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  #21  
Old 03-17-2014, 06:35 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 543
Default 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!
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  #22  
Old 09-29-2017, 05:00 AM
tgmillso tgmillso is offline
 
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 447
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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.
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-...utter-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.
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  #23  
Old 09-29-2017, 05:59 AM
BillL BillL is online now
 
Join Date: Sep 2007
Location: Central IL
Posts: 3,941
Default

Quote:
Originally Posted by tgmillso View Post
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.
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-...utter-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.
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  #24  
Old 09-29-2017, 07:35 AM
AlexPeterson's Avatar
AlexPeterson AlexPeterson is offline
 
Join Date: Sep 2005
Location: Maple Grove, MN
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Quote:
Originally Posted by az_gila View Post
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.
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  #25  
Old 09-29-2017, 05:00 PM
tgmillso tgmillso is offline
 
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Location: Launceston, Tasmania, Australia
Posts: 447
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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.
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  #26  
Old 09-29-2017, 10:29 PM
tgmillso tgmillso is offline
 
Join Date: Nov 2012
Location: Launceston, Tasmania, Australia
Posts: 447
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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.
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  #27  
Old 09-30-2017, 07:26 AM
bpattonsoa bpattonsoa is offline
 
Join Date: Apr 2005
Location: Indepenence, Oregon
Posts: 257
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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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