Blade-pitch control system with indexing swashplate

1. A blade-pitch control system for controlling a pitch angle of each of a plurality of blades on an aircraft rotor, the blades being rotatably connected to a yoke for rotation with a rotor mast, the control system comprising:

a swashplate assembly having a non-rotating portion and a rotating portion;

an indexing portion of the mast, the swashplate assembly being translatably affixed to the indexing portion;

a pitch link connecting the rotating portion of the swashplate assembly to each blade;

wherein translation of the swashplate assembly along the indexing portion causes a change in pitch of the blades and a corresponding indexing of the rotating portion of the swashplate assembly relative to the mast, the indexing causing a change in an angular orientation of each pitch link, thus providing for selected pitch-flap coupling between flapping motion of the yoke and pitch motion of the blades; and

wherein the indexing portion comprises curved splines connected to and causing indexing of the rotating portion of the swashplate.

2. The blade-pitch control system of claim 1 , wherein the curved splines are helical in shape.

3. The blade-pitch control system of claim 1 , wherein the curved splines have a non-constant curvature.

4. The blade-pitch control system of claim 1 , wherein an end of each pitch link connected to the rotating portion of the swashplate assembly trails the opposite end of the pitch link in one indexed position and leads the opposite end in another indexed position.

5. The blade-pitch control system of claim 1 , wherein indexing of the rotating portion of the swashplate assembly prevents contact of the pitch link with the yoke during operation.

6. The blade-pitch control system of claim 1 , wherein selective indexing of the rotating portion of the swashplate assembly causes rotation of each pitch link between an orientation that is substantially parallel to the mast axis and an orientation inclined relative to the mast axis.

7. A method of controlling a pitch angle of each of a plurality of blades on an aircraft rotor, the blades being rotatably connected to a yoke for rotation with a rotor mast, the method comprising:

(a) providing a swashplate assembly having a non-rotating portion and a rotating portion;

(b) connecting the rotating portion to an indexing portion of the mast; and providing curved splines on the indexing portion;

(c) connecting the rotating portion to the blades with pitch links; and

(d) translating the swashplate assembly along the indexing portion for causing a change in pitch of the blades and a corresponding indexing of the rotating portion of the swashplate assembly relative to the mast, the indexing causing a change in an angular orientation of each pitch link, thus providing for selected pitch-flap coupling between flapping motion of the yoke and pitch motion of the blades.

8. The method of claim 7 , wherein step (d) comprises indexing the rotating portion of the swashplate assembly so that one end of the pitch link trails the opposite end of the pitch link in one indexed position and leads the opposite end in another indexed position.

9. The method of claim 7 , wherein step (d) comprises indexing the rotating portion of the swashplate assembly to prevent contact of the pitch link with the yoke during operation.

10. The method of claim 7 , wherein step (d) comprises selectively indexing the rotating portion of the swashplate assembly to cause rotation of each pitch link between an orientation that is substantially parallel to the mast axis and an orientation inclined relative to the mast axis.

11. An aircraft having a blade-pitch control system for controlling a pitch angle of each of a plurality of blades on an aircraft rotor, the blades being rotatably connected to a yoke for rotation with a rotor mast, the control system comprising:

a swashplate assembly having a non-rotating portion and a rotating portion;

an indexing portion of the mast, the swashplate assembly being translatably affixed to the indexing portion;

a pitch link connecting the rotating portion of the swashplate assembly to each blade;

wherein translation of the swashplate assembly along the indexing portion causes a change in pitch of the blades and a corresponding indexing of the rotating portion of the swashplate assembly relative to the mast, the indexing causing a change in an angular orientation of each pitch link, thus providing for selected pitch-flap coupling between flapping motion of the yoke and pitch motion of the blades; and

wherein the indexing portion comprises curved splines connected to and causing indexing of the rotating portion of the swashplate.

12. The aircraft of claim 11 , wherein the curved splines are helical in shape.

13. The aircraft of claim 11 , wherein the curved splines have a non-constant curvature.

14. The aircraft of claim 11 , wherein an end of each pitch link connected to the rotating portion of the swashplate assembly trails the opposite end of the pitch link in one indexed position and leads the opposite end in another indexed position.

15. The aircraft of claim 11 , wherein indexing of the rotating portion of the swashplate assembly prevents contact of the pitch link with the yoke during operation.

16. The aircraft of claim 11 , wherein indexing of the rotating portion of the swashplate assembly causes selective rotation of each pitch link between an orientation that is substantially parallel to the mast axis and an orientation inclined relative to the mast axis.