ROTOR HUB AND BLADE FOLDING SYSTEM

• US 3,625,631 A
• Filed: 11/03/1969
• Issued: 12/07/1971
• Est. Priority Date: 11/03/1969
• Status: Expired due to Term

• Current Assignee: Bell Helicopter Textron Incorporated (Textron Inc)
• Original Assignee: Cecil Edward Jr. Covington, Martin Harrison Lufkin, Wesley Louis Cresap
• Inventors: Covington, Cecil Edward Jr., Lufkin, Martin Harrison, Cresap, Wesley Louis
• Primary Examiner(s): Powell, Jr., Everette A.
• Application Number:
  US04/873,351
• Time in Patent Office: 764 Days
• Field of Search: 416/142,143,121,124,1
• US Class Current: 416/1
• CPC Class Codes: B64C 27/50 Blades foldable to facilitate stowage of aircraft

Abstract

A system for folding a first pair of rotor blades with a second pair of rotor blades in rotary wing aircraft. Each pair of rotor blades is attached to a separate hub arrangement. The first hub is fixed to the mast for rotation therewith in the normal fashion. A second hub is mounted on the mast and is movable, along splines, up and down the mast from an upper end position to a lower end position. When the second hub is in the upper end position, the second hub is keyed, by virtue of the splines, to the mast for rotation with the mast. Thus, when in the upper end position, the second hub, like the first hub, will rotate with the mast and the rotor blades will rotate in their normal fashion. However, the second hub may be lowered along the splines to the lower end position. When in the lower end position, the second hub is free to rotate relative to the mast. Thus, when the second hub is moved down the mast to the second end position, it may be rotated relative to the first hub to cause the second pair of rotor blades to align or fold with the first pair of rotor blades and reduce the space requirements, transverse to the rotary wing aircraft, for stowage.

Claims

1. A method of folding a first rotor blade assembly movable with and about a drive structure relative to a second rotor blade assembly which is approximately orthogonal to the first rotor blade assembly wherein the second rotor blade assembly is fixed relative to the drive structure comprising the steps of:

a. moving the first rotor blade assembly axially along the drive along the drive structure away from the second rotor blade assembly to a predetermined distance from the second rotor blade assembly, and b. rotating the first rotor blade assembly at the predetermined axial distance from the second rotor blade assembly about the drive structure and relative to the second rotor blade assembly to bring the assemblies into near alignment with each other.

2. A method according to claim 1 further comprising the steps of:

changing the pitch of the rotor blades of the first and second rotor blade assemblies to a maximum in one direction prior to axially moving the first rotor blade assembly away from the second rotor blade assembly, changing the pitch of the blades of the first rotor blade assembly in the opposite direction as the first rotor blade assembly is moved axially away from the second rotor blade assembly, and changing the pitch of the blades of the first rotor blade assembly in the one direction as the first rotor blade assembly is rotated relative to the second rotor blade assembly, whereby the rotor blades of the first and second rotor blade assemblies will nest together as the assemblies are brought into near alignment with each other.

3. In a foldable rotor blade system of the type having a rotor mast, a first rotor blade assembly including a first hub movably mounted on the mast with a first pair of variable pitch blades extending radially therefrom, and a second rotor blade assembly including a second hub fixed to the mast with a second pair of variable pitch blades extending radially therefrom, the improvement comprising:

means for controllably moving the hub of the first rotor blade assembly on the mast relative to the second rotor blade assembly between a first fixed position and a second fixed position, the second position being displaces from the first position both longitudinally and angularly relative to the rotational axis of the mast.

4. The system of claim 3 comprising:

engagement means for securing the hub of the first rotor blade assembly from rotAtion relative to the mast when the first assembly is at the first fixed position.

5. The system of claim 4 wherein the engagement means comprises:

first surfaces fixed to the rotor mast and having components lying in planes that include the axis of the rotor mast and second surfaces fixed to the first hub for mating engagement with the first surfaces when the first assembly is at the first position.

6. The system of claim 5 wherein the moving means comprises:

means for translating the hub of the first rotor blade assembly along the mast between the first position and a third position angularly aligned with the first position and longitudinally aligned with the second position and means for rotating the hub of the first rotor blade assembly around the mast between the third and second positions.

7. The system of claim 6 wherein:

the first surfaces comprise a first set of parallel splines extending longitudinally along a first portion of the periphery of the rotor mast, and the second surfaces comprise a second set of parallel splines extending longitudinally along the interior of the first hub, the first and second set of splines being in mating engagement with each other when the first hub is at the first position and disengaged when the first hub is at the third position.

