HEDRICK, TL; BIEWENER, AA; CFS, Harvard University: Linear Accelerations in the Flapping Flight of Cockatiels
We quantified whole body vertical, horizontal, and lateral accelerations in the flapping flight of cockatiels (Nymphicus hollandicus, n=4) in order to examine the mechanisms they employ in producing forces within a wingbeat and across a range of speeds. Accelerations were measured in cockatiels trained to fly in a wind tunnel over a range of speeds (1�15 m/s) using a set of three accelerometers mounted on orthogonal axes and attached dorsally to the birds. A fourth accelerometer was mounted on the posterior ventral surface to measure the accelerations due to rotation. The accelerometer recordings were oriented to standard XYZ axes by applying roll, pitch, and yaw angles calculated from a 3D kinematic reconstruction of the flight trials. The 3D reconstructions were obtained by direct linear transformation of points digitized from three synchronized, high speed (250 Hz) digital video cameras. We found that the peak accelerations in the vertical axis occurred early (phase=0.32) in downstroke and were well predicted by the inertial forces of wing motion. Peak accelerations in the forward and lateral axes occurred later (phase=0.43 and 0.54), suggesting that aerodynamic forces are more important than inertial forces in producing accelerations in these directions. Additionally, cockatiels are believed to employ a continuous vortex gait with a lift producing upstroke at intermediate flight speeds. Consistent with this, we found that average vertical accelerations during upstroke were greater at these intermediate speeds but the magnitudes were small (mean=-0.3 m/s2). However, the lifting upstroke does appear to counteract any downward inertial acceleration due to raising the wings in upstroke. We found no evidence for an aerodynamically active upstroke at other speeds. (Supported by NSF IBN-0090265)
