kenny Breuer, co-author of the recent study from Brown's School of Engineering, said in a news release. "So the question is, how do bats get themselves in position to land?"
For their study, researchers trained bats to fly into a special flight enclosure and land on a small piece of mesh fixed to the ceiling. Using high-speed cameras and sophisticated computer models, researchers were then able to observe how the animals pulled off such a tricky maneuver. This revealed that their unique aerobatic tricks have a lot to do with wing-mass and inertia.
Bats have pretty heavy wings for their body size, compared to those of birds and insects. This is because their wings are hand-like appendages of bone, muscle, joints, tendons and skin, which all adds extra weight. Using this to their advantage, though, bats generate inertial forces that allow them to reorient themselves using a subtle wing maneuver they employ a fraction of a second before they land. This method is similar to how cats reorient themselves to always land on their feet.
Specifically, the high-speed cameras revealed bats retracted one of their wings ever so slightly when approaching the ceiling of the enclosure. However, their other wing remained fully extended and with each flap the bats were able to rotate a half turn, which helps put them in the perfect position to cling to the mesh feet-first.
To see how the bats reoriented themselves to fly forward again, researchers removed the mesh in subsequent trials. This revealed the animals perform a similar rolling maneuver using their weighted wings.
"What this tell us is that in bats, with their heavy wings, it's the inertial forces that are more important relative to aerodynamics," Breuer explained. "That's a bit of a counterintuitive conclusion. Normally you'd think that an animal would not want to have such massive wings. But here, it turns out that the mass can be used to some benefit."
Their findings, recently are published in the journal PLOS Biology, have implications in the development of human -made flying machines.
"From an engineering perspective, there's a lot of interest in drones and flying microvehicles," Breuer added. "Maneuvering or directing those robotic vehicles is a challenge. The idea here is that using redistribution of mass is not a bad approach to take."
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