Climbing Flight of a Fruit Bat Deconstructed

Abstract

The climbing flight flapping kinematics obtained on a fruit bat, Cynopterus brachyotis, is deconstructed using proper orthogonal decomposition to shed light on the functional kinematic modes which enables bat flight. Mode 1 and cumulative mode 1 + 2, compared against the native kinematic, is simulated in a Immersed Boundary CFD framework to observe the effect these modes have on the unsteady transient mechanisms of the flow produced by the flapping wings. From the obtained data, the bat exhibits fine control of its mechanics by actively varying wing camber, wing area, torsional rotation of the wing, forward and backward translational sweep of the wing, and wing conformation to dictate the fluid dynamics. As is common in flapping flight, the primary force generation is through the attached unsteady vortices on the wing surface. Mode 1 is seen to act as the power stroke dumping energy into the fluid. Mode 2 adds the mechanism which maneuvers the flow structures to enable forward flight.