SI'KI-CTCR AI, OPTI\II7,ATIOX OF COJIPOSITE HEIJCOPTER ROTOR BI,AIILS WITH SWEPT nPs FOR VIBRATIOS REDUCTIOS n- FORWARD FIKHT

This paper describes the structural optimization of composite helicopter rotor blades with swept tips to minimize the Bjrev vibratory hub loads in forward flight subject to frequency and aeroelastic stability constraints. The acroelastic analysis is based on a modcrate dcflcction finite element model which is suitable for composite rotor blades with swept tips in hover and in forward fl~ght. Arbitrary cross-sectional shape, generally anisotropic material behavior, transverse shears and out-of-plane warping are included in the blade model. The optimization study is applied to composite blades with two-cell, hingeless configuration. Both soft-in-plane and stlff-in-plane blade configurations are analyzed. Ply orientation in the horizontal and vertical walls of the blade cross section and tip sweep and anhedral angles are selected as desigm variables. Sumerical results showing the effects of tip skveep, anhedral and composite ply orientation on blade aeroelastic behavior can be semed as a valuable precursor in selecting the initial design for the optimi~ation studies. IIowever, their proper combination for vibration reduction should be selected by the optimizer. Optimization results show that tip skveep has a significant influence on rotor vibration reduction.