Numerical investigation of vortex ring state of tail rotor and uncontrolled rotation of helicopter

Vortex ring state, or settling with power condition, of tail rotor of helicopter Mi-17 is investigated by numerical methods of Computational Fluid Dynamics (CFD). Distinct shape of inflow-thrust curves is described and various flow patterns at different locations of the curve are identified. The shape of the curve is identified as a feature responsible for uncontrolled rotation of helicopter at the onset of vortex ring state at the tail rotor.