The Physics of Bio-Inspired Covert Flaps As Flight Control Devices

Abstract Covert-inspired flaps are novel feather-inspired aerodynamic control surfaces that enable stability augmentation and maneuvering in small-scale Uncrewed Aerial Vehicles (sUAVs), especially for tailless configurations. For the first time, this paper uses time-averaged particle image velocity (PIV) to reveal the effect of static covert-inspired flaps on the flow field when simultaneously deflected on a wing’s upper (suction) and lower (pressure) surfaces. Compared to a flap deployed on a single side, the simultaneously deflected flaps enhance the modulation range of the aerodynamic response (i.e., lift, drag, and pitching moment), making them more effective as control surfaces. Results reveal two categories explaining why the modulation range of the simultaneous deflection response is larger than each side deflection alone. Limit-bounded cases, where the response is within the bounds of the single-sided experiments, and limit-expanding cases, where the interaction between the suction and pressure sides flaps is crucial. Limit-expanding cases are associated with flow fields with increased wake size or flow features that cannot be reconstructed from the suction-only or pressure-only flow fields. Using the velocity fields, we also show that superposition better predicts post-stall responses than pre-stall responses because the flow features present in the wake of the post-stall flow are similar between suction-only, pressure-only, and simultaneous deflection experiments. Finally, we show that the post-stall flow is more sensitive to pressure side flaps than suction side flaps due to significant flow changes occurring at the pressure side when the pressure side flap is deflected, which can increase the size of the wake and significantly alter the response. The results from the flow fields support the data-driven aerodynamic models that express the lift, drag, and pitching moment as a function of the flow and flap parameters.