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Discouraged?Rudder Binding

Michael Burbidge

Well Known Member
I spent the first full day after moving to the hangar yesterday trying to accomplish one thing: mount the rudder. I thought it would take me an hour at most. It turns out I spent the whole day on it and still don't have a completely free moving rudder.

I had followed the directions when mounting the HS many months ago to make sure the brackets on the stab are aligned. I can run a straight edge along them and they are in line. I had also followed the measurement for the rod end bearings in the directions as starting point. The space between the rudder and the HS at the top is parallel.

I'm to the point where bolts can be dropped into each bearing easily. So that tells me the bearings are aligned with the brackets. Getting the bearings into the brackets is a wrestle.

After installing all three bolts and tightening them down, the rudder does not swing freely. I tried lots of stuff.

I have determined that the top two nuts can be tightened and the rudder swings freely. But as soon as I put the last little tightening twist on the bottom nut, it no longer swings freely.

I removed the center bolt, and have the same problem between the top and bottom bolts. With just the top and bottom bolts installed and nuts tightened, it does not swing freely.

I found that by putting a thin washer in the following two places, it almost eliminates the drag, but not quite. 1) Top rod bearing - between the top half bracket and the rod end bearing 2) Bottom rod bearing - between the bottom half bracket and the rod end bearing.

It seems like the problem is with the bottom bearing. I can hear the bottom bearing make a slight noise as the rudder stops swinging, going from dynamic friction to static friction that stops it.

Is it possible that the bearing is bad. I can move the ball smoothly with my hand.

I'm very discouraged and not sure what to try next. I was going to order a spacer from McMaster's just a little bigger than a thin washer and see if it gets better with that in the place of the thin washers.

Suggestions welcomed!
Michael-
 
Don't be discouraged. You have come a long way. If I read your post correctly, bolts drop in nicely, or with a little persuasion. But once tightened your feeling binding? Have you tried any LPS bearing lubricant? Are the receivers parallel to the bearing? Its not unusual to have to tweak these a bit. You can also grease them.
Nice video here.
http://www.eaavideo.org/video.aspx?v=1628410977001
 
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Not aligned or rivet heads

I had two similar issues with initial control surface fitting:

1. Brackets for bearings aren't truly aligned. Dimensions to adjust rod bearings in plans are the starting point. I'd adjust the bottom bearing 1/2 turn inward and re-tighten. If that doesn't fix it, try another 1/2 turn. Still not fixed, then return to start and try 1/2 turn and/or full turn out. Don't back it out so far that minimum threads aren't engaged.

2. After paint, I got resistance at full deflection which ended up being nose of surface rubbing on rivet heads in stab. Backed all bearings out 1/2 turn to remain aligned but further from stab and problem gone. (trying to flex the nose into a more round shape to clear rivets didn't help in my case).

Good luck
 
Try this simple test first.

Shine a flashlight upwards from the bottom hinge through the three holes as you look down through the top hinge hole. You will soon see how well aligned the holes are.

Do this separately on both the rudder and the fin hinge holes.
 
The rudder hinge brackets on my RV-7 vertical stab have a slight fore/aft misalignment as built, but there is still some flexibility in the lower end of the main spar where it will attach to the fuselage. My plan is to bolt the rear spar to the fuselage, then center a tight nylon thread in the end brackets, and flex the spar fore/aft until the thread centers in the center bracket. Then clamp the forward VS attach in that position and drill.
 
Back to basics:

If the bolts all drop in, and the rudder swings freely, then the basic geomety is correct. After you tighten down on the ball and force it to rotate (do its job), then you have a problem? Then you have a partially locked ball. With the rudder off, can you swivel/rotate the ball by hand? If not, you have corrosion, hardened preservative, or a failed ball.

Any chance you simply stuck a bolt or screwdriver through the ball like a "T handle" when you screwed the rod end in the first time? if so, there's a good chance you dinged the races and locked it up.
 
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Couple of things ...

First , I assume you're checking the counterweight at the top of the rudder, to assure it's perfectly parallel to the top of the HS. That's a pretty close fit when aligned correctly; it bears close watch.
Second, another good check on your bearing and pivot bracket alignment is to drop a string down through. Any misalignment shows up in a hurry. That simple check helped me a ton at that phase.
 
More info...

The ball moves freely. I bought the tool from Avery for tightening rod ends. So I did not use a screw driver. I have put a straight edge to the brackets. Bolts drop in to the bracket/bearing with almost no persuasion.

