Roll control via active flow control: From concept to flight

This paper describes a series of experiments that enabled a flight demonstration of roll control without moving control surfaces. That goal was achieved using a wing with a partial span Glauert-type airfoil, characterized by an upper-surface boundary-layer separation from the two-thirds chord location at all incidence angles. The flow over that region was proportionally controlled using zero-mass-flux unsteady excitation emanating from piezofluidic actuators. The control was applied to one wing at a time, resulting in gradual suppression of the boundary-layer separation, increased lift, and reduced drag, leading to a coordinated turning motion of the small electric drone. The extensive multidisciplinary study (starting from the actuator adaptation, the airfoil integration, and the twodimensional wind-tunnel tests) led to the selection of a configuration for the flight demonstrator. Further development of a lightweight wing and piezofluidic actuators, along with a compact, lightweight, energy-efficient electronic drive system, was followed by full-scale wind-tunnel tests and three successful flight tests. It was flightdemonstrated that active flow control can induce roll moments that are sufficient to control the vehicle flight path during cruise, as well as during landing. A linear model was used to predict the roll motion of the active-flowcontrolled drone, with reasonable agreement to the flight-test data. The current study resulted in several pioneering (to the best of our knowledge) achievements that should pave the way to further integration of active-flow-control methods in flight vehicles for hingeless flight attitude and flight-path control, as well as improved performance and increased reliability with lower observability.