Wing skin fitting question

[Charles in SC]

I am fitting the bottom skins on my qb wings. The skins were about a half a hole from lining up so I aimed my shop heater at it for about 10 minuets and they fit pretty good after that. My question is, is it ok to warm the skin like that and then rivet them on. I have done this with other projects such as bus siding etc and everything was fine but the wing structure is much more frail.
Could it warp when the skin cools back off. I did not heat so hot that you could not hold your hand on it maybe up to about 85 or 90 degrees.
Thanks for any advice!

 

[Mel]

Absolutely no problem heating the skins while riveting.

Several of us "early" builders used this method. It makes the skins "drum" tight.

 

[DB1033]

We had the same issue on both wings

We were finally able to get the R/H skin/spar holes to line up thru some creative clecoing. We thought we were good to go until we laid the wing on the bench and noticed that 2 bays on the upper outbd skin (1st 2 bays outbd of skin splice) are now loose. You push in on one bay and the other one oilcans up...and vice versa. I'm almost certain that this will oilcan in flight. At the very least it will be annoying and at the worst be a fatigue issue.

Does anyone have any experience with anything like this?

Our initial thought is to locally stiffen those bays (we can acess them thru inspection panels) using some angle.

I'm concerned because the L/H wing has the same mismatch the R/H wing had...except more severe. I'm worried that we may encounter the same problem on the other panel once we "finesse" the skin into place.

Any thoughts?

 

[Flying Scotsman]

Several of us "early" builders used this method. It makes the skins "drum" tight.

I have to ask about this...not to argue, just wondering...

Let's say aluminum has an alpha of (from what I could find) around 23x10^-6 m/m/deg C (more or less).

To keep it simple, let's say a wing skin is 3m.

If you heated it up by as much as 20 C, that would give

20 * 3 * .000023 = .00138m increase in length. That's about 54 thousands of an inch. Over the entire length of the skin (assuming 3m).

Would that really cause the perceived/observed effects when the thing cooled down? And if it did, wouldn't it put a bunch of rivets in a prestressed (shear) condition that shouldn't be?

Not an ME, just wondering because I've heard this several times now...didn't need to do it, my prepunched holes all lined up nicely and the skins look just fine to me

 

[Noah]

Let's say aluminum has an alpha of (from what I could find) around 23x10^-6 m/m/deg C (more or less).

To keep it simple, let's say a wing skin is 3m.

If you heated it up by as much as 20 C, that would give

20 * 3 * .000023 = .00138m increase in length. That's about 54 thousands of an inch. Over the entire length of the skin (assuming 3m).

Would that really cause the perceived/observed effects when the thing cooled down? And if it did, wouldn't it put a bunch of rivets in a prestressed (shear) condition that shouldn't be?

Not an ME, just wondering because I've heard this several times now...didn't need to do it, my prepunched holes all lined up nicely and the skins look just fine to me

You are right! Although these are the same material they have initial different temps and when they get to the same temp the stress will need to go somewhere! It will be reacted thru the rivets.

 

[mcencula]

Yup.

<snip>

Would that really cause the perceived/observed effects when the thing cooled down? And if it did, wouldn't it put a bunch of rivets in a prestressed (shear) condition that shouldn't be?

If the skin is 20 degrees C warmer than the substructure when it's riveted, and assuming the holes line up perfectly during riveting, then after it all cools to a uniform temperature the rivets will indeed be in shear. The shear force would be the same as the amount you would have to pull on the skin "stretch" it .054 inch. Whether this would be a problem for the strength or longevity of the wing is a question that would be best answered by Van's.