Vortex generators (VGs) are being used to prevent flow separation and stall on wind turbine blades. Optimal VG designs are chosen from steady investigations, assuming similar separation control characteristics between steady and unsteady conditions. Surface pressure measurements on a thick pitching airfoil with VGs show that VGs larger than the optimal steady size and rectangular VGs instead of the common triangular VGs must be used to consistently prevent unsteady flow separation and dynamic stall.