Lower wing skin help

whd721 · #1 11-27-2011, 10:07 AM

I was starting to rivet the first lower wing skin, when I noticed that the skin was not laying flat on the wing ribs. Each dimple was a short column with 1/64th to 1/32nd gap between the rib and the skin. The skin dimple appears a larger diameter than the rib dimple.

This must be the down side of years of delay in construction, and a loss of brain cells.

I cannot remember the tools I used previously, but this time I used a DRDT, Cleaveland Hand Squeezer and Cleaveland Spring Back Dimple Dies to dimple the ribs and skins. I upgraded my tools to do a better job ( Go figgure )

Any tips or techniques I should try?

bruceh · #2 11-27-2011, 10:20 AM

If both the wing skins and ribs were dimpled similarly, they should nest together. The act of setting a rivet will draw them tight.

Also, make sure the rib flanges are still at 90 degrees. If they are not, that will be a problem and it can also contribute to some "oil-canning" of the skins after the skins are fastened.

Vlad · #3 11-27-2011, 11:22 AM

Quote:

Originally Posted by whd721

Any tips or techniques I should try?

William,
Use deburring tool on all rib dimples in question. Countersink just a hair. Also check rib angles as Bruce suggested. You will be fine.

az_gila · #4 11-27-2011, 11:45 AM

Quote:

Originally Posted by Vlad

William,
Use deburring tool on all rib dimples in question. Countersink just a hair. Also check rib angles as Bruce suggested. You will be fine.

Careful on your definition of a hair.

Taking a mere .005 off with a countersink will reduce the thickness and strength by 20%....

I would just rivet a short section on one rib as a test case. As Bruce H. says the act of riveting should draw the skins together.

whd721 · #5 11-27-2011, 06:39 PM

I checked the ribs with a strightedge, they seem square and aligned. I got out the pneumatic rivetor and re-dimpled a rib and its skin line and then dimpled a section of the rear spar and its skin. No change.

I am thinking of moving from a AN426AD3-3.5 to a AN426AD4-4 or a 1/8" OOPS. Thoughts?

The gap is about 1/64th and is only visible with a drop light inside the wing. And then only on the rear spar and outside rib. Maybe I am chasing a ghost?

I will check with Vans tomorrow about the OOPS rivets.

Thanks for the opinions.

Andrew M · #6 11-27-2011, 06:59 PM

William,
I recall working out of an old Convair S.R.M. that actually gave limits for the gap between dimpled sheets. That two sheets don't nest together exactly has never concerned me to much as it is cleco'ed. Once the rivits are in, a lot of that gap will go away, and as long as the skin is not obviously puckered between fasteners, I wouldn't be to concerned about gaps less than .010". The strength of a dimpled joint is much stronger than flat holes due to how they nest. Riviting one rib and having a look would be best.

N941WR · #7 11-27-2011, 07:55 PM

Quote:

Originally Posted by whd721

...

I am thinking of moving from a AN426AD3-3.5 to a AN426AD4-4 or a 1/8" OOPS. Thoughts?
...

I had an IA who specializes in restorations tell me to avoid using OOPs rivets at all cost. He said the short shoulders allow them to pull through. If you are going to redo that area, use 4-4 rivets.

WingsOnWheels · #8 11-27-2011, 08:02 PM

As was mentioned before, set a couple rivets along the rear spar where you have the gap. If this closes the gap then problem solved and build on. Do NOT use shear-head (Oops rivets) for the wing skin. They are ok here and there for a repair, but IIRC the spec say no more than three in a row.

whd721 · #9 11-28-2011, 09:26 AM

Thanks for all the advice.

I am going with 4-4 rivets along the rear spar. It will allow me to re-match drill and re-dimple those locations.

I will order a tungsten bucking bar and a dynaswivel restrictor for the rivet gun.

Any tips on setting 4-4 rivets at full arms length, upside down and by braille?

FlyingArcher · #10 11-28-2011, 10:21 AM

Quote:

Originally Posted by az_gila

Careful on your definition of a hair.

Taking a mere .005 off with a countersink will reduce the thickness and strength by 20%....

I would just rivet a short section on one rib as a test case. As Bruce H. says the act of riveting should draw the skins together.

IIRC, the instructions explicitely tell you to do this (countersinking a "hair") on the rear spar, but not on the ribs that are way thinner.