Hedrick, T.L.*; Tobalske, B.W.; Biewener, A.A.: 3D Kinematic Analysis of Lift Production Over a Range of Speeds in Ring-necked Doves and Cockatiels

A central problem limiting our understanding of the aerodynamics of avian flight is the lack of 3D kinematic data of wing motion. The lift generated by a wing is proportional to 1) the square of incurrent air velocity (i.e. the velocity resulting from the bird’s forward progress and the motion of its wings), 2) the wing’s angle of attack, and 3) wingspan, all of which may be altered by a bird with flexible, flapping wings moving along a 3D path. To help clarify which of these parameters birds actually vary to fly at different speeds, we investigated 3D wing kinematics of cockatiels (Nymphicus hallandicus) and ring-necked doves (Streptopelia risoria) as they flew in a variable-speed wind tunnel at speeds of 1 to 15 m/s. To reconstruct the 3D coordinates of points marked on the wing and body, we used a direct linear transformation to merge the 2D views provided by 4, synchronized, Redlake high-speed video cameras (250 Hz). During downstroke in both species we found that angle of attack varied fourfold over the range of speeds studied, while incurrent air velocity varied by less than twofold and wingspan varied only slightly. Thus, flapping birds primarily manipulate lift generation over a range of speeds by varying angle of attack and secondarily by changing the downstroke velocity of the wing. (Supported by NSF IBN-9923699)