Wing skin boo boo

[nichzimmerman]

Any kit or scratch builder is susceptible to making the mistake I just made, so a public confession wouldn't hurt.

While riveting a wing skin to the nose ribs (poor access to the shop head) I apparently slipped the bucking bar off the rivet and caused a little dent in the skin. I removed the few rivets we already drove and used the Dremmel to remove the scratch on the skin, then realized I had slightly sheared the skin.

Lesson 1: always carefully inspect a ding in the wing skin

Now I'm ready for lesson 2, how do I fix this? My initial idea is to turn the area with a crack into a small hole. As long as I keep it away from the rivet hole, there should be no structural issue since we drill holes in the leading edge skins for other things like pitot tubes. Then I create a back plate and filler for the hole, but those will be cosmetic additions only. Make sense?

IMG_20190807_061743661.jpg

IMG_20190807_061834116.jpg-Nic
Scratch building 4 place #1217

[geraldmorrissey]

Check FAA AC43.13-1b.
Gerry
Patrol #30

[nichzimmerman]

That is sage advice, but 43.13 only addresses structural repairs as far as I can see. My premise here is that I can remove the damage by drilling a 3/8" hole and call it structurally sound. These skins are obviously structural, but we drill un-reinforced holes in them for fuel drains, vents, grease nipples, pitot tube exits in leading edge, etc. So why can't I drill a small hole here and plug via non-structural means? I'm resisting structural reinforcement because that would involve sandwiching a patch between the skin and rib, or have an ungly external patch.

[alaskabearhawk]

I would ask Bob.

[Gr8apmech]

if the 3/8 drill will remove the cracked skin, then that would suffice - you could also plug the hole after drilling. difficult in thin skins but flush plug the hole for aesthetics could be done.

[way_up_north]

I usually remake parts...cause this would trigger my ocd...lol

How about putting it back in place to shape
Drill the ends of the crack.... then put a bead of weld over it... dremel sand it back to shape

Pass anything I type past bob .....

[jaredyates]

No welding allowed on 2024-t3 since it is heat treated.

[geraldmorrissey]

If it's going to keep you up at night, replace the skin. If you think your eye will be drawn to it throughout your ownership of the plane, replace the skin and hang it on the wall. Aluminum is cheap. It's a learning experience. But it's your plane, you'll make the right decision.
Good luck
Gerry
Patrol #30

[Bcone1381]

You wrote:

These skins are obviously structural, but we drill un-reinforced holes in them for fuel drains, vents, grease nipples, pitot tube exits in leading edge, etc.​​​​​​ ​So why can't I drill a small hole here and plug via non-structural means? I'm resisting structural reinforcement because that would involve sandwiching a patch between the skin and rib, or have an ungly external patch.

My thoughts....I think we cant drill holes for fuel drains, pitot tubes and grease nipples too close to an edge, whether that is the edge of a skin, a lightening hole, or a rivet hole with a rivet in it. I think minimum rivet spacing requirements are one guideline that you'll want to honored. That skin is going to feel some stress in flight where the rivet attaches the skin to the rib. The small crack will likely grow, so a small patch designed to carry the load seems prudent if the spacing between the rivet hole and the damage is too close.

AC43.14 says spacing between countersunk rivets shall not be less than 4D. If the damage is small enough and spaced far enough from the existing rivet hole then I could see drilling out the damage and installing a rivet. If spacing is too close, then It seems to me that a patch (IAW AC43.13) is called for that will involve dealing with the associated rib.

I wonder if instead of a sandwiched patch between the rib and the skin, if the patch cold have a 90 degree bend in it at the rib, or be fabricated with a joggle and bend to go on top of the rib flange. Patching it sounds like a great deal less work than skin replacement and could be made invisible with some filler and paint.

But those are my thoughts......What did Bob say?

[BravoGolf]

The second photo has very light lines that appear to be marks from the edges of the rib flange. Is the crack at the “open” side of the rib or up against the flange bend? If it’s on the open side you could create a patch with a joggle to fit over the rib flange, there is guidance in 43-13 for this but it’s kind if buried and not well written. There is a topic for patching a hole, which is what you will need to do to fix this crack.

EDIT Look at page 4-26 paragraph f and then reference figure 4-16 on page 4-32. The skin is structural so you will need a structural repair.

I believe you will spend more time creating a fix for this than you will replacing the skin. And you may not be happy with the look of a fix once it is done.

[N3UW]

I agree with the advise of talking to Bob. I would also agree with Brooks that a simple patch would be acceptable. It seems like a lot of unnecessary work to replace the entire skin for this. We deal with simple wing skin cracks like this with diamond patches on the surface. I would probably consider a flush patch with a doubler under the patch following ac43.13 as guidance.

[nichzimmerman]

Thanks for the input all. Given the variety of opinions, I'll definitely ask Bob and provide his answer here.

[nichzimmerman]

Bob says drill a 3/8" hole and call it a day.