Skin "Stretcher"?

I remember in Jr. High, one of my friends cut a piece of his project too short. The shop instructor said "go get the board stretcher". So... I need a Skin stretcer for my tank skins

Here's my issue. I've assembled the wing skeleton, per the plans. I've also assembled the Leading Edge and Tank assemblies (Clecoed only at this point). So I put the wing skins on the skeleton, everything lined up just fine. I then put the leading edge on, everything was fine there as well. Lastly, I put the Tank on (still cleco'ed only at this point). I put cleco's throug the tank skins into the main spar and, you guessed it... there was a problem (see photo).

Where the top wing skin and the tank skin meet on the main spar, I have 1/16" gap. The holes line up perfectly though. Is this a normal occurrance? I also have a small gap where the LE and Tank skins meet on the splice strip that joins them. .

I'm not quite sure where to go from here... neither one appear to be anything more than a cosmetic issue. If this is "normal" then I'll press on, if not, I'd like to fix them before I rivet anything else on that wing. I went as far as taking measurments looking for twist in the wing, but it came up with only 1/32 difference between the inboard and outboard readings.

Thanks for your help,

Darrin "Dex"heimer
RV-9A - Wings (for 3 years :-( )

I had to remove the skin-to-baffle clecos from the first foot or two on the inboard side because they interfered with the spar- they prevented the tank from settling down fully. That may not be your problem if the screw holes line up though.

I noticed my right tank had a bigger gap than the left- but it was only about 1/32". I have read here somewhere that the gap will shrink a little after riveting.

Don't worry about the small 1/16 inch gap. It will be a bit smaller when you rivet the thing together and bolt it to the spar. Even if there is a gap by time you paint it it will be not to noticeable. Move on.

Make sure the spar is perfectly flat as in not bowed.

Make sure all the rib flanges are at 90?, pay particular attention to the tips of the ribs and the flanges that meet the baffle. The tips tend to have bumps on them around the notches.

Make sure the tank brackets do not have burrs on them creating a gap between the bracket and the baffle/spar.

Put the bolts in thru the spar to the brackets to ensure that the brackets are pulled all the way against the spar.

I would make sure that I had that gap minimized before drilling the splice strip.

A little gap seems to be normal and in most cases a desirable thing because it provides a clean seam for the paint. The skins will also walk up a bit once they are riveted.

Hope this helps.

I've been working through the same thing on my second wing. The first wing
-when I didn't have a clue what I was doing- had no gaps. Now I have a gap on the top between the tank and skins. The tank/leading edge was straight, but the tank skin not seating well at the tip.

After measuring all the z-bracket heights. and following the line of thought in the previous post, I massaged the tip of the tank skin with a small hammer and length of 2X4. This evened out the splice strip and the fit there is now very good.

There is still a strong 1/32 gap, especially inboard between the tank skin/wing skin. I/ve taken the inboard ribs out a couple times trying for the best possible fit. Snugged in the 3 inboard ribs with a ratcheting tie down. Checked the flush rivets under the inboard z-bracket to make sure the are flush. The gap persists. If you try to use a ratcheting tie down around the wing to pull the tank in, the baffle starts to bow. Could be a problem when the proseal goes on.

So, whats left? Filing the z-brackets? Don't want to weaken them. Tried compressing a throw-away z-bracket on one end in the vice, but it failed, bending at the groove in the web.

I think I'll live with the 1/32 gap.

Jerald
Tucson RV-8A

jaypee said:

I think I'll live with the 1/32 gap.

Jerald
Tucson RV-8A

Click to expand...

You want a little gap there. Paint will fill that and you will never see it.

Found it!

Andrew was dead on... don't know why I didn't see it earlier. And the really sad part is that I read the reply and interpreted it wrong. The clecos from the skin to THE BAFFLE interfere, but only on the top side of the wing where the spar is thicker (which is exactly what Andrew said in the first place). I was able to get the tank skin to spar screw holes to ling up, thinking they should be tight, once I removed the offending clecos everything fit like a glove, I have a very small, and very even gap all the way around (1/64th... but I haven't filed the edges yet)

Oh... to completely embarrass myself, I had all of the interior ribs backwards as well I doubt that contributed to this issue but I'm glad this came up or I'd have had flanges on the wrong side of the interior. How embarrassing would that be?

Thanks for all the replies!

Darrin "Dex"heimer