A fluid dynamically effective surface of a device moving in a fluid, especially a lifting surface of a flying machine, has an elastic axis extending in the span direction of the surface, and an adjustable control surface. The lifting surface is elastically deformable in a bending direction and/or in a torsion direction about the elastic axis, due to and dependent on the adjustment of the control surface, while changing the induced fluid dynamic drag. A control and/or regulating arrangement is provided for adjusting the control surface in the sense of minimizing the induced fluid dynamic drag of the lifting surface.