Individual Blade Root Control of Helicopter Blade Sailing for Articulated Shipboard Rotors

This paper investigates an individual-blade-root-control approach to the reduction of helicopter blade sailing and suppression of tunnel strikes for articulated rotors, considering steady flow conditions during engagement shipboard operations. The aeroservoelastic modeling includes a nonlinear structural dynamics related to the droop and flap stops, a linear aerodynamic model based on the blade-element theory, a linear gust model for the ship airwake, and a lift compensator. The blade-sailing model is a forced parametric flapping oscillator with nonlinear stiffness and time-varying coefficients. The aeroelastic control law design yields a flap-state-feedback individual-blade-root controller for the lift/angle-of-attack compensation whose parameters are associated with the damping/stiffness enhancement of the flapping oscillator. The simulation results show that the proposed active aeroelastic controller yields blade-sailing reduction of nearly 30% in upward and downward deflections at severe wind-over-deck conditions by using low blade pitch input limits of the actuators. This blade-sailing reduction can prevent tunnel strikes from occurring. The relaxation of the actuator limits can significantly improve the attenuation of the blade deflections.