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Question on use of penny washers on control bearings??
I'm in the process of attaching the vertical flaperon control rods to the mixer tube on my Cruzer and the plans call for an AN5 bolt with spacers (C75C2-2) on either side of the bearing. It seems to me that there should be a penny washer larger than the bearing race next to the bolt head that would prevent the separation of the control arm from the bolt, should the bearing ever work its way out of the race???? I think this is fairly standard practice...however in this case a standard penny washer for a 5/16th bolt would prevent the range of motion which I assume is needed....hence the spacers, C75C2-2 which allow for extra range of motion. So....
1. Should a washer be installed here, it would have to be fabricated or modify a 5/16" penny washer w an OD of .625, so not to interfere with the range of motion.
2. What have others done when a bearing is next to a bolt head at this location and others?
Replies to This Discussion
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Permalink Reply by Raymond Paul on
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Hi Don, yes correct you need a penny washer for safety. I have done this on my 701 build. You will find the penny washer wont restrict movement as your spacer C75C2-2 that fits between the rose joint and bracket C75C1-7 acts in the same way as the penny washer.
So in effect the range of movement of the rose joint is actually limited by bracket C75C1-7 in this case.Make sure once you add in the penny washer and the 2 spacers C75C2-2 you still have 2-3 threads of the bolt thru the nut.
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Permalink Reply by David J. Beaulieu on
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What is the purpose of the penny washer in this instance...prevent wear on the inside facing of the bolt head by the spacer or bushing?
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Permalink Reply by Don Morrisey on
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The purpose is to prevent the rotating bearing from disengaging with its mother ship (the bearing body...CW-5-12) and leaving the pilot with no control...which would happen if the bearing component ( the rotating part) of CW-5-12 disengaged, because the OD of the rotating bearing is bigger than the bolt head. If there is no other surface, bigger than the rotating bearing itself, separation is possible. An oversized washer (penny washer) prevents this, because the "penny washer" is a larger OD than the rotating bearing. The rotating bearing may indeed separate, but that oversized washer would prevent the head of the bolt from disengaging with the entire thing....thereby ensuring control, no matter what. I could be wrong, but I think this is required in Canada. I was surprised to see Zenith plans not calling for this oversized washer in general, as I believe it is fairly SOP these days...
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Permalink Reply by Brad Rawls on
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Don -
On my 601, the penny washer was too big, it kept interfering with the heim joint at extreme angles. I ended up using a standard 5/16 grade 8 washer and it fit perfect. My DAR told me I had to have it on each heim.
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Same here...I found those washers at Home Depot yesterday!
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Permalink Reply by John Austin on
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Although this is simple and inexpensive insurance against a potentially serious problem, I've never seen a report of an aircraft accident attributed to a heim joint failure (or for that matter, even a report of joint failure without an accident!). I did a quick Google search of "aircraft heim joint failure" and did not find a single hit in the first several pages I scanned - all references were automotive.
On the other hand, in the automotive racing world, it is apparently a very common type of failiure. However, in racing, the loads are many orders of magnitude higher - such as in a suspension application. Of course, one might suspect a racing car to be rather "abusive" to the joints and the engineers will commonly attribute failure to improperly designed joint geometry and bending loads on the joint.
It would seem that a heim joint failure in an aircraft control system is an exceedingly rare event. But, no matter how rare, if a few cents' worth of washers can prevent an accident due to a rare but potentially catastrophic failure, why not install them!
But, just out of curiosity, has anyone actually seen such a failure?
John
N750A
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Permalink Reply by John Burns on
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Thanks for bringing this up. It is considered best practice in most cases, just in case the ball slips out of the cage. Since you brought it up I will get the washers ordered now instead of waiting for them when I need them in a few weeks. THANKS
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Permalink Reply by Gary Welch on
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The EAA website has a video on this subject for those that are interested.
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Here are the links for the videos. Hints for Homebuilders Jack Dueck
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I bought the current airplane I'm flying (Varga 2180), from Brian Carpenter...part of my insurance requirements were 5 hours with a CFI in Type and Model....Brian is also a CFI, so I got my 5 hours of dual from him....have to say he was the best instructor I ever had, just had a great way of conveying the message. I ended up flying that plane from Corning CA (where he lives) to Massachusetts. Great instructor and all around good guy.
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