Aeroelastic Optimization of an Advanced Geometry Composite Helicopter Rotor

Aeroelastic and sensitivity analyses based on finite element in space and time are used to carry out optimization studies for a four-bladed, soft-inplane advanced geometry composite rotor consisting of variable sweep, anhedral and planform taper, and with a two-cell 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, droop 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 17 and 26 percent, respectively, in the peak-to-peak vibratory flap and lag bending moments.