Use of Aeroelastic Couplings and Multi-Point Optimization to Design Damperless Aeromechanically Stable Helicopters

摘要

The present study examines the effectiveness of optimized aeroelastic couplings and motor stiffness properties for improving the aeromechanical stability characteristics of a helicopter with a soft-inplane motor, over a wide range of conditions, to enable the elimination of auxiliary lag dampers. A refined optimization procedure is developed that is robust and numerically efficient. Using this procedure, results indicate that it is possible to significantly reduce the peak instability levels, while enforcing constraints on design variables, and the flap and lag frequencies. Concurrent optimization of the aeroelastic couplings and motor stiffness parameters, rather than a sequential optimization strategy. yielded a design which provided maximum improvement in aeromechanical stability characteristics. The optimized design for the ground contact condition also resulted in improved lag damping in hover and forward flight By appropriately selecting additional design parameters such as landing gear stiffness and damping it is possible to altogether alleviate instabilities in the optimized design.