Joinable foam core wings - RC Groups
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Apr 09, 2012, 03:08 PM
Registered User

Joinable foam core wings

Does anyone have any example of easy to build foam core wings where the two wing halfs are joinable for transportation? I'm scratch building a 72" Super Sportster with balsa sheeted foam core wings, but I'm struggling with how to join them and maintain the dihedral. If it was a flat wing I'd just use telescoping carbon tubes.

Any ideas?
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Apr 09, 2012, 03:30 PM
Bellanca Kruesair
epoxyearl's Avatar
How much diehedral ?
How thick is the wing ?
On a 72" wing,the tube doesn't have to be centered in the core. It can be drilled with the wing set at the proper dihedral ,and still use a straight tube..
Unless there IS too much,or it's too thin.

If you're currently building the wing,a plywood box can be inserted,with a plywood or aluminum joiner installed.
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Apr 09, 2012, 04:40 PM
B for Bruce
BMatthews's Avatar
The old Super Sportster design has a pretty thick wing with some but not a lot of dihedral. So epoxyearl, your suggestion for simply angling the joiner tube so he can use a straight rod or tube to join the halves is a fine way to do the job.

Chris, you also need to get the loads from the joiner and slip tube to connecto to the outer skins or you'll be depending on the foam to resist the bending loads. And that is NOT a good idea. For the root ribs on each side use 3/32 or 1/8 ply to connect the tube to the skins. For the outer end of the slip tube where the joiner rod or tube ends you can cut a slot through the wing top to bottom and insert a half rib of the same plywood to again join the tube up to the skins. For a 72 inch wing which likely has a 10'ish inch chord I'd suggest that this half rib be about 4 to 5 inches long but leave the leading and trailing edge foam alone so it doesn't mess up the alignment when you skin the wing halves. Or alter it as you see fit if you use these two plywood root and outer ribs to also serve as mount hardpoints for the landing gear wire blocks. A piece of roughly .070 x 3/4 OD carbon or some 6061-T6 aircraft tubing would make for a nice joiner for your wings.
Apr 10, 2012, 12:07 AM
Registered User
Thanks! This helps alot. It's the old Super Sportster, from old RCM plans. Going foam core to save on some balsa. Looks like each wing tip rises from center by 1.5". It's a 13" chord (13 and a horseshoe or handgrenade) and 2" at it's thickest point on the airfoil.

How far into each wing panel should I make the tubes go (how far from center should I make the half-rib)? I imagine I'll need well over a foot if I want to distribute the loads well, but I'm totally guessing. Any guidance there?
Apr 10, 2012, 12:46 PM
B for Bruce
BMatthews's Avatar
The wing joiner would be fine with a mere 6 inches between the root and outer ribs that support the slip and joiner tubes. The skins you apply are what actually holds the loads. If you want to use the outer plywood sub rib to aid in supporting the landing gear mounting block then go with the sort of spacing you need to accomplish that task.

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