The trajectory of the tip vortex of a reduced-scale, 1 m diameter, four-bladed rotor during hover is studied using vortex methods combined with a center of mass analysis approach. The objective is to develop analysis techniques capable of accurately characterizing the dynamical features of the unsteady wake produced by rotorcraft during hover, descent, ascent and forward flight conditions. Measurements of all three components of the velocity field are acquired using a stereo PIV system synchronized to capture up to 260◦ wake age of the vortex with 10◦ offsets during hover conditions. The nominal operating condition of the rotor is at a blade loading of CT / = 0.0645 and a rotational speed of 1240RPM, corresponding to Rec = 180,000. An area encompassing the 95% confidence region for the vortex 極tter reveals a noticeable anisotropic, aperiodic pattern over all wake ages, which has not been previously observed. The principal axis of the vortex 極tter also appears to align itself perpendicular to the slipstream boundary. An accurate characterization and prediction of the trajectory of the individual tip vortices can significantly enhance the ability to design rotors to meet specific performance targets such as reduction in fuselage vibrations, noise scattering and maneuvering noise as well as an alleviation in the resuspension of particles during brownout 德國LaVision PIV/PLIF粒子成像測速場儀