OPTIMIZING TUNING MASSES FOR HELICOPTER ROTOR BLADE VIBRATION REDUCTION AND COMPARISON WITH TEST DATA

This article describes the development and validation of an optimizati on procedure to systematically place tuning masses along a rotor blade span to minimize vibratory loads. The masses and their corresponding locations are the design variables that are manipulated to reduce harm onics of hub shear for a four-bladed rotor system without adding a lar ge mass penalty. The procedure incorporates a comprehensive helicopter analysis to calculate the airloads. Predicting changes in airloads du e to changes in design variables is an important feature of this resea rch. The procedure was applied to a one-sixth, Mach-scaled rotor blade model to place three masses and then again to place six masses. In bo th cases the added mass was able to achieve significant reductions in the hub shear. In addition, the procedure was applied to place a singl e mass of fixed value on a blade model to reduce the hub shear for thr ee flight conditions. The analytical results were compared to experime ntal data from a wind-tunnel test performed in the Langley transonic d ynamics tunnel (TDT). The correlation or the mass location was good an d the trend of the mass location with respect to flight speed was pred icted fairly well. However, it was noted that the analysis was not ent irely successful at predicting the absolute magnitudes of the fixed-sy stem loads.