8. The system of claim 7 wherein the translating means comprises:

screw threads extending along a second portion of the periphery of the rotor mast, the second portion being longitudinally displaced from the first portion in the direction of movement of the first hub from the first to the third position;

a threaded nut rotatably connected to the first hub and surrounding the rotor mast, the threads of the nut engaging the screw threads of the rotor mast for movement therealong when the nut is rotated relative to the mast, the outer periphery of the nut including a set of worm gear teeth; and

a worm having a shaft rotatably connected to the first hub, with the axis of the wormshaft positioned in a plane perpendicular to the axis of the rotor mast for meshing engagement of the worm with the gear teeth of the nut, whereby rotation of the wormshaft causes rotation of the nut relative to the first hub, in turn causing movement of the nut along the screw threads of the rotor mast, in turn causing axial movement of the first hub along the rotor mast between the first and third positions, so long as the first and second set of splines remain in mating engagement with each other.

9. The system of claim 8 wherein the means for rotating the hub of the first rotor blade assembly around the mast between the third and second positions comprises:

first stop means for preventing rotation of the nut relative to the mast when the first and second set of splines disengage at the third position, whereby rotation of the wormshaft, causing rotation of the first hub relative to the nut, results in rotation of the first hub relative to the rotor mast between the third and second positions.

10. The system of claim 9 wherein the first stop means comprises:

a first stop fixed to the threaded nut;

a second stop fixed to the rotor mast for engagement with the first stop when the first hub is at the third position, for preventing rotation of the nut in one direction relative to the rotor mast; and

a third stop movably connected to the rotor mast for selective engagement with the first stop when the first hub is at the second position, for preventing rotation of the nut in an opposite direction relative to the rotor mast, and for selective disengagement form the first stop when the first hub is at the third position.

11. The system of claim 10 comprising:

second stop means for limiting the rotation of the first rotor blade assembly relative to the rotor mast to between the third and second positions.

12. The system of claim 11 wherein the second stop means comprises:

a fourth stop fixed to the hub of the first rotor blade assembly;

A fifth stop fixed to the rotor mast for engagement with the fourth stop when the first rotor blade assembly is at the third position for preventing rotation of the first hub in a direction further away from the second position; and

a sixth stop fixed to the rotor mast for engagement with the fourth stop when the first rotor blade assembly is at the second position for preventing rotation of the first hub in a direction further away from the third position.

13. The system of claim 12 comprising:

means for selectively engaging the third stop with the first stop when the first rotor blade assembly is between the third and second positions.

14. The system of claim 13 wherein:

the third stop comprises a camming member pivotally connected to the rotor mast for movement of a camming surface of the member into and out of engagement with the first stop, and the means for selectively engaging the third stop with the first stop comprises a boundary surface fixed to the hub of the first rotor blade assembly for maintaining the camming surface of the third stop in engagement with the first stop, the boundary surface subtending an angle sufficient to maintain contact with the third stop when the first rotor blade assembly is at or between the second position and a point adjacent the third position

15. The system of claim 14 wherein the angle of engagement contact between the camming surface of the third stop and the first stop is such that pressure of the first stop against the camming surface tends to pivot the third stop out of engagement with the first stop, whereby as the first rotor blade assembly rotates from the second to the third position, the third stop will disengage from the first stop when the boundary surface releases the third stop as the first rotor blade assembly reached the third position.

16. The system of claim 3 wherein:

the first hub comprises a substantially flat midportion facing the second hub and extending in opposite radial directions from the mast and the second hub comprises a substantially flat midportion facing the first hub and extending in opposite radial directions from the mast, said first hub being positioned adjacent the second hub when the first rotor blade assembly is at the first position.

17. The system of claim 16 comprising:

a swashplate surrounding the rotor mast and axially spaced from the first and second rotor blade assemblies, a pair of pitch links for connecting the swashplate to the blades of the first rotor blade assembly, and swivel means at each end of each pitch link to permit each pitch link to swivel about its axis when the first rotor blade assembly is folded to near alignment with the second rotor blade assembly.

18. The system of claim 7 wherein the first hub includes a pair of slots, each slot being positioned along the main axis of the first rotor blade assembly on opposite sides of the mast, the system further comprising:

a pair of U-shaped pitch horns, each pitch horn having a first end connected to the swivel means at one end of one of the pitch links and a second end extending through one of the slots and fixed to a separate rotor blade of the first assembly, with the midportions of the U-shaped pitch horns arranged on the side of the first hub away from the second hub, whereby axial movement of the first rotor blade assembly away from the second rotor blade assembly will permit the pitch horns to rotate about their second ends without contacting the first hub.