Abstract: To reduce vibration of movable airfoil structures, such as rudders, elevators, and ailerons, a spring device, a leaf spring for example, is mounted to an airfoil mounting structure, such as a vertical tail plane, horizontal tail plane or the wings, such that the spring device exerts a force on a cam device, which transforms the spring force into an airfoil torque. The airfoil torque is applied to the airfoil structure and thus reduces a risk of vibration. The cam device is configured to redirect the spring force such that when the airfoil structure is moved in a first direction, torque decreases and when moved in the opposite second direction the torque is zero.