7A elevator spar crack

[N526JS]

Checked my buddy's RV-8 today for loose jam nuts. About 300 hrs on the hobbs. 3 out of 4 elevator nuts were loose. None on the rudder. The nuts were not just a little loose, they were way loose as you could just spin them with one finger.

[rvbuilder2002]

Originally Posted by tc1234c

I checked all my jam nuts on tail and all of them are good. This is after 1,370 hrs of service.

I also checked a friend's newly acquired low time RV. I found all the jam nuts on elevator and rudder were loose.

I did not use a torque wrench on mine. But from the outcome I can conclude that they are tight enough. Just offer one data point. Those jam nuts don't always come loose after certain hours in service.

Of course I will continue to check all nuts and screws.

There are a number of different explanations for loose rod end jam nuts.

One obvious one is that they weren't properly tightened in the first place. It is very difficult to use a standard open end wrench, and get them tightened properly.

Another one is paint and/or primer under the nut. Not everyone paints with the rod ends removed, but a lot of anal people do (can't stand the thought of paint on the rod ends and jam nuts). Even if you don't remove the rod ends for painting, most everyone that primed their parts has primer under the nuts (some people a lot more than others).

Paint or primer under fasteners will always have the potential for the torque to drop off over time as the paint/primer gets compressed / extruded from under the nut. It only take a coating a few thousandths thick to have an impact.

This issue can also be present on the rudder and elevator attach hardware but to an even greater extent because the steel attach brackets often get much more primer, paint, and sometimes even a few coats of clear, than would be under the jam nuts. Same problem... different location.

[E. D. Eliot]

Once again, thank you. This is the kind of info that you provide here on the VAF that is priceless. I absolutely no aircraft experience so this kind of tip may even be life saving to me. I may have figured out that I should not paint the rod ends but maybe not. Again, thank you sir!

[rvbuilder2002]

Originally Posted by E. D. Eliot

Once again, thank you. This is the kind of info that you provide here on the VAF that is priceless. I absolutely no aircraft experience so this kind of tip may even be life saving to me. I may have figured out that I should not paint the rod ends but maybe not. Again, thank you sir!

To clarify, an issue painting the rod ends is not what I was describing (though if the are it could soak into the ball/bearing area and cause it to bind up).

The paint / primer issue is primarily if there is a coating between the jam nut and the surface it is supposed to contact (the spar web) when torqued.

[LifeofReiley]

If you have loose jam nuts, you did NOT torque them properly in the first place...

[cajunwings]

Originally Posted by plehrke

When you say they needed tightening do you mean they "could be turned 1-2 flats" or do you mean they "needed 1-2 turns to meet the required torque"?
Just cautioning on turn nuts just because you can and end up over torquing.

I would say they were loose to the point of almost being able to rotate them with your fingers and needed 1-2 flats to not be loose. The rest of the tail attach fasteners needed about 1 flat. No torque wrench used for this operation.


Don B

[Mark Burns]

I got the elevator repair completed and flew this afternoon!
It felt great to get back in the air!!

I just repainted the tip area. I had to replace the fiberglass tip and do all the glass work.
I touched up all the rivets that are in the skin to spar with a small artist brush and you really can't tell it's been apart!



I few quick data points.
My elevators were balanced "together". They were still "perfect" after the spar replacement.

I decided to balance them separately and fly another 900 hours to see if it helps

I had to add 2.4 ounces to the left elevator at the tooling hole. Not sure how much I drilled out of the right counterweight. I had installed a nutplate in the tooling hole during the build so I used it on the left elevator. I also safety wired this bolt just to be sure it doesn't back out.





Mark

[Sam Buchanan]

Originally Posted by Mark Burns

I had to add 2.4 ounces to the left elevator at the tooling hole. Not sure how much I drilled out of the right counterweight. I had installed a nutplate in the tooling hole during the build so I used it on the left elevator. I also safety wired this bolt just to be sure it doesn't back out.

Mark,

Congrats on getting your plane back in the air.

However....that little tab and associated stuff you have added just doesn't give me a warm and fuzzy feeling. If any of that ever managed to get loose it most likely would jam the elevator...and ruin your day. I think this is a case where the cure is worse than the disease.

I would remove the extra weight so I would never have to worry about it coming loose....this arrangement raises red flags for me.

[acroflyrgirl]

Wow Mark looks like you're all ready to head N.
I got in today. See ya soon. Nice work getting all that done.

[131RB]

Mark,
Your fix looks great. Your down time was minimal. Not sure what Sam doesn't like here, it all looks secure to me. Safety is correct and my guess is the bolt securing the weight is either in a nut plate or self locking nut. How much more secure can you be?
Ryan