Flight Investigation of Coaxial Rotor Tip Vortex Structure

Tip vortex structure and velocities in coaxial rotor wake were investigated in the course of Ka-32 helicopter flight testing in hover and in level flight. A smoke visualization technique was used with smoke generators installed in blade tips. The tip vortex structure was filmed by a high-speed camera. Still frame processing technique and tip vortex velocity calculations are presented. Time averaged and local tip velocities are determined for tip vortices shed at zero and 180 degrees azimuths. Vortex velocities are presented as functions of flight speed related to ideal inductive velocity in hover. The results of a coaxial rotor wake geometry investigation are presented for several level flight speeds. The investigations were carried out jointly by Russian Flight Research Institute and KAMOV Company.