Carbon Fiber

[Richard Miller]

If I were to properly cut and dress the ends of a couple of pieces of CF tube, say 1/8 < 3/16" d., and join them with the accepted adhesive, would I have a really strong joint? And what would that adhesive be?

Totally ignorant about this - Richard

[Dave Robelen]

Hello Richard,
It sounds like you are describing a butt joint. The at would be pretty weak. If you file a mating angle on each end so that you have a longer sloping joint, that will be much stronger. Ideally fitting a sleeve over the joint would also be good practice. Lacking a sleve, I would wrap the joint with a layer of dental floss wound in a smooth layer pulled tight. Medium thickness CA will hold all this together. First glue the tubes and get a smooth joint, then sand any excess glue away before the wrapping. Finally, soak the floss with the CA.
Good luck, Dave

[Vince]

All the butt joints in my kites have an external or internal ferrule. I use a tight fitting piece an inch and a half long, slide it in and use a drop or three of CA to hold it in place. Leaving the other side unglued allows the kite to be broken down for the trip to and from the beach.
What are you using this CF tube for? Maybe we could come up with a good solution if we know what it will be use for.

[Richard Miller]

Dave & Vince,

Thanks. I'll abandon CF tubes and look around for something else. In fact, come to think of it, simple ol' aluminum tube might do.

It's this, Vince. A gull wing: Segment one diverges upward from the fuselage; No. 2 goes out a ways at a shallow angle; No. 3 goes up a little more.

The maximum chord is where No. 1 meets No. 2. If that were, say 4", the chord at the fuselage end would be 3". It gets smaller. I'm thinking area rule and also what's going to look as good as I can make it look.

You can see that this is a bit of a structural problem. I keep worrying it and trying to find the best solution I can. I thought a [very] shallow "U" of carbon-fiber tube, with the bottom of the "U" set in the fuselage, might do it. I am now disabused of that idea. As I say, maybe all I need is aluminum, at least on the current design that has a span of about 30 inches.

-Richard