Active control of helicopter blade stall

This paper describes the numerical analysis of an automatic stall suppression system for helicopters, The analysis employs a finite element method and includes unsteady aerodynamic effects (dynamic stall) and a nonuniform inflow model, The stall suppression system, based on a transfer matrix approach, uses blade root actuation to suppress stall directly, The results show that stall can effectively be suppressed using higher harmonic blade root pitch at both cruise and high-speed Eight conditions. The control amplitude was small, less than 1 deg, In a high-thrust, low-speed flight condition, stall is fairly insensitive to higher harmonic inputs. In general, stall suppression does not guarantee performance improvements, The results also show the distinction between stall suppression and performance improvement with active control. When the controller aims to reduce the shaft torque, rotor performance improvement can be achieved with a small degradation in stall behavior.