A longitudinal linear parameter-varying model of a gliding gull during wing morphing

Abstract

Birds actively morph the shape of their wings to control impressive maneuvers that often outperform similar-sized uncrewed aerial vehicles (UAVs). To identify how to effectively use insights from avian flight to enhance the maneuverability of future UAV designs, it is necessary to quantify the dynamics associated with wing morphing. Previous work developed linear time-invariant (LTI) models of a gliding gull across different fixed wing configurations but could not capture the flight dynamics associated with morphing between different wing configurations. Here, I filled this gap by implementing a linear parameter-varying (LPV) model with wing joint angles as scheduling parameters. This approach models nonlinear kinematic and gravitational effects while interpolating between LTI models at discrete trim points. With the resulting LPV model, I investigated the longitudinal response due to various extension trajectories of the elbow and wrist, including the linkage extension trajectory that is inherent to the skeleton. Furthermore, I optimized the extension trajectory given four key objectives: speed and pitch angle overshoot, speed rise time, and pitch angle settling time. The resulting trajectories indicate that the biologically relevant gull wing linkage structure does not guarantee optimal longitudinal flight dynamic characteristics and that birds likely require extension speed feedback for effective control. Developing an LPV model of a gliding gull brings us one step closer to identifying avian control mechanisms that may allow for avian-like flight in future highly maneuverable UAVs.