An Examination Of The Relations Between Rotor Vibratory Loads And Airframe Vibrations

Harmonic rotor hub loads and airframe interactions in steady flight are reviewed, with regard to the objective of achieving lower airframe vibration by modifying blade root loads. Flight test and wind tunnel data are reviewed, along with sample fuselage response data. Trends which could provide a generalized approach to the above objective are found to be very limited. Recent analytical and corresponding experimental blade tuning modifications are reviewed and compared. Rotor vibratory load modification and substantial vibration changes were achieved over a wide range of rotor operating conditions. It is still concluded that improvement of blade tuning has the potential for reduction in airframe vibration. Current analytical methods are found not accurate enough to confidently predict effects of blade tuning on vibration. Test-based development of favorable blade configurations is shown to be feasible, and will also generate data to guide further development of analytical methods.