Elevator skin crack question...

[TravisHamblen]

This afternoon I made a very disturbing discovery during a pre-flight inspection of my RV-7A. I noticed a skin-crack around a rivet on the top of the right elevator. The crack goes around (making a ?V? shape) the forward most rivet that holds the stiffener on under the skin. The crack was about ? and inch in length on each side of the rivet. I took some photos to record the crack and my (temporary) solution.

To correct the problem (until I can reskin the right elevator), I stop drilled the crack at both ends, and deburred the drilled holes. I then taped off the area I wanted to patch and made an exterior skin patch using JB Weld. I made sure the JB Weld went into the crack and also made about a 1.25? square patch covering the surface of the entire effected area. I was careful to stop the patch close to the drilled holes so that I could closely monitor for continued cracking. Once it all cures for a couple days I plan to fly the plane to see if the patch holds or if the cracking continues beyond the stop drill holes.

I know of a couple people that this has happened to, but never to me! I know it is not uncommon, but it sure is upsetting to find! I wanted to get a consensus on what others have done in the past and if they were successful. I do plan to reskin the elevator just so it is perfect, but hope that the patch and stop drilling will work to keep the plane in service until I get done with the new skin. I would love to hear anybody/everybody's opinion on this and let me know if my temporary patch is/was a good idea.

Take a look at the below linked pictures (view them from the bottom up).

http://www.flickr.com/photos/26323343@N05/?donelayout=1

 

[DanH]

Travis,
I kinda doubt a layer of unreinforced JB weld will do any good. Since you plan to re-skin the elevator anyway, you might consider a riveted sheet aluminum patch using blind rivets.

 

[Phil]

Wow. I was expecting a crack that radiated from the rivet hole. Not around it.

That's bizarre. Any ideas what the source could have been?

 

[TravisHamblen]

Wow. I was expecting a crack that radiated from the rivet hole. Not around it.

That's bizarre. Any ideas what the source could have been?

I GUARANTEE it has to do with the stiffener directly underneath it. I would guess that the crack follows the radius of the underlying leading edge of the stiffener.

 

[TravisHamblen]

Travis,
I kinda doubt a layer of unreinforced JB weld will do any good. Since you plan to re-skin the elevator anyway, you might consider a riveted sheet aluminum patch using blind rivets.

Theplan is that if this holds until I get it reskinned then that is great, it cost me nothing. If not, then I will re-stop drill the crack one more time and install an aluminum patch that would hold together the space shuttle. Just buying flying time until I can get the new skin on. But thanks a million for your input!

 

[gasman]

Maybe a temp patch..... .016 cut in a circle, drill a hole in the center to find the rivet head later to drill out. Then stop drill with 1/16" and then glue ?? with what you think might hold.

 

[mannanj]

Stiffener

You're right about the stiffener. Just guessing, the forward edge roll you put into the skins where they fit behind the horizontal stab was slightly underbent, and you had to put considerable force on them to make them fit together to pop rivet them into place.

Further guessing, that tension made the elevator spar leading edge the fulcrum point and that there was significant uplifting of the skin at the point where the stiffener leading edge begins which caused the crack.

Hopefully I explained my idea well enough. I may be wrong, but it makes sense to my pea sized brain right now.

 

[AlexPeterson]

Travis, I had three similar cracks on the rudder of my 6A at around 200 hours. Drilled 'em and haven't looked back. Almost 800 more hours and no further problems.

 

[rvbuilder2002]

Not caused by what you might think...

This is caused by the leading edge skins not being rolled quite enough before they were riveted together. This causes a slight levering of the skin a crossed the spar when they are pulled together and riveted. Add a little drumming movement of the skin with an accumulation of flight hours and it cracks. The levered load is concentrated at the fastener closest to where the levering is taking place (spar).

Your JB weld will likely not help at all, but it wont hurt anything either (other than make it even more noticeable).