Compact folding yoke with flexible yoke arms in a folding rotor blade assembly
A folding yoke comprising a center yoke pivotally connected to separate foldable flexible yoke arms permits rotor blade fold about a single through bolt connection inboard of a set of bearings. In use, the compact folded arrangement of the rotor blades reduces folded aircraft dimensions in response to ever increasing restricted storage space parameters.
1. A rotor blade assembly, comprising:
a hub spring operatively connected to a central mast;
a center yoke connected to the hub spring;
a flexible yoke arm pivotally connected to the center yoke at a pivot point providing a first pivot axis;
a bearing connecting the flexible yoke arm to a rotor blade, the bearing positioned on the flexible yoke arm outboard of the pivot point; and
a pitch horn connected to the rotor blade with a releasable pin and with a pivot pin providing a second pivot axis.
2. The rotor blade assembly of claim 1 , wherein the flexible yoke arm is generally parallel with an adjacent flexible yoke arm when the flexible yoke arm is rotated around the pivot point to a folded position.
3. The rotor blade assembly of claim 2 , wherein the flexible yoke arm further comprises:
an inboard end, at the pivot point, including a first tang vertically aligned with a second tang; and
the center yoke is between the first tang and the second tang.
4. The rotor blade assembly of claim 2 , wherein the bearing comprises an inboard beam, housing an inboard bearing, connected to the flexible yoke arm in an oblong opening formed in the flexible yoke arm outboard of the pivot point.
5. The rotor blade assembly of claim 4 , wherein the flexible yoke arm further comprises:
an inboard end, at the pivot point, including a first tang vertically aligned with a second tang; and
the center yoke is between the first tang and the second tang.
6. The rotor blade assembly of claim 2 , wherein flexible yoke arm comprises:
a longitudinal axis;
an outboard end connected to the rotor blade in a first attachment plane; and
an inboard end pivotally connected to the center yoke in a second attachment plane, wherein upon rotation of the rotor blade about the longitudinal axis, the flexible yoke arm twists and an angle between the first attachment plane and the second attachment plane is altered.
7. The rotor blade assembly of claim 1 , wherein the flexible yoke arm further comprises:
an inboard end, at the pivot point, including a first tang vertically aligned with a second tang; and
the center yoke is between the first tang and the second tang.
8. The rotor blade assembly of claim 1 , wherein upon removal of the releasable pin and coaxial alignment of the first pivot axis with the second pivot axis, the flexible yoke arm can rotate about the pivot point.
9. The rotor blade assembly of claim 1 , wherein the bearing further comprises:
an inboard beam, housing an inboard bearing, connected to the flexible yoke arm in an oblong opening formed in the flexible yoke arm outboard of the pivot point.
10. The rotor blade assembly of claim 1 , wherein flexible yoke arm further comprises:
a longitudinal axis;
an outboard end connected to the rotor blade in a first attachment plane;
an inboard end pivotally connected to the center yoke in a second attachment plane; and
wherein upon rotation of the rotor blade about the longitudinal axis, the flexible yoke arm twists and an angle between the first attachment plane and the second attachment plane is altered.
11. A method for folding a rotor blade assembly comprising a flexible yoke arm connected to a rotor blade in a first attachment plane and pivotally connected to a center yoke including a first pivot axis in a second attachment plane, a pitch horn connected to the rotor blade at a releasable connection and at a pivotable connection including a second pivot axis, and a bearing connected to the flexible yoke arm outboard of the first pivot axis, the method comprising:
pitching the rotor blade such that an angle between the first attachment plane and the second attachment plane is altered;
releasing the releasable connection; and
rotating the flexible yoke arm about the first pivot axis and the second pivot axis.
12. The method of claim 11 , wherein pitching the rotor blade includes axially aligning the first pivot axis with the second pivot axis.
13. The method of claim 11 , wherein:
the rotor blade assembly is operatively connected to a nacelle pivotally mounted to a wing; and
pivoting the nacelle to a 90° nacelle angle.
14. The method of claim 13 , wherein subsequent to rotating the flexible yoke arm, further comprising, pivoting the nacelle to a 0° nacelle angle.
15. The method of claim 11 , wherein the rotor blade assembly is operatively connected to a nacelle pivotally mounted to a wing, further comprising, pivoting a wing tip of the wing.
16. The method of claim 11 , wherein the rotor blade assembly is mounted to a wing and the wing is mounted to a fuselage, further comprising, subsequent to rotating the flexible yoke arm, swivelling the wing about its vertical axis to align with the fuselage.
17. The method of claim 11 , wherein pitching the rotor blade includes axially aligning the first pivot axis with the second pivot axis
the rotor blade assembly is operatively connected to a nacelle pivotally mounted to a wing; and
further comprising pivoting the nacelle to a 90° nacelle angle.
18. The method of claim 17 , further comprising, subsequent to rotating the flexible yoke arm, pivoting the nacelle to a 0° nacelle angle.
19. The method of claim 11 , wherein pitching the rotor blade includes axially aligning the first pivot axis with the second pivot axis;
the rotor blade assembly is operatively connected to a nacelle pivotally mounted to a wing; and
further comprising pivoting a wing tip of the wing.
20. The method of claim 11 , wherein pitching the rotor blade includes axially aligning the first pivot axis with the second pivot axis;
the rotor blade assembly is mounted to a wing and the wing is mounted to a fuselage; and further comprising, subsequent to rotating the flexible yoke arm, swivelling the wing about its vertical axis to align with the fuselage.