An Examination of Changes in Bat Flight Kinematics During Take Off

The powered flight of bats is unique in nature because of the agility that it allows them to achieve in comparison to other flying animals of equivalent size. One example of this is a bat’s ability to take off with no initial freestream velocity and transition to cruising flight over the duration of relatively few wing beat cycles. Bat’s wings are highly complex and have 20⁺ degrees of freedom (DOFS) per wing. Adjustments to several of these DOFS occur to allow for quick transition to cruising flight. In order to capture this transition in wing motion, video of Great Himalayan Leaf-Nosed Bats (Hipposideros Armiger) was captured over a period that included both take off and cruising flight. Images captured using a multi-camera setup, containing three rings of 10 RGB cameras each, were used in conjunction with triangulation techniques to capture the 3D coordinates of marker points on the wing. This setup eliminated the point dropout that can occur due to occlusion in traditional 2 camera systems due to its 360 degree coverage. Furthermore, the redundancy caused by collecting 3 or more 2D marker point projections from some of the 10 cameras per ring improved accuracy of the 3D coordinates. In order to capture the transition in wing kinematics, changes in flap amplitude, velocity, and frequency, were recorded. The data suggests that this species of bat utilize a change in flap amplitude as the primary means to transition from takeoff to cruising flight while keeping other parameters such as angle of attack and flap frequency constant.