Self-feathering rotary wing

A lifting rotary wing comprising

• a hub mounted on a shaft,
• a number of lifting rotor blades mounted to radial arms of said hub by bearing mans for feathering displacement about a spanwise pitch-change axis, and
• elastic spring means for cyclic adjustment of blade pitch in sinusoidal manner once per revolution of the rotary wing,
• Wherein
• said pitch-change axis of each lifting rotor blade is a first spanwise line in the blade which passes through the centers of gravity of all spanwise blade segments, and
• each blade has a second spanwise line which passes through the aerodynamic centers of all spanwise blade segments, said aerodynamic center line coinciding with said pitch-change axis except in a spanwise portion of the blade between radius r.sub.1 and r.sub.2 where the average chord is c.sub.x and the aerodynamic center line is located an average distance d.sub.x forward of the pitch-change axis, and
• moment of inertia of the blade I.sub.B measured about the blade pitch-change axis is related to the dimensions of said spanwise portion of the blade and feathering spring rate of the cyclic pitch control mechanism K.sub.s by the relationship ##EQU21## Where .OMEGA. is angular velocity of the rotary wing during flight, .rho. is air density at flight altitude and a is the non-dimensional lift curve slope of the blade airfoil, said combination of parameters producing a lifting rotor blade having natural feathering frequency lower than the speed of rotation of the rotor at all flight conditions, in which cyclic variations of aerodynamic lift produce cyclic feathering moments on the blade and resulting cyclic displacements in blade pitch lag behind said cyclic feathering moments by one half revolution of the rotor.

A lifting rotary wing comprising;

• a hub mounted on a shaft,
• a number of lifting rotor blades mounted to radial arms of said hub by axially slidable journal bearing means for feathering displacement about a spanwise pitch-change axis, and
• torsion-tension members which provide the total reaction to centrifugal force on each blade,
• Wherein
• said pitch-change axis of each lifting rotor blade is a first spanwise line in the blade which passes through the centers of gravity of all spanwise blade segments, and
• each blade has a second spanwise line which passes through the aerodynamic centers of all spanwise blade segments, said aerodynamic center line coinciding with said pitch-change axis except in a spanwise portion of the blade between radius r.sub.1 and r.sub.2 where the average blade chord is c.sub.x and the aerodynamic center line is located an average distance d.sub.x forward of the pitch-change axis, and
• moment of inertia of the blade I.sub.B measured about the blade pitch-change axis is related to the dimemsions of said spanwise portion of the blade and the dynamic feathering spring rate of the blade mounting K.sub.f by the relationship ##EQU22## Where .rho. is air density at flight altitude and a is non-dimensional lift curve slope of the blade airfoil, said combination of parameters producing a lifting rotor blade having natural feathering frequency lower than the speed of rotation of the rotor at all flight conditions, in which cyclic variations of aerodynamic lift produce cyclic feathering moments on the blade and resulting cyclic displacements in blade pitch lag behind said cyclic feathering moments by one half revolution of the rotor.