Hangar 9 Sukhoi SU-31 Instruction Manual page 23

Step 6. Thread an A-nut (included with swivel clevis) onto each
side of the threaded rod and securely tighten against the rudder.
Step 7. Screw a molded swivel clevis onto each side of the
8-32 threaded rod so that it is tight against the A-nut.
Step 8. Hinge the rudder using the same techniques as with the
aileron and elevator.
Note: You may need to drill out the bottom hinge location
in the rudder using a 5/32" drill bit to allow the
hinge to seat correctly.
Step 9. Screw a 4-40 ball link five to six turns onto a 5" long
4-40 Pro-Link. Screw the opposite end of the linkage into the
swivel control horn that was installed in Step 7. Adjust the length
until the hole in the ball link lines up with the outer hole in the
servo arm when the rudder is in neutral and the arm is centered.
Step 10. Using the 4-40 screws and nuts included in the swivel
control horn package, attach the ball link to the outer hole in the
arm. The correct sequence is 4-40 screw, ball link, servo arm,
and 4-40 nut. Don't use the beveled standoff. Be sure to use
threadlock on the 4-40 screws.
Step 11. Repeat Steps 9 and 10 for the other rudder servo linkage.
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