Meeting Abstract

S11.9  Friday, Jan. 7  Aerodynamic performance of feathered dinosaurs KOEHL, M.*; EVANGELISTA, D.; Univ. of California, Berkeley; Univ. of California, Berkeley cnidaria@berkeley.edu

The evolution of flight in theropod dinosaurs, one lineage of which led to birds, is the subject of lively debate and speculation. Although earlier studies of these animals focused on lift and drag, and thus horizontal distance traveled while airborne, they did not explore performance in complex environments where animals are subjected to perturbations and must maneuver around obstacles. Fossils of feathered dinosaurs in Cretaceous forest sites in China are important because they reveal a variety of early “experiments” in flight morphology, some perhaps transitional to birds and others not seen today. An example of the latter, Microraptor gui, a small dromaeosaur with flight feathers on hind limbs and tail as well as on forelimbs, enabled us to investigate effects of diverse aerodynamic surfaces aft of a body’s center of mass. We measured aerodynamic forces on physical models in a wind tunnel to quantify effects of different postures and appendage motions that have been debated. By measuring pitch, roll, and yaw moments as well as lift and drag, we assessed static aerodynamic stability (righting torques when perturbed) and control effectiveness (moments generated by motions of control surfaces), both of which affect maneuvering ability while gliding or parachuting through a complex forest habitat. While some leg postures render M. gui unstable (thus easy to maneuver), others are stable (thus hard to maneuver, but resistant to perturbation). Depending on body posture, asymmetric leg positions can cause roll but have little effect on yaw, while raising and lowering the tail or hind limbs can alter pitch. We used a motorized model of M. gui to study effects of simple forewing flapping, which improves average lift/drag, but does not alter body static stability or the control effectiveness of legs and tail.