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Bottom wing skin to fuselage overlap mismatch

sbalmos

Well Known Member
Don't ask me how this happened. I have no idea. When I first fit the wings and drilled the screw holes into the left side fuselage bottom skin "flap", everything aligned. It even aligned while I was final-fitting the wings with the good bolts. At some point, somehow, the wing skin looks like it's angled outboard, getting worse starting at the the 4th screw hole forward from the aft spar, as you head forward to the main spar.

I'm trying to decide whether to leave it alone without screws. Or should I try and have someone push down on the wing tip to see if that would bring it back to alignment?

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Scott, That fit is a bummer. I would call Vans about it. Steve
 
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Scott,
Did it line up at one time when you drilled those holes? I believe the holes came pre-punched in the belly skin, but not in the wing, right? Maybe you don't have the wing all the way home. If everything lines up with the wings and you still have the mismatch, you can fix it. I had to do that on my RV6 many years ago. I'll be at my hangar this weekend (and all week) and can explain how I fixed mine. I have a couple strap duplicators you can borrow.
 
Just got off the phone with Gus. He's not worried about it. Elongating the holes to get a screw in is fine. And no one's going to see the underside anyway.

Scott, I'll be out later this afternoon, once I finish some work and my head stops pounding from these 30 degree swings. :D
 
I thought I read somewhere this joint is somewhat structural, not cosmetic ?
 
If it is, Gus didn't think so. Maybe a modicum of structural strength. He mentioned seeing quite a number of older RVs in the wild where the builder either forgot, missed in the plans, or just didn't bother to drill and screw those screw holes.
 
Good. I wouldn't think it's structural. Hersha will know how to do it.
 
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Just got off the phone with Gus. He's not worried about it. Elongating the holes to get a screw in is fine. And no one's going to see the underside anyway.

Scott, I'll be out later this afternoon, once I finish some work and my head stops pounding from these 30 degree swings. :D

Some Tinnerman washers on those screws will cover up any visible defects in the re-dimpled skin nicely.
 
I've had a 6 & a 7 come thru the shop some years back with those screws not installed at all. I called Vans & was advised they were structural. Was instructed to install them. They both ended up with AN515 (ugly) screws on their bellys, with nylocks in the 7 wing well & a long aluminum strip with nutplates used in the 6 because of very limited access in it's wing well.
Suggest OP call Vans for advise.
 
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Well Gus /is/ with Vans. And he didn't seem concerned (used the classic "none have fallen out of the sky" line on the phone). He was the one who suggested elongating and redimpling the holes. And that's what I did today.

It's done, moving on. Looks tolerable, if anyone ever looks underneath. I like the Tinnerman washer idea. Maybe this weekend.
 
Perhaps the way to look at it is that those fairings are certainly aerodynamic if not truly structural. I've heard a story from a reliable source that flying the plane without them installed makes the plane almost uncontrollable. Don't ask me why this happened...wasn't me. My aft-most hole on the bottom didn't match well and I had to elongate the hole in the fairing and use stainless tinnerman washers to finish the job. Stainless and aluminum will corrode, so prime the inner surface of the washers.
 
Not an engineer nor did I stay at a Holiday Inn Express last night.....but, I can see this adding to + G strength with the bottom skin all connected in tension :rolleyes:
 
screws

Yep I went to search and found lots of info on this subject as I had a ? a few years ago on this same subject.The RV3,4,6 were load tested with out screws in place and 7,8,9 with screws in place so yes they are part of the wing!
Bob
 
Not an engineer nor did I stay at a Holiday Inn Express last night.....but, I can see this adding to + G strength with the bottom skin all connected in tension :rolleyes:

Yep I went to search and found lots of info on this subject as I had a ? a few years ago on this same subject.The RV3,4,6 were load tested with out screws in place and 7,8,9 with screws in place so yes they are part of the wing!
Bob

Odd that Gus would say not structural. Vans will compromise on cosmetics, but not safety. Maybe he assumed that they would still share the loads even if elongated, at least in this direction. He has a lot of experience and surely this discussion has been thrashed with engineering.

Anyway - although they carry some load, the pitch/spacing is not adequate for full skin load transfer, so Scott could just add screws between existing ones and move on. This addresses the strength and offset issue. OTOH - this shifts loads to the skin, and changes the load balance of the structure. Jon Jay said his screws loosened periodically for a while then stopped. So, clearly they do carry see some load, but how much they carry is open for analysis. Back to Vans.
 
. Jon Jay said his screws loosened periodically for a while then stopped. So, clearly they do carry see some load, but how much they carry is open for analysis. Back to Vans.

Another CI or two since that report and they are still tight. There could have been other factors at play. However, the rear spar bolt discussions and confirmation from Scott McD, that joint can move. If it can move, that belly skin must be taking some load at some point. I would suspect it isn't going to be cause or a factor in a wing failure. As you point out, there are too few screws to put that sheet to much work.
 
I thought they are strutural

A couple of years back I also had an RV7 in my shop without those screws. Asked Vans and the reply was: Do not attempt to fly that aeroplane as it is structural. Cannot remember who it was but I find it interesting how opinions differ :confused:
 
Screw alignment issue

Did you go back and check the angle of incidence on the wing as well as check the wing for forward and aft sweep after you ran into this problem? That is where I would start. Wing twist shouldn't be an issue with this particular problem.
 
wondering about this too

I know this is an older post, but I'm now doing my fairings and I just match drilled those holes between the fuselage skin and wing.

My issue/question is about the fit of the overlapping skins. my fuselage skin hangs about 1/8" lower than the wing bottom, and clecoing the skins together of course causes major rippling because of the curved surface. I'm thinking about adding a filler strip between the skins just to make a clean joint, but if it is indeed structural - that would not be the best solution.

Also, if it is structural - the whole method of drilling those holes is very poor: You pre-mark lines along the wing skin and then you are supposed to take a stab at finding those holes in the wing by measuring off of those lines and back 3". Far from a good match drill. I had just enough room to squeeze in a hole duplicator, and made good matching holes, but the geometry of the two skins makes pretty bad ripples. Kind of a tradeoff between structure and aerodynamics for me anyway.

I sent my question in to Van's this am, I'll update when I get their comments.

picture of my wing/fuselage joint.

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