Meeting Abstract
Amid the gusty conditions of the low atmosphere, birds routinely fly where air vehicles of the same scale would struggle severely or even fail. Crucially important to birds’ control abilities are their compliant, articulated flight surfaces, which offer aerodynamic load alleviation to help stabilize the torso and head. To gain understanding on these control mechanisms, we flew a barn owl (Tyto alba) through variable upward gusts and derived its wing and tail kinematics from synchronized multi-angle high-speed video. In all flights, the wings rotate upwards about the shoulder, yet the torso remains exquisitely stable; under the same conditions, a simulated owl with rigid wings is driven vertically off course. We conclude that the basic requirement for the observed stabilization is a shoulder hinge, which acts as suspension to modulate the transmission of initial aerodynamic load to the torso. That the torso stays consistently still in all flights suggests that wing inertia is particularly well tuned – hinge forces (hence motion) are all but eliminated as the gust is encountered, in the same way that jarring at the hand is cancelled out when a ball is struck with the sweet spot of a bat. The mechanism is fast and should reduce the active burden on the flight control system. Once wing elevation saturates and the suspension effect subsides, the wings pitch down, dumping yet more aerodynamic load to provide sustained rejection of the gust.
