Elevator Attach Bolts RV-6

[Clarkie]

Maybe you guys can help me out here. I was doing the preflight the other day on the -6 and found something quite startling. As I inspected the elevator to HS attachments, I found one bolt the didn't appear to have much thread showing, less than usual anyway. When I slipped my finger in there, I could easily move the bolt with little to no effort. I grabbed a few wrenches to tightened it up and it tightened with not much effort. Ended up finding two that were "loose", one had what's always been the same amount of thread showing.

My questions are these as I did not build the airplane:

1. How much thread should be showing?

2. After flying the airplane, it occurred to me that how did the bolt back out and why was I able to tighten it? Shouldn't there be cotter keys or some other locking mechanisms on the bolts to prevent this very thing from happening?

Thanks

[rmartingt]

Originally Posted by Clarkie

Maybe you guys can help me out here. I was doing the preflight the other day on the -6 and found something quite startling. As I inspected the elevator to HS attachments, I found one bolt the didn't appear to have much thread showing, less than usual anyway. When I slipped my finger in there, I could easily move the bolt with little to no effort. I grabbed a few wrenches to tightened it up and it tightened with not much effort. Ended up finding two that were "loose", one had what's always been the same amount of thread showing.

My questions are these as I did not build the airplane:

1. How much thread should be showing?

2. After flying the airplane, it occurred to me that how did the bolt back out and why was I able to tighten it? Shouldn't there be cotter keys or some other locking mechanisms on the bolts to prevent this very thing from happening?

Thanks

Plans call for a locknut on these hinge bolts, but no cotter pin. If these nuts had backed off, I would replace them; obviously the locking feature has been compromised. It'll only cost a couple bucks.

[ccsmith51]

On my -4 all those bolts (elevators, ailerons, rudder, etc.) have metal lock nuts, always tight. Maybe something to consider..

[BobTurner]

BTW, you do not just "tighten them up". Use a torque wrench. Without one the tendency is to overtighten, depriving the fastener of some of its strength.

[Clarkie]

How do you get a torque wrench in that small slot? I barely had enough room to get two small wrenches in there.

[sf3543]

FYI
A castle nut and cotter pin should be used any time the bolt will move or rotate in assembly. If the bolt can be torqued down against a bearing surface and the bolt does not rotate, as it is in your example, a fiber or metal lock nut should be used.
Good luck.

[rvbuilder2002]

It would be my guess that the bolts were never fully torqued when it was originally assembled. It is highly unlikely for a properly torqued fastener installed in joints like this to loosen.

I do not use a torque wrench on a difficult to access bolt like these, but I have a pretty good finger feel for what the correct torque value is.
Proper value is 20 - 25 inch pounds. This is much lower than most untrained people would guess. As already mentioned, the danger of you tightening them, if you don't have a good feel for the proper torque, is that you over did it and damaged the bolt (which can be undetectable visually). The yield point of an AN3 bolt is ~60 inch pounds. Almost 3 times the normal torque, but still not very high.

The thread exposure rule of thumb for AN365 nuts (the ones called out in the plans) is at least 1 thread, but no more than 3 threads visible. This rule of thumb does not work with all nuts, so you would need to determine which ones are installed.

[BobTurner]

To torque, use your wrench as a "crow's foot"; put a nut-bolt combination in the free end, and your torque wrench on that. You will need to calculate the torque wrench setting to get 25"-lbs at the nut.

[Larco]

It is probably best not to panic. RVBuilder is most likely correct, as his usually is :-). Some one just got side tracked and did not tighten them. It happens!!!! Larry

[Clarkie]

Thank you all. I think we'll change the bolts and nuts just to be safe.