Roll control via active flow control: From concept development 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 part 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 Piezo-fluidic 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 collaborative and multidisciplinary study, starting from actuator adaptation, airfoil integration and 2D wind tunnel tests led to the selection of a configuration for the flight demonstrator. Further development of a light-weight wing, Piezo-fluidic actuators along with a compact, light-weight, energy-efficient electronic drive-system was followed by full-scale wind tunnel tests and three successful flight-tests. It was flight-demonstrated that active flow control (AFC) can induce roll moments that are sufficient to control the vehicle flight path during cruise as well as during landing. These were, to the best of our knowledge, first time achievements that should pave the way to further integration of AFC methods in flight vehicles for hinge-less flight attitude and flight path control as well as improved performance and increased reliability with lower observability.