Meeting Abstract
P2.160 Tuesday, Jan. 5 Hindlimb movement of Cynopterus brachyotis during flight CHENEY, JA*; TON, D; RISKIN, DK; SWARTZ, SM; Brown University; Brown University; Brown University; Brown University jorn_cheney@brown.edu
Many discussions of bat flight focus primarily on the forelimb, but because the wings of bats are continuous with the entire hindlimb, the hindlimbs can also influence aerodynamics. We examined the kinematics of the hindlimbs of flying bats to determine whether leg motions are consistent with the hypothesis that hindlimbs play an active role in modulating wing shape during flapping flight. If the hindlimbs are actively shaping the wing, we expect that its movement would not passively follow the motion of the wing’s trailing edge. If the hindlimb does influence wing shape, we would predict that the dorsal orientation of the ankle would primarily explain changes in angle of attack. We also asked if hindlimb motion influences wing camber, given that movement of the ankle toward the midline of the body, away from the fifth digit, will lengthen the wing’s trailing edge and increase tension in the plagiopatagium. We flew five Cynopterus brachyotis (Pteropodidae) five times each in a wind tunnel over a range of speeds (3.2 – 7.8 m•s-1). We recorded the motions of several markers on the body, hindlimb, propatagium, and plagiopatagium using three phase-locked high-speed cameras, and reconstructed their 3D motions using the direct linear transformation method. As predicted, we found that the position of the ankle marker moved toward the midline and away from digit V, at some parts of the wingbeat cycle, and that the movement of the ankle in the dorsoventral direction preceded movement of the trailing edge. This suggests that the hindlimb plays an important role in actively shaping the membrane during flight. Thus, while both insects and birds modulate angle of attack and camber at the leading edge of the wing only, bats appear to be able to modify these parameters at the trailing edge. Interestingly, aircrafts and bats appear to have converged on similar systems of control in this regard.
