System Identification of Post Stall Aerodynamics for UAV Perching

For a UAV to perch on a wire, aircraft control systems which operate far outside typical operating envelopes must be developed. The relevant transient aerodynamics at high angle of attack are not addressed today by control-accessible aerodynamic models. In this work, we present a set of physically-inspired basis functions which have enabled system identifica-tion of a nonlinear aerodynamics model along perching trajectories. Data is collected using a motion capture system which, critically, allows free-flight data from real system trajec-tories to be gathered. When simulated forward, the identified model accurately predicts the observed perching trajectories, making it an indispensable tool for designing feedback controllers that stabilize perching trajectories. Nomenclature x state vector = x z θ φ x ̇ z ̇ θ ̇ φ̇T x, z position of CG in world coordinates θ pitch angle φ elevator angle α wing angle of attack V total velocity s subset of basis function indices (le + lh) distance from CG to elevator, m n number of basis functions in model u servo command ˆ̈x predicted x acceleration (world coords), m/s βxi linear contribution of basis function i to ˆ̈xp Q state-wise weighting for simulation error Subscript i Variable number p plane coordinates el elevator I.