Parametric Study of Tiltrotor Whirl Flutter Using Two Rotorcraft Comprehensive Analyses

This paper presents a parametric study of stiff-inplane tiltrotor whirl flutter using two rotorcraft comprehensive analyses: RCAS and DYMORE, correlating the predictions with experimental data. Comprehensive, multibody-based dynamics analyses of rotorcraft enable modeling and simulation of the rotor system at a high level of detail so that complex mechanics and nonlinear effects associated with control system geometry and various types of hinges and joints are able to be considered. A parametric study of key design variables, including control system stiffness, pitch-flap coupling, and aerodynamic compressibility was completed, which may help to evaluate the predictions and to determine suitable design criteria for future stiff-inplane tiltrotor systems. Analytical results indicate consistent capabilities of multibody dynamics analyses in predicting the stiff-inplane tiltrotor whirl-flutter stability and show generally fair to good agreement with the experimental results. Both analytical and experimental results show the destabilizing effects of pitch-flap coupling and aerodynamic compressibility on the whirl-flutter stability of a stiff-inplane tiltrotor whereas both results also indicate that a reduction in control system stiffness has little effect on whirl-flutter stability.