Helicopter Main Rotor Hub Load Alleviation Using a Variable Incidence Horizontal Stabilizer

A technique to reduce the main rotor hub forces and moments in high-speed maneuvers is proposed. The main working principle is a mechanical gearing ratio that distributes pitch commands from the (auto)pilot overmain rotor cyclic pitch and the horizontal stabilizer incidence angle. The optimal gearing ratio is determined by the weighted pseudoinverse method The system is analyzed with a nonlinear simulation model of the UH-60A Black Hawk helicopter. Results demonstrate that the main rotor shaft bending moment can be reduced by more than 50% for high-speed pitch maneuvers while maintaining almost identical predicted handling qualities as compared to the conventional method of control. All other hub forces and moments are also reduced significantly. The method also works effectively in off-design conditions. A safety analysis indicates that the system is safe for three failure cases considered. In the evaluation of the load alleviation system, it is proposed to use a fixed-wing handling qualities metric called flight path bandwidth.