Oil Canning at lap joint on the wing

Michael Brown · #1 12-06-2009, 07:37 PM

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

Michael Brown · #2 12-07-2009, 08:06 PM

No advice from VAF....

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

Pilottonny · #3 01-05-2010, 02:33 PM

Please see my post here: http://www.vansairforce.com/communit...ad.php?t=52653

Regards, Tonny.

sf3543 · #4 01-05-2010, 03:44 PM

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.

Flying Scotsman · #5 01-05-2010, 10:30 PM

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?).

WingsOnWheels · #6 01-06-2010, 07:09 AM

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.

Mel · #7 01-06-2010, 07:25 AM

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!.

Flying Scotsman · #8 01-06-2010, 10:53 AM

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/Specifi...ssnum=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...

Mel · #9 01-06-2010, 11:06 AM

Quote:

Originally Posted by Flying Scotsman

I don't buy it...sorry...

No Problem!
I just know that I've built more than a few airplanes, and it works for me.

Flying Scotsman · #10 01-06-2010, 11:13 AM

Quote:

Originally Posted by WingsOnWheels

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.

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.