Bats exhibit a high degree of agility and provide an excellent model system for bioinspired flight. The current study investigates an ascending right turn of a H. pratti bat and elucidates on the kinematic features and aerodynamic mechanisms used to effectuate the maneuver. To initiate and sustain the turn, the bat utilizes roll and yaw rotations of the body to different extents synergistically to generate the centripetal force for a stable turn. The turning moments are generated by drawing the wing inside the turn closer to the body, by introducing phase lags in force generation between the wings and redirecting force production to the outer part of the wing outside of the turn. Deceleration in flight speed, an increase in flapping frequency, shortening of the upstroke, and thrust generation at the end of the upstroke was observed during the ascending maneuver. The bat consumes about 0.67 W power to execute the turning ascending maneuver which is approximately two times the power consumed by similar bats during level flight. Upon comparison with a similar maneuver by a H. armiger bat [P. Windes, D.K. Tafti, R. Müller, Kinematic and aerodynamic analysis of a bat performing a turning-ascending maneuver, Bioinspiration and Biomimetics. 16 (2020). doi:10.1088/1748-3190/abb78d.], some commonalities as well as differences were observed in the detailed wing kinematics and aerodynamics.

The bat used for current study is an adult female Pratt’s roundleaf bat (Hipposideros pratti) weighing 55 g. The animal was kept with a group of conspecifics in a controlled indoor environment designed to allow natural movement given its typical flight behavior. Ethical procedures according to Virginia Tech’s Institutional Animal Care and Use Committee (protocol number 15-067) were followed. Kinematic data were collected using an optical 3D motion capture system put together inside a 1.2 m×1.2 m×5 m open-ended flight tunnel. The system comprised of 21 synchronized video cameras arranged in 3 rings located about 40 cm apart. The details of the camera specification and their arrangement is given in a prior work [P. Windes, X. Fan, M. Bender, D.K. Tafti, R. Müller, A computational investigation of lift generation and power expenditure of Pratt’s roundleaf bat (Hipposideros pratti) in forward flight, PLoS One. 13 (2018) 1–26. doi:10.1371/journal.pone.0207613.]. After being released, the bat flew without interruption through the tunnel and the camera arrays recorded the flight featuring different maneuvers at 120 frames per second and in 1920×1080 pixel resolution. The camera array was calibrated using the Svoboda multi-camera self-calibration method [T. Svoboda, D. Martinec, T. Pajdla, A convenient multicamera self-calibration for virtual environments, Presence Teleoperators Virtual Environ. 14 (2005) 407–422.doi:10.1162/105474605774785325.].

The recorded flight path consists of 3 full wingbeat cycles and an extra half-cycle at the end, i.e., 3.5 wingbeat cycles, captured over 55 video frames during which the bat executes an ascending right turn with deceleration in the flight direction similar to Windes et al. [P. Windes, D.K. Tafti, R. Müller, Kinematic and aerodynamic analysis of a bat performing a turning-ascending maneuver, Bioinspiration and Biomimetics. 16 (2020). doi:10.1088/1748-3190/abb78d.]. Each cycle is defined to start with an upstroke and end with a down-stroke. The last half cycle (upstroke) is included in spite of the second half of the cycle (down-stroke) being incomplete as the bat continues to ascend outside the range of the motion capture system. After the last upstroke that was analyzed in the current paper, the bat completes two full flaps before perching on the ceiling of the tunnel.

In order to track the wing motion, about 150 small white circular markers made of medical tape were set to the bat’s wings to capture the detailed spatio-temporal kinematic features of the wing as it effectuates the maneuver. Stereo triangulation was performed for the 55 frames of the current flight using a custom MATLAB code to achieve a total of (150 points) × (55 frames) ~ 8250 points in 3D space. In the event of spatial or temporal occlusions among those points, a temporal spline curve and a spatial implicit surface reconstruction [P. Windes, D.K. Tafti, R. Müller, Determination of spatial fidelity required to accurately mimic the flight dynamics of a bat, Bioinspiration and Biomimetics. 14 (2019). doi:10.1088/1748-3190/ab3e2a.] was used to fill in the missing data. Afterwards a 3D reconstruction was done using a MATLAB code where a semi-automated technique was used to define point correspondences between frames, the details of which are described in previous works [P. Windes, D.K. Tafti, R. Müller, Kinematic and aerodynamic analysis of a bat performing a turning-ascending maneuver, Bioinspiration and Biomimetics. 16 (2020). doi:10.1088/1748-3190/abb78d.], [P. Windes, D.K. Tafti, R. Müller, Determination of spatial fidelity required to accurately mimic the flight dynamics of a bat, Bioinspiration and Biomimetics. 14 (2019). doi:10.1088/1748-3190/ab3e2a.], [P. Windes, X. Fan, M. Bender, D.K. Tafti, R. Müller, A computational investigation of lift generation and power expenditure of Pratt’s roundleaf bat (Hipposideros pratti) in forward flight, PLoS One. 13 (2018) 1–26. doi:10.1371/journal.pone.0207613.].

Description of uploaded files and codes:

1. Maneuvering_flight_trajectory.mp4 = Bat flight video recording.

2. Raw_data_for_an_ascending_right_turn_of_Hipposiderous_Pratti.xlsx = x, y, z coordinates of the wing marker points making up the 3D wing kinematics.

3. ctr_pts.ucd = Connectivity information for the triangulated marker/control points on the wing surface.

4. surfgrid.s001 = Surface grid (fine resolution) used as an input for CFD.

5. splines.dat = This file contains the time dependent kinematic information of the flight trajectory for all the control points on the wing surface (discrete time step used = 1/120 s).

6. ibm_movement_bat.f90 = Fortran subroutine that reads the bat wing surface grid (surfgrid.s001), the connectivity information (ctr_pts.ucd) and the spline data (splines.dat) to generate the wing kinematics to be used as a boundary condition for CFD calculations.

7. ibm_force_all.dat = This file contains the aerodynamic force information on the bat wing coming out of the CFD simulation. The 11 columns are respectively, time, total force in x direction, total force in y direction, total force in z direction, pressure force in x direction, pressure force in y direction, pressure force in z direction, shear force in x direction, shear force in y direction, shear force in z direction and power

8. animation1.avi = This is an animation showing the wing perturbation of the bat as it follows the trajectory. This animation shows the pressure difference between the top and bottom surface of the bat wing calculated from the CFD simulation.