The invention relates to a wing unit, in particular a spar box for forming aerodynamically active surfaces of an aircraft, in particular airfoils, horizontal tail units, or rudder units of a plane.Aerodynamic improvements can be obtained due to a surface geometry of the aerodynamically active surfaces, which surface geometry is adapted to the respective operating state of the plane by using the actuating members and/or weight savings due to minimizing of structural mechanical loads of the wing unit.