Removing Wood Wing Skin From Wood Rib

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C.D. Donald

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I've acquired a Cassutt that hasn't flown in over 15 years. Somehow, I managed to damage the skin over the second innermost rib. So I need to remove the skin from the root to the second rib; my plan is to scarf the 1/16" plywood skin over the third rib and replace the skin.

But how best to remove the skin over the inner ribs? I've been searching online for a week and haven't come up with a good solution - does anyone have a suggestion? I have one idea, but I'm not sure it's the best way.

Hopefully, my question makes sense.
 

lr27

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Do you know what kind of glue was used? Many kinds of epoxy soften enough with heat that you can separate them. It might take less than 100 C. I don't know if that weakens what's left, though, and that might require some homework.
 

TFF

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Cut out damage areas between ribs as needed then sand off the ply from the ribs. If the damage is small, you might be able to do a round, like a silver dollar, scarfed repair.
 

C.D. Donald

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First, thanks for the replies - they're genuinely appreciated.

The damage is most of the length of one rib. The skin is mostly cracked from the spar to the trailing edge on both sides of one rib (the second rib closest to the fuselage). The skin is also cracked ahead of the spar along that same rib.

I don't have information about what glue was used, but I'll investigate.

It appears to me that I'll need to replace the skin from the inboard edge to the third rib - about 18" wide and from the leading edge top to the trailing edge. I'm considering cutting the skin off and then using a sander to bevel the skin on top of the third rib to an acceptable scarfing degree.

Getting the skin off the first and second rib without damaging them will be a good trick.
 

TiPi

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I have taken ply sheeting (3mm) of a fuselage (wood stringers) like this:
use a multi-tool with a wide cutting blade and cut along every stringer
using a sharp Stanley knive with a solid blade (fixed blade), cut from both sides between the last and second-last ply (on the stringer side)
lever off that part of the ply (or use a very sharp wood chisel)
sand down the remaining ply to the stringer
Cutting the ply down to 1 or 2 layers speeds up the sanding process

I also replaced the top wing skins (1.2mm). As they were on foam ribs and composite spars, I simply cut all the ply along the rib and spar lines and added the new skin on top of the remaining skeleton.

In your case, you would need to start cutting in the centre of the rib bay and work your way to the ribs and spars.
 

C.D. Donald

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I have taken ply sheeting (3mm) of a fuselage (wood stringers) like this:
use a multi-tool with a wide cutting blade and cut along every stringer
using a sharp Stanley knive with a solid blade (fixed blade), cut from both sides between the last and second-last ply (on the stringer side)
lever off that part of the ply (or use a very sharp wood chisel)
sand down the remaining ply to the stringer
Cutting the ply down to 1 or 2 layers speeds up the sanding process

I also replaced the top wing skins (1.2mm). As they were on foam ribs and composite spars, I simply cut all the ply along the rib and spar lines and added the new skin on top of the remaining skeleton.

In your case, you would need to start cutting in the centre of the rib bay and work your way to the ribs and spars.
TiPi,

Thanks for your thoughts, they're very close to what I've been considering starting with the multi-tool (oscillating tool).

To produce the scarfing (beveled) surface on the 1/16" skin, I'm planning on using a belt sander with a shim (of sorts) affixed to one side of the belt sander to lift or tilt the sanding belt to 8 degrees - about an 11 to 1 ratio which should be acceptable for a scarfed joint (generally a 10 or 12 to 1 ratio). If it works on the wing skin, it should be easier to duplicate on the flat replacement stock.

Thanks again.

CD
 

TiPi

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I use an alu rail with a slot (solar panel rail), then made a sanding block that has the lenght to get the 12:1 ramp when one end is in the slot and the other on the sheet. The rail is then clamped over the ply sheet at the correct distance from the edge and acts as a guide for direction and height.
For anything where I can't use that system, I run a pencil line that represents the 12:1 ramp and use a flat sanding block to sand the ply edge down to a feather at the edge and on the line at the same time.
Use top-quality 40 or 60 sanding paper and scarfing is a breeze.
 

VP1

Todd C.
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I've removed 1mm ply from a few bits of structure during my build. I've found an 80 grit flap disk chucked into a hand held grinder works extremely well for removing ply. Easily controllable and not overly aggressive.
 

VP1

Todd C.
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Personally, for scarfing thin ply like 1/16" I don't bother with any setup. I use the above mentions flap disk to sand a nice bevel into thin sheet. Goes quick and is easy.
 
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