Abstract. Previous research has indicated aperiodicity in the positions of tip vortices emanating from a rotor blade in hover. The objective of the current study is to develop an analysis of the tip vortex aperiodicity in hover and to validate it with measurements on a reduced-scale, 1m diameter, four-bladed rotor. A "vortex ring emitter model" was developed to study the statistics of the tip vortices emitted from a rotor during hover. The locations of tip vortex cores for wake ages ranging from 0 to 260 were measured on the reduced-scale rotor using a stereo PIV system. The blade loading for the reduced scaled rotor was Ct= = 0:044 and the blade rotational speed was 1520 RPM, which corresponds to a tip Reynolds number of 248,000. The 95 % con dence region for the position of tip vortex cores exhibited an anisotropic, aperiodic pattern, approximating an ellipse. Moreover, the principal axis of this ellipse appeared to align itself perpendicular to the slipstream boundary. The analytical model showed good correlation with experimental data in terms of the orientation and extent of the anisotropy. An empirical model for viscosity was also considered which helped model the core radius growth of the vortex ring with wake age.