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Reinforcing Wing Spars with Carbon Fiber

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Old 09-26-2002, 07:57 PM
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JDHammer
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Default Reinforcing Wing Spars with Carbon Fiber

Hi, here's my example: 84" wingspan, 22lb, all wood, built up unlimited aerobat. You want to strengthen the spruce spars with carbon fiber tapes running along the spar.

Questions: Best way to bond CF to spruce (CA?). And also, where to apply CF (Top and Bottom?, Front and Back?). One more- thickness of CF for the aircraft example above? (Assuming we don't want to add too much weight.)

Wonder how many "Gs" this aircraft could absorb after being properly reinforced?

Thanks for the help, JD
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Old 10-02-2002, 11:33 PM
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R. Carver
 
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Default Reinforcing Wing Spars with Carbon Fiber

Well, since no one else has answered yet, I'll step up...
Use the carbon strips on the top of the top spar and the bottom of the bottom spar. I'm thinking around .010 on bottom and .020 on top, thicker on top because CF and spruce are weaker in compression than tension. Glue it on using a good laminating epoxy like West Systems. Use balsa end-grain as shear webs between the spars. Wrap the spar assembly tightly with kevlar tow spacing the wraps about 1/8" towards the root, 1/2" towards the tip. Brush a thin coat of the epoxy over the whole thing.
Build it like this and the stab will fail before the wing does
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Old 10-03-2002, 03:03 AM
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JDHammer
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Default Reinforcing Wing Spars with Carbon Fiber

Thanks R.C. , that's exactly the information I needed. Sounds like you could use the wing for a diving board after that treatment. I'll give it a try.
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Old 10-03-2002, 10:39 PM
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Default Reinforcing Wing Spars with Carbon Fiber

R. Carver seems to have a good system.

I can only make one comment, use the lightest weight balsa square stock that you can find for the spars instead of the spruce, and put one layer of the uni tape on the top and bottom of each of the spar.

Then continue with R. Carvers method, just go very lite on the epoxy!!! This is still overkill, but it will be very light and you will be battling weight with a bipe.

My 2 cents,

Darrin C
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