During landing, birds deploy their alular feathers, or alula, to stabilize leading-edge vortex (LEV) flow over their outer hand-wing to augment flight control. Here, we investigate an alula-inspired high-angle-of-attack roll control concept termed the sliding alula which uses coordinated shifting of a pair of alulae to control the spanwise asymmetry and associated loading of alula-stabilized LEVs. In the current investigation, a Sliding-Alula Wing (SAW) is constructed and mounted to a free-to-roll rig in a wind tunnel. A custom autopilot board issues control commands to the servo-controlled sliding alula actuator and a 9-axis IMU grants state feedback. The response of the actuator is first characterized at various operating conditions by synchronizing static-load measurements of the SAW with dynamic actuation of the sliding alula. A proportional-integral roll command-tracking controller is then designed and controller performance and robustness is experimentally assessed with the SAW on the free-to-roll rig. The SAW is found to successfully track +/- 15 deg doublet roll commands with less than 3 deg overshoot and a rise time of around 0.5 seconds while regulating wing-rock-induced roll oscillations to below 5 deg. These results demonstrate a novel way to manipulate separated flows for flight control at high incidences without undesired transients associated with the formation and shedding of a dynamic stall vortex.
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