Poor Stick Rigging

[DanH]

Well known in some circles, but probably worth illustration...

Subject is the stick assembly for the 6, 7, and 9, specifically where it connects to the forward pushrod. See below

The up elevator limit stop is at the rear of the fuselage; the WD-605 elevator horns should contact F-712D. There should be no binding or springiness as the stick nears full aft, just free motion until the horns hit the 712 with a nice firm clunk.

No clunk, or a springy feeling at full aft? Look back, visually center the elevators, then look at the stick. Is it vertical, or leaning forward?

It should be leaning forward. If not, the built in angles result in the rod end shank binding against the top of the weldment fork; see below. That puts a bending load on the pushrod assembly, notably the AN490 threaded rod end.

Here's a trick which may help the rigging process. Cut a strip of paper about 8 inches long and 1/4" wide. Slip an end into the space above the rod end and move the stick full aft until the elevator horns hit the stop. Now try to pull the paper out of the joint. If it's not free, the joint is binding as below.
.

 

[planenutz]

Great info. I've not seen that before on any of the machines I've had anything to do with, so good to be aware of it. Thanks Dan.

With the stick around the wrong way it must get close to the instrument panel, especially if the stick is the original length. Does it contact the panel?

 

[AlexPeterson]

I recall having to grind just a little from the location of interest - this was something around 25 years ago... I was not able to find any adjustment scenario that would work through the full range of motion.

On the topic of rigging - I've seen this many times: With the stick fully at the four corners, it is very common to see torsional jamming on the aileron pushrods (those going laterally out to the bellcranks). There are only a few degrees of correct angular adjustment between the inner and outer rod ends of these pushrods. During adjustment of them, the torqueing of the lock nuts on them tends to turn them slightly, so some trial and error is required.

How to test for this problem: Hold the stick fully at each of the four corners, and verify that the pushrods can still be rotated slightly. If not, the rod ends are torsionally binding.

 

[lr172]

Great info. I've not seen that before on any of the machines I've had anything to do with, so good to be aware of it. Thanks Dan.

With the stick around the wrong way it must get close to the instrument panel, especially if the stick is the original length. Does it contact the panel?

Surprised we don't find more, as it gets pretty close. When I did the final rigging I watched that, as it seemed like it could easilly bind. Mine was pretty close after the final rigging. I also had someone move the stick and be sure I heard noise from the horn hitting the stop.

 

[PaulvS]

Design of the control column fork

I also needed to grind off a bit of welding "dribble" so that the rod end would not bind in the fork. This was during initial installation, before setting the elevator stops, with the stick back and the lower part of the control column almost touching the spar bulkhead (per the construction manual).
At the time I thought that the fork should have been designed to be 1/16" deeper.

 

[Toobuilder]

Its also noteworthy that the tandems suffer a similar anomaly in the rigging of the intermediate push/pull rod. If the rod ends are not perfectly aligned, they will bind in at full right or full left stick. Again, look for a hard "thunk" at both extremes. Any springiness just before the stop is often indicative of rod end bind. I have corrected this condition of several -4, -8 and Rockets.