Research On The Influence Of Tail Rotor Tilting And Movable Stabilator On Helicopter Performance/Flying Qualities And Designing Method

A design approach, focused on improving helicopter performance and flying qualities by tailrotor tilting and movable stabilator, is developed.As helicopter widely used, a major goal of current helicopter research is thus to increase thehelicopter performance and flying qualities. However, compared to the fixed wing aircrafts, as thevarious flight states and the strong coupling between the aerodynamics and control, this research isa challenging task. Furthermore, the helicopter design is even more complex when considering thetrade off between the performance and flying qualities at different flight conditions. In general,researchers use aerodynamic layout design to satisfy the performance index, and then raise theflying qualities by control system design. This design idea enhances the design difficultly of thecontrol system, and has limitation on flying qualities. High performance and flying qualities canbe achieved by considering the quality indexes at helicopter aerodynamic layout design stage, andthis method can decrease the control system design difficulty, while the aerodynamic layout designdifficulty increased. In this paper, based on the systematical analysis of tail rotor tilting andmovable stabilator technical characteristics, a comprehensive investigation is conducted onaerodynamic layout design, so as to improve helicopter performance and flying qualities.A high accuracy flight dynamic model, suitable for the analysis of helicopter flightperformance and flight qualities, is developed. The blade element theory and dynamic inflowtheory are used to model the rotor aerodynamics. Based on wind tunnel tests, the fuselage, tailrotor and stabilator aerodynamics are modeled. The interference of rotor wake and fuselagesidewash is considered in this model. The model is validated through UH60A helicopter.The effects of tail rotor tilting on helicopter performance and flight qualities at various flightstates are analyzed. In hover and transition flight states, tail rotor tilting can decrease helicopternose-up pitch attitude and required power, improve helicopter flight performance; in forward, tailrotor tilting increase helicopter nose-down pith attitude, decrease helicopter maximum flight rangeand maximum endurance；tail rotor tilting can also increase the coupling between helicopteraerodynamics and control.The tail rotor tilting angle design is conducted using an optimization method. Parametersensitivity analysis shows that the center of helicopter gravity position has significant effect on theangle design. The required power is chosen as the optimization objective, under constrains ofhelicopter pith angle, side wind hover ability and helicopter gravity center position, tail rotortilting angle is optimized.Numerical simulation is conducted to analyze the effects of movable stabilator on helicopter performance and flight qualities. The results show that movable stabilator has high influence onhelicopter longitudinal performance and flying qualities, but little influence on lateral. So thehelicopter longitudinal performance and flying qualities can be improved by reasonable design ofmovable stabilator angle variation law.A control system is designed for movable stabilator. Helicopter pith attitude at level flight, andthe dynamic coupling between collective pitch and pith attitude at cruise, is chosen as theoptimization objective respectively. By optimizing, the optimal angle change law of movablestabilator is determined. Based on sequential quadratic programming optimization method,structure of the controller is optimized. This method can simplify stabilator angle design process,avoid the unfavorable influence of tail rotor tilting, and improve helicopter performance and flyingqualities.