Gimbal lock hook systems for rotorcraft

1. A propulsion assembly for a rotorcraft comprising:

a mast;

a proprotor hub assembly coupled to the mast and having a gimballing degree of freedom relative to the mast, the proprotor hub assembly including a hook receiver; and

a gimbal lock positioned about the mast, the gimbal lock including a locking ring, a gimbal lock hook and an actuation assembly, the actuation assembly configured to raise and lower the locking ring and rotate the gimbal lock hook;

wherein, the gimbal lock is movable between a disengaged position and an engaged position relative to the proprotor hub assembly, the gimbal lock enabling the gimballing degree of freedom in the disengaged position and disabling the gimballing degree of freedom in the engaged position; and

wherein, the gimbal lock hook is hooked to the hook receiver in the engaged position to secure the locking ring to the proprotor hub assembly.

2. The propulsion assembly as recited in claim 1 , wherein the proprotor hub assembly further comprises a gimbal lock receptacle extending from the proprotor hub assembly and adapted to receive the locking ring, the locking ring inserted into the gimbal lock receptacle in the engaged position.

3. The propulsion assembly as recited in claim 1 , wherein the hook receiver further comprises a receiver ring.

4. The propulsion assembly as recited in claim 3 , wherein the receiver ring is rotatable to slidably receive and release the gimbal lock hook.

5. The propulsion assembly as recited in claim 1 , wherein the gimbal lock hook forms a lip protruding radially outward from the mast.

6. The propulsion assembly as recited in claim 1 , wherein the gimbal lock hook and the hook receiver provide a load path between the locking ring and the proprotor hub assembly in the engaged position.

7. The propulsion assembly as recited in claim 1 , wherein the gimbal lock hook is unhooked from the hook receiver in the disengaged position.

8. The propulsion assembly as recited in claim 1 , wherein the actuation assembly has a range of motion including a locking ring axial displacement phase and a gimbal lock hook rotation phase.

9. The propulsion assembly as recited in claim 1 , wherein the actuation assembly further comprises an actuator moveable in a first direction to raise the locking ring and hook the gimbal lock hook to the hook receiver and a second direction to lower the locking ring and unhook the gimbal lock hook from the hook receiver.

10. The propulsion assembly as recited in claim 9 , wherein the actuation assembly further comprises:

an arm having first and second ends, the first end of the arm coupled to the actuator;

a locking ring linkage coupling the second end of the arm to the locking ring; and

a hook linkage subassembly coupling the second end of the arm to the gimbal lock hook.

11. The propulsion assembly as recited in claim 10 , wherein the second end of the arm, the locking ring linkage and the hook linkage subassembly are rotatably coupled at a common revolute joint.

12. The propulsion assembly as recited in claim 10 , wherein the hook linkage subassembly further comprises:

an angle bracket rotatable about a vertex and having first and second ends, the first end of the angle bracket coupled to the second end of the arm; and

a riser having a bottom end coupled to the second end of the angle bracket and a top end coupled to the gimbal lock hook.

13. The propulsion assembly as recited in claim 12 , wherein the vertex of the angle bracket forms an elongated slot permitting the angle bracket to move toward the proprotor hub assembly in response to the locking ring engaging with the proprotor hub assembly.

14. The propulsion assembly as recited in claim 12 , wherein the gimbal lock hook further comprises a leg coupled to the top end of the riser and wherein the gimbal lock hook forms an angle including a vertex coupled to the locking ring.

15. The propulsion assembly as recited in claim 14 , wherein the locking ring, the locking ring linkage and the vertex of the gimbal lock hook are rotatably coupled at a common revolute joint.

16. A tiltrotor aircraft comprising:

a fuselage;

a wing coupled to the fuselage; and

a propulsion assembly rotatably coupled to the wing, the propulsion assembly comprising:

a mast;

a proprotor hub assembly coupled to the mast and having a gimballing degree of freedom relative to the mast, the proprotor hub assembly including first and second hook receivers; and

a gimbal lock positioned about the mast, the gimbal lock including a locking ring and first and second gimbal lock hooks;

wherein, the gimbal lock is movable between a disengaged position and an engaged position relative to the proprotor hub assembly, the gimbal lock enabling the gimballing degree of freedom in the disengaged position and disabling the gimballing degree of freedom in the engaged position; and

wherein, the gimbal lock hooks are hooked to the hook receivers in the engaged position to secure the locking ring to the proprotor hub assembly.

17. The tiltrotor aircraft as recited in claim 16 , wherein the first hook receiver and the first gimbal lock hook are disposed on an opposite side of the mast than the second hook receiver and the second gimbal lock hook.

18. The tiltrotor aircraft as recited in claim 16 , wherein the locking ring fully engages with the proprotor hub assembly prior to the gimbal lock hooks fully hooking to the hook receivers as the gimbal lock moves from the disengaged position to the engaged position.

19. The tiltrotor aircraft as recited in claim 16 , wherein the locking ring further comprises a conical and annular locking ring.