Design optimization of a covert feather-inspired deployable structure for increased lift

Flying at low Reynolds numbers and at high angles of attack has always been a great challenge for unmanned aerial vehicles (UAVs). However, birds can easily perform these maneuvers in nature. Birds have passively-deployed feathers called covert feathers on the upper and lower surfaces of their wings. These feathers protrude into the flow to mitigate flow separation during high-angle-of-attack flight. This paper presents the design optimization of a single covert-inspired flap that is attached to the upper surface of an NACA 2414 airfoil. An evolutionary algorithim, known as The CMA-ES (Covariance Matrix Adaptation Evolution Strategy), is used for the design optimization. The objective function is to maximize lift and the design parameter is the flap deflection angle. The lift coefficient is calculated using an unsteady discrete vortex method (DVM). Preliminary results show that the optimal flap design improves lift up to 23% comparing with the clean airfoil at high angles of attack. This work is an important step towards achieving a spatially distributed deployable structures system, similar to the covert feathers, for separation control and stall mitigation in small unmanned air vehicles.