Rudder Cable Catching on Flap Actuator

I am presently doing a periodic inspection on my 9A and have found that at some time the right side rudder cable has snagged on the bolt that goes through the flap weldment actuator arm as evidenced by the slightly distorted cable in the photo below. Also the cable is slightly "polished" in this area indicating that it has rubbed along the bolt/nut.

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I was easily able to replicate this by hitching the cable over the nut/bolt and the cable would stay in place with the rudder pedals being moved.

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Firstly I'll admit I have contributed to this as I had installed the bolt in the opposite direction to the plans. The plans show the bolt head on the outboard side of the flap actuator arm and in this configuration it would be much less likely that the cable would snag on the thinner bolt head. I also used the smaller MS21042 nut rather than the AN365 nut specified in the plans but I can't see this being a contributing factor.

I suspect that many RVs would have the bolt direction wrong as it is impossible to install the bolt from the outboard side once the flap actuator weldment is installed in the fuselage (at least in my 9A). I have now installed the bolts in the correct direction. This involved disconnecting the flaps and undoing the three nylon mounting blocks so I was then able to move the weldment just enough to install the bolts.

I am not quite sure how the cable actually got distorted. I suspect that I lowered the flaps (on the ground) when the cable had snagged on the bolt and this took all the slack and slightly "bent" the cable. This could not have happened in the air as I would have noticed right rudder being applied and the aircraft yawing as the flaps were lowered.



Fin
9A

Make a short U channel of thin aluminum and rivet it to the skin over the flap actuator. Hang the rudder cable in it and your troubles are over. Make sure the leg of the U that goes against the skin is longer so 1) you can buck the rivets and 2) the rivet tails are not rubbing the rudder cable. You could alternatively make grommet guides or split-nylon block guides but the aluminum hangers work well.

flion said:

Make a short U channel of thin aluminum and rivet it to the skin over the flap actuator. Hang the rudder cable in it and your troubles are over. Make sure the leg of the U that goes against the skin is longer so 1) you can buck the rivets and 2) the rivet tails are not rubbing the rudder cable. You could alternatively make grommet guides or split-nylon block guides but the aluminum hangers work well.

Click to expand...

Only do this, if you can rivet it around the weldment. Do not drill holes in that weldment as you will weaken it.

You can make a "U" and pass the bolt through the bottom of the "U" so it will guide the cable up and over the bolt head. Just remember to make some tabs on the "U" so it won't turn and catch the cable.

I do have my bolts in the proper orientation and my cable does not appear to have snagged that bolt head.

Just attach a guard on your cover.

Good observation, Finley.

One other possible solution: rivet a small piece of aluminum to the fuselage side (near the actuator) to hold another set of double grommets like those called out for where the rudder cables go through the bulkheads. That would keep the cable up and away from the actuator even when there might be some slack.

Yes, Steve, that's what I meant by grommet guides. Van uses them in the RV-10 in the tunnel. I'm not sure I understand what Bill is saying, especially in regards to my earlier post. Nowhere do I say to drill or attach anything to any weldments. The U-channels act as hangers and are above the flap, in line with the desired cable route and attached to the skin. Attached to the inner access panel also works but is not my preference, as I like to be sure the cables are in position before I put the panels on.

You could also use a section of large diameter poly tube like used at the cable exit (or split a length of small diameter tube) and route it between the existing bulheads to support the cable. You could also add a bit of angle and a cushion clamp midway for additional support.

Ok, being the wise guy I thought I was, , I remembered reading about this 'bolt in backwards' thing. So I disconnected the actuator weldment as Fin described above and put the hardware in per the plans along with the linkage. I went through this the first time eons ago I'm sure. I now have wings on and am rigging the ailerons, flaps, etc.
So now, if I want to go through the iterations of adjusting the length of the linkage, I have to either:

a. take the weldment loose and put the bolt in backwards while I go through this adjustment process. Then once I'm satisfied with the adjustment, take it all apart and put the bolt in per plans.
OR
b. leave the bolt in backwards and figure out some rig to prevent cable from hanging up. (I am soooo tired of doing work-arounds at this point.)
OR
c. keep the bolt in per plans and screw & un-screw the bearing where it connects at the flap end. This may not even be possible, would probably take a long time, and risk screwing up threads on one or the other. Not a good idea.

