EXPERIMENTAL VERIFICATION OF HELICOPTER BLADE DESIGNS OPTIMIZED FOR MINIMUM VIBRATION

An experimental program was conducted to demonstrate the capability of an automated modal-based design optimization analysis to predict helicopter blade structural properties leading to improved rotor vibratory characteristics. Nineteen articulated model rotor configurations were wind tunnel tested and the resulting vibratory responses were measured. Each configuration was based on a unique combination of mass distribution and structural stiffness, corresponding to designs developed to achieve alternative objectives. Three baseline rotor configurations were defined to have natural frequency placements spanning the range of traditional design practice. The optimization analysis was used to define additional configurations by minimizing hub modal shears, minimizing modal vibration indices, or placing blade natural frequencies. Test data are presented to appraise the relative merits of each of these design approaches in producing helicopter rotor designs with improved vibratory characteristics. The experimental results show that the modal-based optimization analysis can be used to tailor blade structural properties to achieve low vibration rotor designs.