Stiff-Inplane Tiltrotor Aeromechanics Investigation Using Two Multibody Analyses

This paper presents the development of two multibody dynami cs odels to predict the whirl-flutter stability of a stiff-inplane tiltrotor wi nd-tunnel model and correlates the predictions with experimental data. Comprehensive, multibody-b ased dynamics analyses of rotorcraft enable modeling and simulation of the rotor system at a high l evel of detail so that complex mechanics and nonlinear effects associated with control sy stem geometry and various types of hinges and joints are able to be considered. A parametric stu dy of key design variables, such as control system stiffness, pitch-flap coupling, and aerodyn amic compressibility was completed as part of this investigation, which may help to determine su itable design criteria for future stiff-inplane tiltrotor systems. Analytical results indi cate consistent capabilities of multibody dynamics analyses in predicting the stiff-inplane tiltrot or whirl-flutter stability and show generally good agreement with the experimental results. Both a nalytical and experimental results show the destabilizing effects of pitch-flap coupling and ae rodynamic compressibility on the whirl-flutter stability of a stiff-inplane tiltrotor where as both results also indicate that a reduction in control system stiffness has little effect on whirlflutter stability.