Glue for carbon tape

[Matt Piatkowski]

Hello,
For 60" wing, I  need to increase the bending strength of the balsa spars with 1/4" wide carbon tape.
Wings balsa 1/16" sheeting will be glued to the carbon tape with CA and will stretch from the LE to the spars.

Should I glue the carbon tape with CA or with epoxy? Is CA compatible with epoxy?

Thanks,
M

[Steve Helmick]

CA bonds better to epoxy than epoxy does. The CF tape, of course, is epoxy impregnated. Everybody I know (except maybe Howard) uses CA. I'd use CA. The F1A guys use CA, and their wings are stressed way more than F2B wings. Scuff it up and clean it with naptha to get a tooth and get it clean of any parting agent. Steve

[Fredvon4]

Why?   Is your wing design prone to folding in High G?

Think of what you need... and obviously weight vs need.

Almost all CF/Kevlar/FG options are very good in Tension but poor in compression

We need to know wing construction...one central spar  I beam,  or several spars?

I lay my Carbon TOW on both top and Bottom of wing span spars with epoxy slo cure with care taken to reduce glue load....on COMBAT wings

Yes in certain conditions a CA glue under OR over and epoxy glue will work but each needs proper prep

None of my 36 to 60 inch typical stunt wings needs such effort.... evven with run away engine at 3 second laps have I ever FOLDED a normal stunt wing constructed as per plan

[Matt Piatkowski]

Hi Steve, Fred,
This is carbon fibre tape from Dave Brown Products (CFTP-5220), having the width 1/2".
It does not feel like being epoxy impregnated as it is not sticky like typical pre-pregs. The individual fibers move freely and I can smooth, align and separate them relatively easily by finger tips. I used thin CA to attach the 6" long, 1/4" wide piece of this tape to 1/4"x1/4" x 6" hard balsa piece.

I did not sand and did not clean with alcohol the tape before gluing. Then, I glued with thin CA the 1/16" thick balsa on top of the already glued tape. The bending stiffness of this specimen was at least twice of the bending stiffness of the specimen without tape.

Then, I destructively tested both specimens, bending them in my hands until they broke. The balsa specimen reinforced with the carbon tape failed in compression and the specimen without tape failed in tension. The in-plane shear strength between tape and balsa was sufficient and there was no in-plane shear generated separation. Simply put: balsa broke but tape stayed attached to balsa.

Then, I peeled off the carbon tape with 1/16" balsa strip on top and inspected its surface, seeing that balsa was ripped off from the 1/4" x 1/4" x 6" hard balsa piece. This indicates that the tape to balsa CA connection was stronger than balsa itself.

I will sand lightly the tape, clean it with acetone and let it dry. Then, I will spot attach the 1/4" wide x 20" long pieces of it to the central portion of the wing spars. By "spot attach" I mean a single drop of thin CA where the spars to ribs connections are. By doing this, I will secure the tape to the spars but will not fill the entire spars surface with CA. Then, I will attach 1/16 balsa sheeting with pins and fill the entire connection with CA.

The weight penalty will be around 5 grams but I hope the wing will be much stronger in bending.

Best Regards,
M

 

[jfv]

Sounds like you are using CF Tow.  Epoxy works well with tow.