Wing skeleton/skin drilling order

How critical is the wing skin to skeleton assembly/drilling order? What I mean is that Van's instructions tell you to assemble the skeleton, match drill all the attach points, disassemble, prime, then rivet the skeleton together. Then you are supposed to attach and match drill the skins to the ribs. I'm not a fan of drilling through and deburring metal that I have already gone through the trouble of priming, it seems to somewhat defeat the purpose. The most at-risk parts (rivet holes which are most likely to get water seeping in them and sitting) are being cleaned of primer. I know I could just re-prime them, but then they won't have the etch or alodine in them as they would if done beforehand. So is it a bad idea to attach the skins to the clecoed skeleton and match drill (and deburr/dimple) prior to priming the ribs and riveting it all together?

Zach--

I wondered the same thing a few weeks ago when I was at that point, but have concluded a couple of points, which may or not be valid:

1. Riveting holds things together more tightly than cleco's. This is especially important if the wing ribs and rear spar are hanging from the main spar on a fixture. Collectively, they are relatively heavy. While a few one hundreths of an inch of play that the clecos MIGHT allow may not seem much, you really want your wing skins to go on and drilled to the FINAL dimension of the skeleton. Straight wings are probably kind of important. : )

2. You will have to check for twist a number of times while fitting your skins, before and during drilling, etc. The clecos may not hold everything firmly together when you are removing the twist and then keep the twist out.

These assumptions may be entirely incorrect. I didn't worry about your concerns, only because my priming regimen is not as exhaustive as yours. I'm one of those "middle-of-the-road" primers. I'm just using DuPont Variprime on everything--not a multistep process.

You might check with Van's on this one. I'd be curious what you find out.

Good luck,
Steve

I was thinking the same thing just the other day. We are getting ready to rivet out vertical stab together. We did what you are suggesting. Clecoed the whole thing together and then drilled, deburred etc. This was pretty easy on the small V/S but I would imagine the wing would be hard to do. Has anyone done this to the wing?

I did my whole emepennage this way, too.. So that's why I was asking. There was only one cut in primed metal on my empennage, and that was the front spar cutout for the elevator horns...

zsadecki said:

How critical is the wing skin to skeleton assembly/drilling order? What I mean is that Van's instructions tell you to assemble the skeleton, match drill all the attach points, disassemble, prime, then rivet the skeleton together. Then you are supposed to attach and match drill the skins to the ribs. I'm not a fan of drilling through and deburring metal that I have already gone through the trouble of priming, it seems to somewhat defeat the purpose. The most at-risk parts (rivet holes which are most likely to get water seeping in them and sitting) are being cleaned of primer. I know I could just re-prime them, but then they won't have the etch or alodine in them as they would if done beforehand. So is it a bad idea to attach the skins to the clecoed skeleton and match drill (and deburr/dimple) prior to priming the ribs and riveting it all together?

Click to expand...

Rivets expand and fill the hole, so there's no room for water to get in and sit. Contact between the rivet and the hole should be metal-to-metal for strength anyway! Also, if you have the correct sized hole, the rivet will scrape away the primer - or you may have to run a drill through the hole to get the rivet to seat properly.
I'm using AFS etch & primer (I'm almost done with my empennage) and I primed my ribs and stiffeners prior to fluting, final drilling, deburring, and dimpling and that primer stayed on just fine (tough stuff!).
Corrosion inside rivet holes is *way* down on my list of worries (and I'm an Aero Engineer

Dennis Glaeser
7A - Empennage

So here is the response from vans:

Well, it seems to make assembly easier for us if we break it into
stages. We do prime parts on our prototypes (even though many
of our builders don't) but we've never used alodine and aren't too
fussy about the priming process.

Our procedure is certainly not the only one that would work. If you
want to do it a different way to suit your needs, by all means, do so.

Click to expand...

I'm not sure that I believe the theory that water can't get into the rivet holes once the rivet is set. If that was the case we wouldn't need to use proseal on the tanks... And there's always some slop room in those rivet holes when you dimple, as it stretches the hole out a bit during dimpling.

I'll probably just drill it after assembly and then give it a quick primer shot afterwards to fill what the drill/deburr took off. But I have to finish my leading edge ribs first, so I have a little time to think and decide.

I use the Alodine pen on holes in pieces that have already been primed.