Experimental and numerical analysis of the stability of an autogyro teetering rotor

The periodic behaviour of a rotor undergoing autorotation remains poorly understood. We present in this paper a systematic investigation into the stability of autorotating rotors, particularly teetering rotors. The investigation was conducted through analytical studies using continuation and bifurcation methods and practical wind tunnel experimentations. Our numerical evaluation is in close agreement with the experimental analysis in terms of generating bifurcation diagrams that dictate regions of stable and unstable autorotation behaviour. At various flow speeds, we found that loss of stability for lightly loaded rotors is due to the presence of fold bifurcations. We have also shown that lightly loaded rotors, at higher forward speed, are more susceptible to instability due to the smaller region of attraction of the stable autorotation branch. Furthermore, rotors in autorotation were demonstrated to autorotate at two different rotational velocities for the same flow speed in selected parameter regions. Finally, the loss of symmetry in the rotor blade flapping behaviour due to the existence of a branch point bifurcation was addressed.