I MUST be missing something! Someone, please tell me what it is.

TX7A said:

Ok, being the wise guy I thought I was, , I remembered reading about this 'bolt in backwards' thing. So I disconnected the actuator weldment as Fin described above and put the hardware in per the plans along with the linkage. I went through this the first time eons ago I'm sure. I now have wings on and am rigging the ailerons, flaps, etc.
So now, if I want to go through the iterations of adjusting the length of the linkage, I have to either:

a. take the weldment loose and put the bolt in backwards while I go through this adjustment process. Then once I'm satisfied with the adjustment, take it all apart and put the bolt in per plans.
OR
b. leave the bolt in backwards and figure out some rig to prevent cable from hanging up. (I am soooo tired of doing work-arounds at this point.)
OR
c. keep the bolt in per plans and screw & un-screw the bearing where it connects at the flap end. This may not even be possible, would probably take a long time, and risk screwing up threads on one or the other. Not a good idea.

I MUST be missing something! Someone, please tell me what it is.

Click to expand...

Since disconnecting the push rod from the upper end allowed you to adjust the length of the push-rod, disconnecting it at the bottom (flap) gives you the same capability.

rvbuilder2002 said:

Since disconnecting the push rod from the upper end allowed you to adjust the length of the push-rod, disconnecting it at the bottom (flap) gives you the same capability.

Click to expand...

Ok, so you're saying my choice "c"?
I'll give it a try.

A simple Z bracket riveted to the cover over the highest travel of the arm and fits so it just presses on the skin will keep the cable form getting snagged by the bolt head or end.

rvbuilder2002 said:

Since disconnecting the push rod from the upper end allowed you to adjust the length of the push-rod, disconnecting it at the bottom (flap) gives you the same capability.

Click to expand...

You are right about option "C" in one way but possibly not in practice.

The bottom bearing is screwed into a nutplate and has to be done with a wrench at the base of the studded bearing. Very time consuming since the flap skins are in the way for a good purchase with the wrench. If the hole in the fuselage is done well, the bearing will NOT go into the fuselage unless this stud is screwed all the way in. In my case, I cannot remove that bearing without disconnecting the top bearing because the flap rod will hit the side of the fuselage hole as the flap bearing is backed out. Yes, there is plenty of operational clearance. Even if I could remove the flap bearing by itself, I for one would not want to go through that much work or for that matter wear out the nutplate via multiple bearing installations before first flight.

The top connection is with a through bolt that does not even need a nut during the adjustment process in order to be geometrically correct.

It would be easier to do all the adjustment with the top disconnected (which I did) and when done, do the necessary disassembly to reverse the top bolts if one feels it is necessary (which I did not do)

Now I'm really confused if the answer is "C".

You can't remove the bearing from the flap without disconnecting the pushrod at the top end, right?

Finley Atherton said:

Firstly I'll admit I have contributed to this as I had installed the bolt in the opposite direction to the plans.

...

I have now installed the bolts in the correct direction.

...

Other suggestions welcome.

Click to expand...

My suggestion: Now that you've identified and corrected the root cause of the problem, i'd suggest you don't need to do anything else but monitor it for a while until you're comfortable that the problem is resolved.

Another simple fix that I used is return springs attached from each of the rudder pedals to the firewall. The purpose is to keep tension on the cables at all times. It also helps with wind damage to the rudder.

Go to your nearest West Marine and get some of these split cable covers.
You can slide them over the rudder cables and these will protect and support the cables where they are passing by the flap weldment.