The counterweight at the top is parallel to the top of the HS, at least by sight. I will measure with a ruler just to be sure.

I will try the string through both the brackets and rod ends, and I will try some grease on the rod end bearing.

Thanks for the tips,
Michael-
 
Back to basics:

If the bolts all drop in, and the rudder swings freely, then the basic geometry is correct. After you tighten down on the ball and force it to rotate (do its job), then you have a problem? Then you have a partially locked ball.

Or, the action of tightening the nut is distorting something in the mounting brackets.

I would check the ball free motion first, easier to do. If that is not the problem, try tightening one nut only------see if it still moves easy. Then try backing that nut off a bit, and try another ETC. If that doesnt find the issue, try again, but leave the first nut tight.

You are really close, just need to find and eliminate this gremlin.
 
The ball moves freely. I bought the tool from Avery for tightening rod ends. So I did not use a screw driver. I have put a straight edge to the brackets. Bolts drop in to the bracket/bearing with almost no persuasion.

....-

Another easy alignment check -

Drop in the upper and lower bolts - move the rudder hard over left or right - see if the middle bolt will still drop in with the deflected rudder.
 
another easy check

Hey Mike:

You say the bolts drop in easily with the rudder in trail. Try turning the rudder to full lock and check if they will still move freely. If not, you have a pivot axis alignment problem. If they are still free, then you have a rod end ball stuck, or you have a vertical alignment problem with one of your pivots. Since the rod end ball can tolerate some degree of misalignment, you can tweak the steel brackets on the fin spar up or down to get things 'just so'.

If you have a rod end that doesn't want to turn as required, try washing it out and re-greasing it. I have found more than one brand new frozen bearing in my inventory!

Carry on!
Mark
 
Or, the action of tightening the nut is distorting something in the mounting brackets...

Possible, but those steel mount brackets move around a whole lot without much complaint. I've seen them deflected out of plane by an eigth inch or more (visable Z bend), yet with no binding.

As many have pointed out, doing the top and bottom only, and seeing if the middle bolt will still drop in at all deflection angles will tell the tale of alignment, but it seems the thing locks up right away, which seems to point toward a tight ball.

This situation is a strange thing though :confused:
 
If the rudder swings freely with all the bolts installed and no nuts, I suspect it is not alignment. This narrows it to a bad bearing, or more likely a pinching of the rod end. Are the ears of the bracket parallel when the bolt is tightened, or bent slightly inward? With the bottom nut tightened, move the rudder, and look for interference between rod end (other than the bushing itself) and the bracket structure. If you see any interference, add washers between the bushing and bracket, to eliminate this interference, and drive the bracket to be parallel.

Aaron
 
Good point. The rod end should contact the hinge bracket ears on the ball ONLY.
 
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Try these...

I'm not going to get back to the hangar until tomorrow night. But I will try all these suggestions to diagnose the problem, and report the results.

Thanks much!
 
To kick off an old post again, I too am having issues with rudder binding, but in my -7.
My VS hinge line axis is dead on, as are my rod end bearings, and I confirmed this by having all the bolts drop through easily. Only once I tightened up the bolts the friction occurred. I suspected the issue was misalignment between the hinge flange locations in the vertical directions, and progressively undid each bolt at a time to see if there was any spacing between the steel brackets and the rod end bearing eye. Sure enough, with the top two bolts tight but the lower bolt loose, there was a gap between the rod end bearing and the lower flange at this location. This gap was approximately 0.016", so I first stuffed a AN960-416L (0.032") washer in the gap, did the bolt back up and the result was good (the binding torque had halved to approximately 18in lb) but not spectacular. I then fabricated an 0.016" shim, removed the 0.032" washer and installed this shim in its place, thinking that I must have gone too far the other way. With the bolt tightened again, the binding increased back to it's original 36in lb value. :confused:
At this point I had to throw in the towel for the day, but I guess my question is, what is considered to be an acceptable binding torque? I'd heard before that control surface binding may contribute to flutter, then I discovered this Tony Bingelis article which essentially states the opposite (to a degree).
https://www.eaa.org/en/eaa/aviation...al-operation/control-surface-flutter-problems
I'd also take any suggestions on a better way to tackle this friction issue rather than my time consuming trial and error approach (and yes, my rod end bearings are cleaned and lubricated)...
Thanks.
Tom.
 
