Stability analysis of extension-twist coupled composite rotor blades

In a tiltrotor aircraft the difference in the inflow and the rotor speeds between hover and forward fligth modes necessitates different blade twist and chord distributions. A passive blade twist control design, referred to as The Sliding Mass Concept, has been previously proposed by the authors for performance improvement of a tiltrotor aircraft. An optimization technique was utilized which resulted in 4.4% improvement in hover performance. In this paper a stability analysis has been performed for the optimum configuration. The analysis is based on Prony series fitting on the signal data obtained from the analysis of a multibody dynamics model excited in the first three wing modes by using appropriate initial conditions. The first three symmetric wing mode damping variations with respect to the cruise speed are presented. The results are compared with an XV15 baseline design. The analysis has shown that no significant changes occur in the damping characteristics of the proposed model and that the system is aerodynamically stable

Extension-twist coupling optimization in composite rotor blades

In a tiltrotor aircraft the difference in the inflow and the rotor speeds between hover and forward flight modes necessitates different blade twist and chord distributions. A passive blade twist control design, referred to as The Sliding Mass Concept (SMC), has been previously proposed by the authors for performance improvement of a tiltrotor aircraft. In this paper a multibody dynamics code, DYMORE, together with a cross-sectional analysis tool, SVABS, have been used to accurately model the proposed system. The performance improvement envelopes determined through the multibody dynamics process predict approximately 6% reduction in hover power requirement with no significant improvement in forward flight performance. An optimization process based on the Simulated Annealing method was utilized to improve the hover performance of the XV15 baseline design by maximizing extension-twist coupling of the structure with constraints on the airfoil geometry and torsional stiffness. The analysis resulted in 4.4% improvement in hover performance for 1.0 kg/m sliding mass value without any additional weight penalty compared to the baseline design. The results demonstrate the feasibility of the concept and show the additional flexibility the sliding mass provides for performance improvement of the vehicle