Wing sheet joints - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 01-21-2021, 08:45 PM   #11
Edge540
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Quote:
Originally Posted by michaely View Post
Quote:
Originally Posted by Edge540 View Post
Here is Carden's layout for clarification and here is my new lightened core
Sorry to be a nerd but the wood joint you have in the second picture is not a scarf joint but a square edge to square edge joint at least some of the glue joints being diagonally across the face of several planks of wing sheeting - the diagonal cut presumably marginally avoids a glue edge falling on a larger percentage of the wing core where the lightening circles in the foam core are located.

For an image of a classic scarf joint - without any interlocking hooks - see the center image in the third row of this collection of scarf woodworking images:
https://www.google.ca/search?sxsrf=A...w=1024&bih=710


But on the larger issue: a square edge to square edge glue joint along the side edges of balsa sheeting is quite strong (but end grain to end grain glue ups are weak)

I don't think such diagonal glue joints across the face of several planks in your situation make any significant difference in the strength of joints/structure and are an "unnecessary" waste of balsa.

I've made fully balsa sheeted wings, stabilizers, etc. over a balsa rib and spar skeleton - using several balsa planks glued side edge to side edge without any issues.
Even more common are balsa sheeting of the aft fuselage where not all edge to edge glue ups fall on a fuselage stringer/longeron.
Yes, I will take advantage of any spars/longerons to have edge to edge joints to fall on such timbers and have that backing support but I wouldn't adding any batten support to such an edge to edge glue joint for that purpose alone.
The covering further strengthens such a joint.
Don't think you understand the second picture. The angle you see is just the trialing edge of the wing cut. Has nothing to do with gluing edge to edge.
The butt joint is the added 6.5 inches that I'm saying a scarf joint would be better.
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Old 01-22-2021, 10:19 AM   #12
Edge540
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Quote:
Originally Posted by stegl View Post
Got a friend here that does a zig-zag lazer cut to join sheeting . That way not a lot of waste and the strength is proportional to the surface of the glue joint. This us in 2 inch and wider sheeting. As for narrower stuff , like sticks for spars , the scarfe works better.

Doug , presume that foam lightening is CNC routed ? Looks great . How do you glue the sheeting ?
The honeycomb was all hand cut. Roughly 800 of them. The templates were CNC lasered and made from Bristol board. The sheeting will be glued on with polyurethane glue applied with a small roller over the honeycomb.
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Old 01-22-2021, 01:44 PM   #13
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Re: Wing sheet joints

What I watch for, given the choice, is to avoid any end to end joints in the center 50% of the wing, so that the sheeting towards the root of the wing has uninterrupted spanwise grain. With the loads diminishing towards the tip it doesn't worry me as much.
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Old 01-22-2021, 01:47 PM   #14
Edge540
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What I watch for, given the choice, is to avoid any end to end joints in the center 50% of the wing, so that the sheeting towards the root of the wing has uninterrupted spanwise grain. With the loads diminishing towards the tip it doesn't worry me as much.
Yes both close to the root and close to the tip have the least load. The biggest load is likely at the end of the wing tube.
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