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08-15-2018, 07:23 AM
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Join Date: Dec 2010
Location: Culpeper, VA
Posts: 693
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Quote:
Originally Posted by BobTurner
I believe the root cause here may be a subtle but important deviation from the instructions. You state the safety wire was being held by being compressed in the [rod end] assembly.
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I don't think there was any real compression. That was just conjecture in the original post because the break wasn't seen until I started moving the nut. It's possible but it's hard to imagine how it could actually be compressed. It may have just been the "springy-ness" of the wire holding it in place.
I dug up some old pics of the build. The root cause is that I routed the safety wire perilously close to the top of the tube. There was no interference at that point but it's not hard to imagine after a lot of vibration that the "loop" inside the tube changed position and along with the normal few degrees of play in the bearings that it worked itself over the top.
I share this picture as an example of how not to do it. The wire is too tightly wound and it's routed too much "over the top". I don't know why I did it that way and not just along the left side. Also the nut looks like it's not as much on the flat as the plans say, but the weird angle might make it look worse than it is. I know there was no interference at the start, but you can see that with a little shifting of the wire working out of the hole at the top (and in at the bottom), etc, and the normal play in the bearings we could get the problem I found.
This, I'm sure, is what caused the problem.
__________________
-Joe Wilbur (N520LW)
Phase II - 11/2017
First flight - 8/2017
RV-10 Build Log
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08-15-2018, 08:51 AM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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That?s a good photo of the issue, and I agree with you. If the plans say the tolerance there is so tight that you need the nut?s flat up, you don?t want anything (like safety wire) above the nut either.
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08-15-2018, 09:46 AM
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Join Date: Jan 2009
Location: Salt Lake City, Utah
Posts: 554
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Safety wire break
I found my safety wire broke during my condition inspection and reported it on VAF. I did a better job getting the wire away from the rotating/moving parts and have had no further problems.
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A&P RV-10 Flying 1000+ hours
SuperSTOL Flying 170 hours
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08-15-2018, 11:51 AM
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Join Date: Feb 2005
Location: Wisconsin
Posts: 612
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Scott, you probably are correct on the Vegas one. I heard it second hand, and could absolutely have heard it incorrectly. I wish I could remember more details right now on the other one. It's probably been 3 - 5 years since the discussion. Time flies by so quick, it's hard to believe I've already put over 12 years on my -10. If I find it, I'll pass it on.
That said, I do have an idea for a permanent fix if someone wanted to think it though. Picture a T-shaped strap that goes on the bottom of the pushrod tube, riveted on. Maybe about .030-.040 thick. It comes forward as a strap, under the rod end and threads, and up by the whole connection point you have the ears of the T, that get folded up and bolted between the rod end and the other control mechanism, basically right where the safety wire sits today. The issue I see is that there would have to be enough gap for this thing to act as a bushing, but if there were a way to get it in there, it could prevent the tube from ever rotating at all. It could be done on either end of the tube, so long as the tube is never allowed to rotate. Anyway, that's just thinking out loud.
Last edited by TimO : 08-15-2018 at 11:55 AM.
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08-16-2018, 10:14 AM
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Join Date: Dec 2014
Location: Just Minutes from KBVI!
Posts: 1,039
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Does no one make a rod end with a longer threaded length that could be used in this application?
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08-16-2018, 10:17 AM
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Join Date: Dec 2010
Location: Culpeper, VA
Posts: 693
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Quote:
Originally Posted by 1001001
Does no one make a rod end with a longer threaded length that could be used in this application?
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It's not just the length of the threads that matter. It can't be allowed to turn at all or the push tube may become the new elevator stop.
__________________
-Joe Wilbur (N520LW)
Phase II - 11/2017
First flight - 8/2017
RV-10 Build Log
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08-16-2018, 12:16 PM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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Spacers?
Quote:
Originally Posted by jwilbur
It's not just the length of the threads that matter. It can't be allowed to turn at all or the push tube may become the new elevator stop.
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One solution to prevent a disaster if the tube did rotate would be to make custom length thin walled tube spacers over the exposed rod end threads.
Cut to length after the push rod is adjusted for final length and do it at both ends.
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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08-16-2018, 01:03 PM
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Join Date: Mar 2006
Location: Newport, TN
Posts: 7,496
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Quote:
Originally Posted by az_gila
One solution to prevent a disaster if the tube did rotate would be to make custom length thin walled tube spacers over the exposed rod end threads.
Cut to length after the push rod is adjusted for final length and do it at both ends.
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Yes, I agree! Can't think of anything more simple and almost fail proof.
Quote:
Originally Posted by Brantel
Not sure what the other end looks like since I don't have my plans yet but if it has no other constraints to prevent it, I would install extra nuts on the other rod end bearing so that the push tube could not physically rotate enough to unscrew that end. I would also consider putting a sleeve on that end between the bearing head and the nut to prevent it from unscrewing the other end as well. A low profile sleeve should clear F-1065 if the nut does.
It is hard to tell from the photo, but it also looks like the safety wire was twisted a bit tight. AC 43.13 states 6-8 twist per inch are acceptable.
Glad you caught this!
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08-16-2018, 06:01 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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Quote:
Originally Posted by az_gila
One solution to prevent a disaster if the tube did rotate would be to make custom length thin walled tube spacers over the exposed rod end threads.
Cut to length after the push rod is adjusted for final length and do it at both ends.
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+2
I was thinking of this too. Just not sure I can get thin walled tubing thin enough to fit inside the clevis fitting but thick enough to not crack.
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08-16-2018, 06:49 PM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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Quote:
Originally Posted by BobTurner
+2
I was thinking of this too. Just not sure I can get thin walled tubing thin enough to fit inside the clevis fitting but thick enough to not crack.
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1/16" wall tubing should be OK and would be of a lesser diameter than the jam nuts.
It does not need to be torqued against - I was actually thinking of the spacer being a little loose. It's just there to prevent the push rod from turning (a lot) and letting a rod end fall out, the "disaster scenario".
But I'm not sure what you mean when you say "fit inside the clevis fitting".
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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