In recent years, there has been a renewed interest in thrust and lift compounded helicopters from most of the major helicopter manufacturers. In such a configuration, the main rotor is required to operate in autorotation. However, from past incidences it has been experienced that a rotor operating in autorotation at high speed can become unstable in flapping, potentially leading to total loss of the aircraft. Aeromechanical stability of a rotor in autorotation is a complex nonlinear phenomenon which involves interactions between almost all the sources of nonlinearities, namely; aerodynamic, kinematics, inertial and material property nonlinearities. The fact that the rotor speed is not held constant in autorotation means that existing methods used in studying the flapping stability of helicopter rotors are not adequate. It is, therefore, the objective of this study to show how bifurcation and continuation analysis tools can be adapted to understand the flapping behaviour of such a rotor. The results of this analysis show that these tools give a very good insight into the rotor periodic behaviour, where scenarios of blade flapping instability can be constructed from the bifurcation diagrams. Blade sailing instability and pull-up manoeuvre instability have been identified although the rotor model used here does not incorporate features of blade structural flexibility.
|Translated title of the contribution||The stability of rotor blade flapping motion in autorotation using bifurcation and continuation analysis|
|Title of host publication||32nd European Rotorcraft Forum, Maastricht, Netherlands|
|Publication status||Published - Sep 2006|