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Skin buckled against 908-L bracket

coopGT

Member
After attaching the right skin (empennage) and riveting, I noticed the skin was against the 908-L bracket. It is buckled under pressure. Would the correct fix be taking a dremel or like grinder to trim the buckled part so it relieves the pressure? I want to avoid all possibilities of a fatigue crack later on. See attached pictures. Should I ask the mothership?

73 hours in a flawless build and I find this...
 

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Can you take a picture a little further away? Having a hard time picturing exactly where this is in the structure. From what I can see, I would personally file the skin back so its not pressed against the reinforcement bar, but I also don't remember any of my skins having an intereference fit like that. It looks like you may have to take a few rivets out in order to gain access to the edge of the skin. What was your plan for getting a dremel or file in there?

Edit: Also, if I wanted to go look at the drawing for this part, could you confirm you're building an RV9 and the drawing number?
 
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It is a L bracket attached to the spar. I am attaching another picture.
 

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To me it looks like your angle is off on the bracket, it looks good at the top but doesn't follow the angle of the skin. The dimensions on the plans are 1:1 scale, you should be able to set the bracket on the plans and make sure it is the correct angle
 
Please see pictures posted of plans and farther away. The left L bracket has no interference and fit perfect but this one obviously not. It does not have a spar or anything behind it, was hoping to dremel it out slightly away from bracket to relieve pressure and no longer touch bracket.
 
Thanks for the extra pics, make it a lot more clear. I agree with the other people that the bracket looks slightly to large, not the skin. How you fix this issue has two possibilities
1. Make the bracket smaller
2. Make the skin smaller

Ideally you should shave the bracket down a hair and not the skin, but honestly, i think whichever is physically easier would be fine. That section of the tail will be covered by the empannage fairing when fully assembled, so a slight blend out of the skin won't affect the visual look of the final product at all. Either way, I think you have to remove one or both of the parts in order to properly clearance them. You may be able to use a cut-off wheel on a dremel to make a small gap in there and then clean it up with a small file and sandpaper. I personally would take 4-5 of the closest skin rivets along the skin edge out and attempt to pull the skin up and away. You might be able to get away with just removing the closest 2. Don't remove any rivets that are in a closed out area that can't be squeezed/bucked. Only consider removing rivets along the open edge. Then you can file back the edge of the skin until it lays flat again and re-rivet. This allows the use of "oops rivets" if you mis-drill during disassembly. You're also right between the 2 rivets on the skin, so blending the skin has no effect on edge distance requirements or strength if the blend is kept to a minimum. If you drill the 9 rivets on the bracket, you're already at 1/8", so you'd have to go with big *** rivets if you misdrill those holes. I have a few 5/16 rivets in my plane from messing up 1/8 and they're ugly.
 
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There are a lot of posts here about how to remove rivets and some practice on scrap is smart. If you are careful and use great technique you can go back in the 3/32 rivets just like the originals.

If you just drill them out then all sorts of weird results can come to pass. Since the OP didn't ask for rivet removal advice I'll leave that to the other hundreds of posts.
 
I'd be wondering why it happened in the first place...will that bracket be misaligned later on for attaching to something else?
 
Just me

I think i relieved the skin slightly in this area. It is much easier to relieve the skin than the bracket. I would not unrivet bracket, I think it would be harder to get back on straight with good rivets. The skin rivets would probably be more forgiving of rework. JMO
 
First of all, I would NOT drill out that bracket. I agree that based on the picture, it looks like the culprit is that it was made slightly too long, or maybe mislocated slightly to the left, but assuming that's not going cause you and edge distance problem on down the road with whatever the other side of it attaches to (something worth checking now if you can) The easiest way to deal with this is to just relieve the skin and maybe the underlying rib flange if it's interfering as well? (This assumes that you can relieve the stuff other than the bracket without running into an edge distance problem).

What I would do;

1. Drill out a few of those -3 rivets in the edge of the skin so that you can flex the skin up off the underlying structure a bit.
2. Slide a thin stainless steel putty knife under the skin in the problem area to protect the underlying structure.
3. use a ruler, feeler gauge, #40 drill bit etc. to raise the skin edge up off your spar protecting putty knife.
3. Relieve the interference by sanding a nicely radiuses notch in the skin with emory cloth, sandpaper, jewelers file, whatever. Looks like it only needs a few thousandths, so I don't see the need to bust out the dremmel, rotary file, or any other potentially spar destroying power tool that you happen to have.
5. remove putty knife and other stuff.
4. squeeze new skin rivets.

done.
 
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