Zenith Aircraft Builders and Flyers
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Rod end retaining
I recently received a photo of a friend’s aircraft autopilot system and saw large penny washers over the face of the rod ends. As we know Zenith don’t agree that the rod ends can separate from the entrapped ball and bolt to the adjacent structure, but I am at the point where I could install them if I choose. The waters get muddied when EAA encourage their use, as detailed in attached photo. I have a couple of questions for the group:
1) I can only imagine that at some point in the past there has been a failure, but if there had been I would expect it is an industry standard to use a retaining washer, so does anyone know of such a failure?
2) Can someone explain how an entrapped ball can separate from the circular collar cage, and how did they make those suckers in the first place?
The standard AN970 washers are 1”, but you actually need the 3/4” ones in my view. Like everything Zenith if you decide to go down this path you often have to change the AN? bolt length to accommodate the extra length, and my local supplier has minimum quantity orders, generally 20, so I frequently have 16-18 spare.
3) Has anyone else gone down this path and would be happy to discuss either on or off list?
Thanks.
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IMG_7877.jpeg, 894 KB
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Replies to This Discussion
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Permalink Reply by John Austin on
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Although Zenith doesn't specify in their plans the use of large washers on Heim joints (at least not on my plans from years ago), I'm not aware of any objection by Zenith to this. I've never heard of one of these joints separating, but I recall reading "somewhere" on the internet that it has indeed happened at least once? Seems to me the joint would have to be extremely contaminated with grit to wear that badly and should be caught on an annual inspection long before it gets that loose!
About the only downside I can think of is to be sure that if the control rod is slightly off-axis and not perpendicular to the shaft or bolt, the joint might require a spacer between the ball and the washer to ensure full freedom of movement.
John
N750A
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Permalink Reply by Tony Renshaw on
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Hi John,
Sorry its taken a while to get back to you on this, and thanks for replying. The washers have a mating surface that is the same size as the ball in a rod end, so they have thought of everything.
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Permalink Reply by Gary Welch on
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Defects happen. A penny washer could literally save your life. I don't see any questions here.
No issue using a stainless steel washer here. No need for AN.
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Permalink Reply by Jim and Amelia Isaacs on
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A search of AC 43.13 for “rod end bearing” produces precious few results, none of which discuss an oversized safety washer. To me, and acknowledging if it makes you feel safer, then do what you want, but the only relevant mention I found to this discussion is “Cracks and subsequent failures of rod ends usually begin at the thread end near the bearing and adjacent to or under the jam nut. (See Figure 9-5.)”
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Permalink Reply by Dave Blackburn on
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Go to Pegasus Auto online and buy Rod End Safety Training washers. Up size your AN bolt to give at least 3 threads on the nylon lock nut. Changed all 8 rod end bearing. These washers allow axial deflection of the bearing because they are angled away from the bearing. I have had bearing separation during flight in the Air Force. A training washer allowed for safe landing.
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Sorry spell check Retaining Washer not Training
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