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alpinelakespilot2000

Well Known Member
Has anyone had any issues with an oil canning wing skin that persisted after everything was riveted together?

I have finished match drilling my TOP skins to my left wing. Every panel (skin between rows of clecos) is drum tight, except for the forward-outboard-most panel which "gives" a little if I push in on it. Pushing it doesn't cause any other panel to flex out and it does not remain once the pressure is released. For reference, the J-stringer is already clecoed in.

I'm not too concerned, because since it is in the most-outboard location, I may be able to pull it a little tighter before riveting, if necessary, but wonder if this is something to worry about and, if so, how I fix it.

Thanks,

Steve
 
Steve,

Just follow the directions and start riveting from the center, working outwards. On my first wing I riveted the ribs that were on either side of the center first and then riveted across the spars. I now have an oil canning issue in that bay. On the second wing I started riveting outward on the spar first and then did the ribs followed by spar then ribs etc. Working my way outboard and inboard. That wing worked out great. Still not sure what I'm going to do about the first wing. May put stiffiner mid way up between spar and J stiffiner already in place.

Good luck
 
BillC said:
Steve,

Just follow the directions and start riveting from the center, working outwards. On my first wing I riveted the ribs that were on either side of the center first and then riveted across the spars. I now have an oil canning issue in that bay. On the second wing I started riveting outward on the spar first and then did the ribs followed by spar then ribs etc. Working my way outboard and inboard. That wing worked out great. Still not sure what I'm going to do about the first wing. May put stiffiner mid way up between spar and J stiffiner already in place.

Good luck
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Thanks Bill--
Out of curiousity, when you riveted spar-rib-spar, etc.... did you rivet the entire rib or only down to the stringer before moving farther in or out to adjacent ribs?

I know I'm probably splitting hairs here, but should we be trying to rivet in a sort of inverted triangle pattern, or should we simply start at the center rib and rivet it in it's entirety before moving on to the next rib (and riveting the top/bottom spars in between before getting to that next rib)? (If you can understand what I just wrote I'd be amazed! :D ) Van's instructions in this regard are pretty vague and could be interpreted a couple different ways. In my inverted triangle pattern, the rear spar would end up being the absolute last thing to rivet. Does that sound right, or should the rear spar be riveted in tanden with the ribs as I move out from the center?

Regarding the stiffener if the loose skin remains... if that would fix the problem, why not? Fortunately for me, since my looseness (if it still exists after riveting) exists at the most outboard panel, I'll be able to decide later if it will require a stiffener.

Thanks again for the help.

Steve
 
alpinelakespilot2000 said:
Thanks Bill--

Regarding the stiffener if the loose skin remains... if that would fix the problem, why not? Fortunately for me, since my looseness (if it still exists after riveting) exists at the most outboard panel, I'll be able to decide later if it will require a stiffener.
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Steve, have you already riveted leading edge on? Because that outer rib, if memory serves, isn't riveted but remains clecoed until the leading edge is installed which could be the source of some wiggle.

You know, I still can't explain why but Van's had a specific order to cleco the skins on in the first place and they were right. I found the fit was much better if it was clecoed to the main spar first and then clecoed along the ribs toward the rear spar. I can't explain why but it just fit better and the holes lined up better than those occasions when I'd just put it on and cleco here and there.

So I was careful to rivet in that order, following the Orndorff method was start with the main spar and go down the rib and out in both directions.

But, again, the other thing you have to remember is you haven't riveted on the bottom skins yet. Those skins -- when installed -- are going to keep the outboard rib from flexing. In other words, it's going to keep that oil canning last panel from, well. oil canning.

It will. Trust me.
 
Thanks for the encouragement, Bob. I haven't riveted ANYTHING yet except for the main ribs to the spars (and yes, that outboard rib is still only clecoed to the main spar). I'm not too worried about it now, but do agree that clecoing in Van's order does seem to work fairly well. Riveting in that order as well seems to be the thing to do, so I'll approach it that way and see how tight everything is after both top and bottom skins (and leading edges) are riveted together. I am probably worrying about nothing, but thanks again. I'll try to remember to post the results of my efforts when I get to this stage in a few weeks. (Oops--still got fuel tanks to go--better make that in a few "months"! : ) )

Steve
 
alpinelakespilot2000 said:
Thanks Bill--
Out of curiousity, when you riveted spar-rib-spar, etc.... did you rivet the entire rib or only down to the stringer before moving farther in or out to adjacent ribs?

First, I had already riveted the leading edge on and had the tanks in place with every third screw installed. When riveting the ribs I would start at the "j" stiffiner position and rivet out from there in both directions. Several rivets towards leading edge and then several towards trailing edge until entire ribe was completed. Then move on across both leading and trailing spars, etc. If you install leading edge first you can use squeezer but if you wait you'll have to buck them also. Leading edge also helps keep everything straight with minimal sag which helps with main skin installation. I think with the other comments you'll be fine. One other thing, I went to the local auto supply store and picked up a creeper which enabled me to rivet the aft half of the wing without assistance (wing still in jig trailing edge about 18" off floor).

Enjoy?
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Back in the old days (???) when I was building my RV6 (Mid 90s) there was a lot of talk about this and how to get tight wing skins that didn't sag in the sunshine when you parked the plane outside.
One answer was to heat up the wing skins while keeping the wing ribs cool, while you were riveting. The idea was that the skin expanded from the heat, while you were riveting and then when it cooled/shrank back the skins would be nice and tight.
Now, I don't know how valid this is, but the method was to shine some high wattage lights on the skin from the outer side and keep the ribs shaded so they didn't get as warm as the skin.
I actually used this method on my wing top skins. (Didn't do it when I riveted on the bottom skins) and over 900 hours of flight and 8 years I never noticed any sagging or oilcanning on the wing skins.
It's possible that the lights had no effect what so ever on how things turned out, but thought I'd pass it along anyway since it was kind of a big deal way back when.
 
There's an article in 2X Years of the RVAtor about this and the need to keep the heat even, else you end up with something substantially worse than the problem you're trying to prevent.
 
Oil canning

Steve,
Although I don't know for sure, I don't think you'll ever get all of the oil canning out. I have a 7QB that I've been flying for 230hrs. Under certain lighting conditions in flight I can see oil canning in the outerbays of the wings when I move the ailerons. I assume this is because moving the ailerons puts some parts under load. Also, with the new -7 rudder, which has extremely thin skins, if you are flying form off of me, you'll see my rudder oil canning, even in straight and level flight.

Tobin
 
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