skin rivet order

[prestwich]

Finally I'm actually ready to start riveting my HS skin. Seem to recall hearing about starting at a certain place and going in a certain order in order to keep the skin tight. But, with all the holes match drilled, if the skin *did* stretch as I go along, wouldn't that mess up the hole alignment? And, doesn't keeping non-riveted holes clecoed keep everything in place anyway?

I'm confused, as usual. What I *want* to do is go around in kind of a random, cylinder-head-bolt-torquing type pattern. What's the story?

[captain_john]

Well, it is kinda like making the bed and smoothing out the sheets.

You don't wanna go in a "bolt sequence" but rather an inside to outside manner. This will force the excess material to the perimiter and mitigate any oil canning.

On the HS, start at the leading edge and then down each forward spar. Then you work down the ribs. Once onto the rear spar, I went from center of each side... inboard and outboard.

Ya know whattImean?

CJ

[prestwich]

Ya know whattImean?

CJ

Yeah, but, yeah, but, yeah, but, IF the skin stretches, isn't it gonna pull those perfectly match drilled holes out of alignment? And wouldn't that be a *bad* thing? And couldn't I *prevent* that from happening by ping-ponging around in my rivet sequence?

Both ideas make sense to me, but they're contradictory. That's why I'm confused!

[Spike]

It can be confusing. I think CJ said it very well with comparing it to wrinkles in the bed sheets. I dont believe that the metal moves enough to really botch up the hole alignment. Im guessing its because the first thing that we do with these holes is drill them to size, then we debur them, and finally we dimple them which stretches out the hole. In the end the tolerance in hole alignment is not nearly as tight as it was when the holes were prepunched from the factory.

Now, lets pretend that there is going to be some runout as we rivet that skin on as it starts sitting really tight up against the skeleton. By riveting from the center out, you are stretching that runout across the entire surface. However, if you start skipping around, you confine that runout to subsections of the skin. If you think of it in the worse case, rivet the opposite ends first, and then work your way inwards. As you do that you will be subsequently forcing that runout into a smaller and smaller area which can produce that oil canning that CJ was talking about.

The idea is to spread that little bit of unperfect fit across as large of an area as possible.

At least thats how I think of it

-- Spike

[captain_john]

Welllllll...

I see what you are saying, but the smoothing thing is the standard method.

Mebbe the skeleton underneath moves in a commensurate fashion? It isn't like a cylinder head that must conform to the piston, cylinder and what not. The skin must conform to the skeleton. If the skin stretches, so must the skeleton and vica-versa.

I dunno... it is just the way it is done.

CJ

[Dan A]

What I found is if you start in the m iddle and work out to the ends, skipping 2 holes at a time, It will come out very good with very little streaching. After you have done the skipping routine, go back and fill in the remaining rivit holes. Works great!
Dan

[captain_john]

Yes Dan, on a large skin the center IS where you wanna start.

On my wing skins I started in the center and worked outward also. Only diff... I didn't do the alternate hole method. I moved a cleco every time. I just felt better about it that way.

...and isn't that what the whole thing is all about? How it feels?

CJ

[Dan A]

Actually, clecos will let the skins move a little whereas rivits won't. That's why I chose to do the skip hole method. And I'm not shure "how it feels" is as good as'How it fly'!
Dan

[svanarts]

Once upon a time someone once told me that you want to make sure the skins are warm before you drill them or rivet them. I guess you prepunchers don't have much of a choice on the drilling. The reason being that the skin will expand when warm and will be expanded to the max. Then once you rivet it together and the skins cool they draw up nice and tight. No oil-canning.

I did one wing in the summer (100+ deg weather) and the other in the fall/winter (60 deg weather.) I don't see much of a difference in either wing. They both look like they were pounded together with a sledgehammer.

[captain_john]

I don't see much of a difference in either wing. They both look like they were pounded together with a sledgehammer.

Were they?

I read in the RV8OR how people are totally wrapped up in the heating process. Wicked Stick is VERY critical about temperatures when he does his skinning. I am not so. His skins look GREAT!!! He does take LOTS of care in the entire process and it shows. As far as does it matter what the temperature is when you do the skinning process... I dunno? Does it hurt? No...

CJ

[prestwich]

So says me:

Spike gets the "clarity of explanation" award here. Dan's approach seems to me that it makes the most sense from a purely logical, rational standpoint, kind of a good compromise of approaches. And, brings up a good point about clecos not holding things in perfect alignment.

The temperature thing is interesting; never heard about that before. I know metal changes size with temperature, but I'm skeptical that it would change enough to notice. Worth reading more about it, though.

I posed the question to Van's tech support:

"I'm ready to skin the HS. If I understand correctly, the common wisdom is to work from center to ends, to avoid "oilcanning" if the skin should stretch a little as you go along. That makes perfect sense to me.

"But - this is where I'm confused - it seems to me that *if* the skin stretches, the holes at the end of the row will no longer be lined up. So it seems that a more random hole riveting order would keep all the matched holes lined up.

"Both of these philosophies make sense to me, but they're obviously contradictory. Can you help with this?"

And, I got this reply:

"It really doesn't matter much -- the sequence is much more about
progressive access with your hand(s). You won't see the skin
"stretch" in metal this thick and pieces this small."

So it's time to buck rivets.

[Spike]

Excellent Post. Goes to show what we do, and many times dont know!
Thanx Vans.

-- John

[poeboy]

When I was riveting my HS, I followed the approach on the Orndorff tapes, starting at the mid-point of the front spar and working outboard and aft. I didn't have many clecos in place and discovered that the skin did flow and stretch sufficiently that I couldn't make the holes line up at all. Had to drill out a bunch of rivets and try again. The second time, I kept as many clecos in as possible, would jump ahead and rivet, say, the 6th rivet away from where I was working, then come back to the intermediate ones in between. The "jump ahead' rivet kept the skin from moving to that point and all was well. The results was a nice tight HS with no detectable warping or oil-canning. YMMV, but, at least in my case, the skin "flowed" quite a bit when trying to rivet in a linear fashion.

-poeboy