Abstract: The invention relates to a method for determining a vortex geometry change of rotor vortices which are formed on a rotor which comprises a plurality of rotor blades. A dynamic lift distribution on the rotor plane is determined as a function of a lift change, which is correlated with n-times the rotor rotation frequency, on the rotor blades, from which the associated induced vertical velocities on the rotor plane can then be determined. The vortex geometry change is then calculated as a function of these induced vertical velocities.

Abstract: The invention relates to an approximation method for determining a change in vortex geometry at a rotor consisting of several rotor blades, where the rotor is located above the fuselage, with the steps: Determining a non-linear vertical velocity field, induced by the fuselage, by means of an analytic function of radial (polynomial approach) and azimuthal (Fourier series) in the rotor plane and calculating the vortex geometry change as a function of the induced.