Aeroelastic optimization of a helicopter rotor to reduce vibration and dynamic stresses

Optimization studies are carried out for a four-bladed, soft in-plane hingeless rotor consisting of a two-cell composite box-beam span The design variables are the ply angles of the box-beam walls. The objective functions are the vibratory hub loads and the vibratory blade bending moments; constraints are imposed on blade rotating frequencies and aeroelastic stability. The objective functions are first minimized individually, and then a combined optimization is performed to minimize both the objectives simultaneously. As compared to the starting design, the optimum solution results in a 15-60% reduction of the 4/rev hub loads as well as a reduction in the peak-to-peak flap and lag bending moments of 11 and 14%, respectively Starting from an initially infeasible starting design with a 3% requirement on lag mode damping, the optimum solution with composite chordwise bending-torsion coupling results in an increase in fag mode damping of over 200% compared to the starting design.