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 flight 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 percent 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.