Aeromechanical Stability Of A Bearingless Rotor Helicopter With Double-Swept Blades

The rotor blade double-swept-tip geometry can effectively improve the aerodynamic and aeroacoustic behaviors of a rotor. However, the aeroelastic or aeromechanical behaviors of a double-swept rotor helicopter are a challenge to helicopter flight safety and need to be investigated. In this paper, the aeromechanical stability of a bearingless rotor helicopter with double-swept blades is studied. The analytical model of the double-swept blade rotor/fuselage coupled system is developed by using 10 coordinate systems to describe the motion of an arbitrary point in the double-swept blade. The influences of the double-swept parameters including the inner swept-forward angle, outer swept-back angle, outer droop angle, and junction position of double-swept parts on the aeromechanical stability in ground contact condition and for the forward flight condition are investigated. Analytical results show that the double-swept blade can increase the critical rotational speed in the ground contact condition and improve the aeromechanical stability in forward flight. The outer droop angle can stabilize the rotor/fuselage coupled system. Parameters related to the outer swept-back part generally have more influence on the stability than those of the inner swept-forward part. The influence of the double-swept blade on the aeromechanical stability increases with increasing the swept-back angle of the outer swept-back part and decreases with increasing the starting position of the outer swept-back part.