STRUCTURAL OPTIMIZATION FOR VIBRATORY LOADS REDUCTION OF COMPOSITE HELICOPTER ROTOR BLADES WITH ADVANCED GEOMETRY TIPS

This paper describes the structural optimization of composite helicopt er rotor blades with swept tips to minimize the B/rev vibratory hub lo ads in forward flight subject to frequency and aeroelastic stability c onstraints. The aeroelastic analysis is based an a moderate deflection finite element model that 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 o ut-of-plane warping are included in the blade model. The optimization study is applied to composite blades with two-cell, hingeless configur ation. 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 th e design variables selected tip sweep appears to be the most influenti al design variable. Depending an the configuration considered and obje ctive function used, vibration reduction in vertical hub shears of the order 30-50 % from the baseline can be obtained.