Aeroelastic tailoring of composite couplings and blade geometry of a helicopter rotor using optimization methods

An aeroelastic analysis based on a finite element method in space and time is developed for an advanced geometry composite rotor, Optimization studies are carried out for a four-bladed, soft-inplane hingeless rotor with variable sweep, anhedral and planform taper, and with a two-cell composite box-beam spar, The objective function includes vibratory hub loads and vibratory bending moments; constraints are imposed on blade rotating frequencies, aeroelastic stability and autorotational inertia. Design variables include ply angles of the laminated walls of the box-beam, sweep, anhedral and planform taper, and nonstructural mass and its chordwise offset from the elastic axis, Aeroelastic optimization is performed for different combinations of design variables. The starting design is a straight blade with no composite coupling. Compared to the starting design, an optimized solution achieved a reduction in the 4/rev loads of 40-60 percent, and 15-25 percent in the peak-to-peak vibratory flap and lag bending moments.