STRUCTURAL OPTIMIZATION, FOR VIBRATION REDUCTION, OF COMPOSITE HELICOPTER ROTOR BLADES WITH ADVANCED GEOMETRY TIPS SUBJECT TO MULTIDISCIPLINARY CONSTRAINTS

This paper describes the structural optimization of composite helicopter rotor blades with swept tips to minimize the B/rev vibratory hub loads in forward flight subject to frequency and aeroelastic stability constraints. The aeroelastic analysis is based on a moderate deflection finite element model which is suitable for composite rotor blades with swept tips in hover and in forward flight. 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 stiff-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 design variables. The optimization results obtained show that among the design variables selected tip sweep appears to be the most influential design variable. Depending on the configuration considered and objective function used, vibration reduction in vertical hub shears of the order 30-50% from baseline can be obtained.