Flap rod end security

Going over my recently purchased RV6A with an AP (Aus equivalent of a DAR) we were both mildly concerned about the lower rod end bearing on the flap linkage. While the upper rod end bearing is nicely secured the lower end uses a bearing with an integral 1/4" stud, ie no place for a safety washer.

After consulting the preview plans I found that a CM-4S bearing with integral stud is indeed the correct fitment at this location. But it just doesn't look adequate for such a high stress component.

Is there another way of securing the lower end of the flap linkage, or am I unduly concerned? Appreciate your thoughts.

Mal

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It is correct as per Vans, and it also contradicts "best practice" - as you've found.

I am not sure anyone has found a better / more correct way of doing it? Nor if anyone has suffered a failure?

It can also take a "home made" spanner to tighten the nut inside the flap (likely depends on type and how it is finished).

All I would suggest is ensure you leave the flaps partially down at shut down, and check the security of that fitting on every walkround.

Thread locker

IIRC instructions also call for red thread locker during install.

Malndi said:

Going over my recently purchased RV6A with an AP (Aus equivalent of a DAR) we were both mildly concerned about the lower rod end bearing on the flap linkage. While the upper rod end bearing is nicely secured the lower end uses a bearing with an integral 1/4" stud, ie no place for a safety washer.

After consulting the preview plans I found that a CM-4S bearing with integral stud is indeed the correct fitment at this location. But it just doesn't look adequate for such a high stress component.

Is there another way of securing the lower end of the flap linkage, or am I unduly concerned? Appreciate your thoughts.

Mal

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Simple fix, use a drill bit to remove the stud, and replace with a bolt and large washer.

Standard proceedure in Canada

Peter

I replaced the CM-4MS rod end with a CM-4M rod end, an AN4-15A bolt, spacer washers and 5/8" OD safety washer. The spacer washers & bolt length gave a much better alignment of the flap pushrod thru the fuselage opening. Also replaced the aluminum pushrod tube with 4130. Overkill - maybe? Peace of mind - yes. Picked this up on VAF - what a resource!

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Another way to look at it......

This is the most easily inspected control system connection (rod end) on the entire airplane.
With the flaps extended (the way most in the know owners leave them positioned on the ground, so that someone doesn't unknowingly step on them when climbing in) it is right in plain sight and should be part of any pre-flight inspection (everybody does those right?).
The likelyhood of a failure occurring on that rod end during a flight (at least a failure that would be prevented by having a safety washer installed), without there having been some evidence of an impending failure that could be caught during a preflight inspection, is just about zero.

BTW, the photo in the previous post concerns me a bit.
The amount of washers visible makes it look like (could be wrong) that the stud length is quite a bit linger than if the specified rod end with integral stud is used. This would be causing the bending load on that stud (bolt) to be much higher than it is with the specified part.

110% Scott..... I don't just look, I put my hand on these and give them a wiggle every flight.
2500 plus 6's flying, largest in the fleet, and I have never heard of a failure of the bearing.....

Preflight

Same here: I check those on every preflight since they are so easy accessible, and that's good enough for me.

No problems so far on none of my -7's (315 hrs / 60 hrs)

Thank you all for your advice. I am persuaded to leave things alone, particularly by Scott's explanation of the unlikelihood of inflight failure. I already park with flaps down and this item is on my pre-flight checklist, but I now have a better understanding of what I'm checking. Thanks again.
Mal

Stock Vans stud-type bearings with Loctite Red for the nut has been working perfectly fine on my RV-6 since it was built in 2003. No worries there. All the load on it is in shear anyway, and very little vibration to affect it. The extruded hex aluminum flap pushrods from Avery were treated with Loctite Blue in case they ever need adjusted or removed.

Flap Rod Ends

I was asked to clarify this on a reference I made to it on another thread, so here it is with a picture to start.

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I installed this per a picture I posted previously on this thread, then changed it back to the Vans CM-4MS bearing because of Scott's concern re bending moment on the bolt, then changed it back to the picture above (right side) as required by my MDRA inspector on final inspection. He indicated he saw the CM-4MS type bearing fail in other applications.

Note:I tried to minimize the bending moment on the bolt by keeping the washer stack next to the rod end as low as possible - the picture shows 4 washers - I was able to come close to the geometry of the CM-4MS with 3 washers. I think I may have had up to 6 washers on the initial installation.

I'm not promoting either way. This is just what I had to do.

Champ said:

He indicated he saw the CM-4MS type bearing fail in other applications.

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If there is any accident reports or other data that he could provide info for, I would sure like to see them.

Sorry Scott. I guess I should have been more clear. The failures he was referring to where industrial and that apparently influenced his opinion right or wrong. Vans design is proven by experience on aircraft, I hope what I was asked to do performs as well.

Champ said:

Sorry Scott. I guess I should have been more clear. The failures he was referring to where industrial and that apparently influenced his opinion right or wrong. Vans design is proven by experience on aircraft, I hope what I was asked to do performs as well.

Click to expand...

Or, now that the inspection is over, you just decide to do what you think or the designer thinks is best, regardless of the inspector's (seemingly suspect) opinion.