Meeting Abstract

43.2  Monday, Jan. 5  Aerodynamics of the northern flying squirrel (Glaucomys sabrinus) BAHLMAN, Joseph Wm*; RISKIN, Daniel K.; IRIARTE-DIAZ, Jose; SWARTZ, Sharon; Brown University; Brown University; University of Chicago; Brown University joseph_bahlman@brown.edu

Most studies on mammalian gliders deduce glide aerodynamics from the location of the launch and landing, using an assumption of steady-state aerodynamics. During steady-state gliding, all forces are balanced, velocity is constant, and motion is passive, powered only by gravity. However, considering the dynamic nature of the wings structure (articulated limbs and compliant membranes with muscles imbedded in the skin) and the complex forest environments where the animals glide, the assumption of steady-state aerodynamics may not be warranted. To test the hypothesis that mammalian gliders use steady-state aerodynamics we used high speed video to record the 3-D trajectories of wild flying squirrels over a variety of glide distances in their natural habitat. From these trajectories, we calculated velocities, accelerations, forces, force coefficients, glide ratios, and lift-to-drag ratios. Our results show that flying squirrels do not use steady-state aerodynamics at any point in glides of any of the distances examined. Instead, the squirrels generate more net aerodynamic force than their bodyweight, allowing significant upward and forward accelerations. Additionally, the squirrels show changes in their force coefficients and lift-to-drag ratios during glides, indicating active and coordinated control of non-steady glide paths. This way, squirrels achieve the same glide ratio as they would using steady-state aerodynamics, but with considerably greater total and horizontal velocity. Because the squirrels are able to change force coefficients, and redirect force upward or forward by adjusting the lift-to-drag ratio, they are able to modulate their lift and thrust generation.