To kick off an old post again, I too am having issues with rudder binding, but in my -7.
My VS hinge line axis is dead on, as are my rod end bearings, and I confirmed this by having all the bolts drop through easily. Only once I tightened up the bolts the friction occurred. I suspected the issue was misalignment between the hinge flange locations in the vertical directions, and progressively undid each bolt at a time to see if there was any spacing between the steel brackets and the rod end bearing eye. Sure enough, with the top two bolts tight but the lower bolt loose, there was a gap between the rod end bearing and the lower flange at this location. This gap was approximately 0.016", so I first stuffed a AN960-416L (0.032") washer in the gap, did the bolt back up and the result was good (the binding torque had halved to approximately 18in lb) but not spectacular. I then fabricated an 0.016" shim, removed the 0.032" washer and installed this shim in its place, thinking that I must have gone too far the other way. With the bolt tightened again, the binding increased back to it's original 36in lb value. :confused:
At this point I had to throw in the towel for the day, but I guess my question is, what is considered to be an acceptable binding torque? I'd heard before that control surface binding may contribute to flutter, then I discovered this Tony Bingelis article which essentially states the opposite (to a degree).
https://www.eaa.org/en/eaa/aviation...al-operation/control-surface-flutter-problems
I'd also take any suggestions on a better way to tackle this friction issue rather than my time consuming trial and error approach (and yes, my rod end bearings are cleaned and lubricated)...
Thanks.
Tom.

Tom, I recently had this very issue on one elevator, unfortunately my rudder had/has a tweak of friction that is due to misalignment - but back to yours. If the bolts drop in and friction occurs only when tightening them, it is axial displacement, not pivot axis alignment. Do like the op and tighten or loosen one at a time until you find the offending bearing. Leave the other two pivot bolts tight. Assuming you have cleaned and lubed each bearing, then with the offender loose (bolt in place), take a feeler gage and measure the gap between the helm bearing and the steel tab. Then you know which tab is off and what direction. Remove the rudder, measure the gap precisely (.001"), bend the tab by hand until the gap is equal to the helm ball width. Reassemble and marvel. It might take a couple of times but that should solve your problem. Again assuming the fishing line test on alignment passed on both rudder and VS.

Let us know how that works.
 
Another easy alignment check -

Drop in the upper and lower bolts - move the rudder hard over left or right - see if the middle bolt will still drop in with the deflected rudder.

This is a key point!

That the bolts drop in when the surface is in trail does not mean the three are aligned in a straight line.

As an exaggerated example, if the middle one (or any of the three) were 1/2" back from alignment with the other two, but the mating rod end were also 1/2" back from alignment, the bolts will still drop in. But, as soon as the surface were deflected binding would occur.

A string or similar is the only good way to verify alignment. I used fishing line, and carefully tightened it at four clock positions on each end. It should show no gaps at any of the 4 positions on the middle holes.
 
Thanks Alex and Bill. When I initially set my rod end bearings and the hinge line, I used a schrader valve cap with a hole drilled in the middle and a fine fishing line pulled tight, so I'm confident I have this axis lined up. As soon as I tighten that bottom bolt, the friction is the same in all positions of the arc, so I'm leaning toward the fact that it's the positioning of the hinges in the vertical sense. I'm about to head back over to the hangar and have one last shot at this, so I'll let you know how it goes.
Tom.
 
This seems to be one of those rare cases in aeroplane building where doing too much is the right thing to do. Before proceeding with any bracket bending, I decided to wedge in a full size washer in place of the AN960-416L, and sure enough there was absolutely no binding. Thus I decided to so I created a lever out of pine that was 7/16" thick, about 1.5" wide and 6 inches long, then with the rudder removed, wedged it in between the two hinge brackets and bent the top one upwards by 1/16" (the thickness of a 416 washer). I then pivoted the lever off the custom tail light wire bracket I have fabricated that mounts across between the two AN4 bolts that hold the VS in place, and used this to lever the bottom bracket upwards the same 1/16". I put the rudder in place now without any additional washers, tightened things up, but was unfortunately still getting binding, this time about 12in lb. Thinking I must have gone too far, I wedged a 416L washer between the top of the bearing eye and the top bracket, but this only made things worse. I then removed this and placed it underneath the bearing eye, and sure enough, problem solved and essentially zero binding. Rather than risking over bending things, I decided to settle on what I had and torqued things up as is.
Thanks for you pointers.
Tom.
 
I have always checked the brackets bend before riveting them on. Sometimes the bend has not been right on 90 degrees. It is a simple fix beforehand.

Several of the brackets on the -10 were off a bit. You can check them when on the spar by using a good square and a spacer to get the square over the rivets.
 
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