M

Michael Brown

Active Member
Today we got the top skins on both wings, everything looks great. Except the right wing. I have some oil canning at the lap joint. The wing is straight and I am really unhappy with this.

What are my options for correcting this?

Is there any benefit of drilling out the rivets on the lap joint and riveting again? Or heating the garage up to maybe 90 F and riveting again?

Thanks
 
Drilling??

No advice from VAF....

This week I will be drilling out the lap joint and trying again. I will post how it turns out.
 
Old RVator ideas

In some of the older RVators, maybe mid 90s, there were several articles on using heat in order to get very tight wing skins. It involved keeping the skin heat expanded but not allowing the wing structure/ribs to be heated.
It included using halogen lights as the heat source, on the outside surface of the skin, while riveting.
I don't remember all of the details, but you could research it.
 
I still say that heating the skins can't make any difference given the tiny amounts of dimensional change over the length of the sheet.

Last time I guesstimated this, I came up with 50 thousands difference for 20 degrees C of change over a 3m section of skin. You can't tell me that 5/100" over 10' of wing will (as everyone claims) make them "drum tight".

The flex in the underlying skeleton would far overwhelm that amount of difference (not to mention that if it *did* work and made them super-tight, it would put all of your rivets in a shear condition, would it not?).
 
You would be quite surprised at how much of a difference a little heat can make. Go out to your wing and heat up the skin between two ribs by 40 degrees, you will get instant, significant, oil-canning. The oil-canning will go away when the temperature returns to normal.
 
Three of us were building RV-6 wings in the winter of 1990. Two of us heated the skins while riveting. The third person did not. The two airplanes with heated wing skins are "drum tight". The other one was so loose that he had to add stiffeners between the ribs.
I promise you it can make a significant difference!.
 
I'm certainly no expert, and although an engineer, not an ME, and this is my first plane (second, kind of), but I'm just unconvinced...I'd ascribe significant differences in construction as described more to technique than something related to temperature, especially for such small (relative) differences as we're talking about here (10-20 degrees centigrade, probably, max?).

Wing skins are 2024-T3.

CTE, linear 68°F 23.2 µm/m-°C 12.9 µin/in-°F AA; Typical; Average over 68-212°F range. (ASM Material Data sheet, http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA2024t3)

Wings are comprised of 4 skins top and bottom, so let's take the biggest one and say it's about 2 m long (not in my shop at the moment). Heat it up to, say, 120 F, which I think would be the most you could do and handle the material. Keep it that way while you're riveting it. Assume 68 F for ambient.

120-68=52F, or 11 C.

0.0000232 m/m/deg * 2m * 29 deg = 0.0013456 m = 0.05 inches.

I can *flex each rib* way more than 5 hundredths of an inch during drilling, dimpling, or riveting! :)

(ETA to fix incorrect degrees...used wrong conversion earlier)

I don't buy it...sorry...
 
Last edited:
WingsOnWheels said:
You would be quite surprised at how much of a difference a little heat can make. Go out to your wing and heat up the skin between two ribs by 40 degrees, you will get instant, significant, oil-canning. The oil-canning will go away when the temperature returns to normal.
Click to expand...

Same computations, but use .3 m and 22 C

0.0000232 * .3 * 22 = 0.00015 m = 0.006"

6/1000" of an inch is making significant oilcanning?

Hey, I could be all wrong on this, and next time I have my wings down, I'll run an experiment and see what happens. But for now, I still believe that the skeleton flexing during construction, or inaccurate drilling, or some twist creeping in during riveting will cause WAY more than any change in temperature for these small pieces of metal and max temp change.
 
Mel said:
No Problem!
I just know that I've built more than a few airplanes, and it works for me.
Click to expand...

And I'll bet that in doing so, your construction techniques are very good...

I'm not trying to argue or be pedantic, and lots of people here know way more than I do about this, but I'll tell you what...

we don't do this on anything that we build where I work :)
 
Hi Michael,
I had some oil canning on the 3 external bays on my left wing. Fortunatelly, I still hadn't riveted the skin on so I was able to correct the flange bent on the ribs and the oil canning went away.

When I contacted Gus@Vans asking for some solutions, he told me that it was just a cosmetic issue that I could leave as it was. Or, if correcting the flanges didn't solved, I could rivet or gluing an L-shaped stiffner (something like the one we use on the inside of the elevator) between the ribs in the affected bays. If you can reach the correct position through the inspection holes, maybe it can be a better solution than drilling out the skins.

Just an idea.
 
Spar flange angle?

Claudio's comment in combination with Steve's comment about "worse near the spar" makes me wonder if the spar flange could be bent incorrectly in the area of your oil canning. I know my spar flanges were all over the place and the skins would've looked like a train wreck had I not straightened the flanges out ahead of time.

Spar flange before adjusting:
20070501-02-tn.jpg


...and after adjusting:
20070501-03-tn.jpg
 
Remember that it is not just the span-wise dimension that you have to worry about, the sheet is also expanding along the cord. Also, since the skin is attached to the spars, not just the ribs rib-flex is only part of the issue.

I wouldn't believe it either if I had not seen it myself.
 
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