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

A new technique to reduce the main rotor hub forces and moments at high speed maneuvers is proposed. The main working principle is a mechanical gearing ratio that distributes pitch commands from the (auto)pilot over main rotor cyclic pitch and the horizontal stabilizer incidence angle. The optimal gearing ratio is determined by the weighted pseudo inverse 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 whilst maintaining almost identical 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 proposed system, a new handling qualities metric called flight path bandwidth is proposed.