Helicopter rotor dynamics optimization with experimental verification

An automated design optimization analysis was developed to efficiently predict helicopter blade structural properties leading to improved dynamic behavior. Modal-based optimization criteria were defined for calculation by a coupled-mode eigenvalue analysis. The optimization analysis was applied to various rotor dynamics problems to predict potential design benefits and evaluate techniques for improving optimizer performance. Design parameter scaling, algorithm selection, and objective function formulation were shown to have a significant influence on optimizer performance. Two experimental programs were also conducted to verify the analysis. In each program, formal optimization techniques were applied to modify the structural properties of dynamically scaled models to improve certain operating characteristics. In the first, the edgewise structural bending-stiffness distribution of a bearingless rotor model flexure was optimized to maximize the edgewise structural damping ratio, while maintaining acceptable blade frequency placement. In the second, the blade spanwise mass distribution and structural bending stiffness of an articulated rotor model were varied to minimize rotor vibratory loads in forward flight. Direct comparison of experimental results from baseline and optimized rotors for each test program verified the reliability of the selected optimization criteria and showed that the modal-based analysis can be used to achieve significant improvements in aeromechanical stability and rotor vibratory response.