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3D wing and body kinematics of the bats were reconstructed from the high-speed video using a model-based trackingalgorithm. This tracking system incorporates a Kalman filter and a priori biomechanical constraints to recover the complex motions of the flight maneuvers. With this method, the team extracted six degrees of freedom describing a bat’s body position and orientation, 23 joint angles describing the articulated pose of each of the bat’s wings, and 38 parameters describing the bat’s geometry (i.e. – shoulder and hip positions, body dimensions, and bone lengths.
With these methods, the team was able to find that when the bats approach their landing spot, they retract one of their wings ever so slightly toward their bodies, while flipping the other at full extension. With each wing beat in that asymmetric configuration, the bats rotate a half turn, helping to put them in position to meet the mesh feet first. When the team removed the mesh, the bats performed a similar rolling maneuver using their wings in order to reorient for forward flight.
A computer simulation was then used to confirm that the effect they were seeing was due to inertia rather than aerodynamics. The team used motion capture to record the bats’ movements and then replayed the movements through a computer simulation in which the effects of different forces could be switched on and off. When the simulation was run with aerodynamic forces turned off, the virtual bats were still able to recreate the motion of the real ones.
"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 said. "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."
While the research helps to shed light on the biology that helps bats fly and land the way they do, the team suggests that it may be useful in the development of human-made flying machines.
"From an engineering perspective, there’s a lot of interest in drones and flying microvehicles," Breuer said. "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."
The fullfindings of this research were published in PLOS Biology in November 2015.
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