Carbon tow source???

[SaltyOne]

I'm trying to reinforce the spar on an old Oly II. I want to glue carbon to the bottom spar caps. I've seen carbon that looks like tape. It came in my Gambler kit. I don't know if it is called "tow" or something else. At any rate, I am hoping that some can point me in the right direction to find a source for this kind of product. Any help is appreciated. Thanks.

George

[ozmo01]

cstsales.com also known as the composite store.

[12ten]

"Tow" refers to unbraided/twisted continuous filaments. The number (3k,6k, etc) tells how many fibers.

The stuff in the Gambler kit has a webbing binder sprayed on. I believe this is it:

http://www.cstsales.com/heat_tack.html

If you don't want the webbing just get regular tow.

[12ten]

...oh and here is a link you might be interested in:

Strengthening built-up wings (http://www.ppssrc.com/articles/carbonwing/carbonwing.html)

[williamson]

The attached files tell you the basics of adding carbon fiber to wing spars.

[SaltyOne]

Thanks for all the help everyone. I especially like the instructions on how to do the project. The one thing I don't understand is why you would laminate carbon to the top spar. The top spar is in compression, and I wouldn't think that unidirectional carbon tape would not add any strength in compression. I'm sure it has a lot of strength in tension, hence adding it to the lower spar is useful. Any arguments for adding it to the top spar?

I'm also going to order some Kevlar thread to wrap around most of the spar. Do you think this should be done before adding the carbon or after (i.e under the carbon or over it). I was thinking if it goes over the carbon it may cut into tape and reduce its effectiveness.

Also any ideas on strengthening the joiner rod area. The rod looks to be about 3/16 music wire. Something in carbon may be an option in this area as well. Thanks for the bandwidth.

George

[sekollera]

I sell ya a 300' roll of carbon 12k x 2 strands (600' total) for $30 shipped. Shoot me a PM.

/Adam

[jcpatrick]

. . . The one thing I don't understand is why you would laminate carbon to the top spar. The top spar is in compression, and I wouldn't think that unidirectional carbon tape would not add any strength in compression. I'm sure it has a lot of strength in tension, hence adding it to the lower spar is useful. Any arguments for adding it to the top spar?

I'm also going to order some Kevlar thread to wrap around most of the spar. Do you think this should be done before adding the carbon or after (i.e under the carbon or over it). I was thinking if it goes over the carbon it may cut into tape and reduce its effectiveness. . . .
Carbon fiber is stronger in tension than compression as you say, but that's irrelevant because . . . it's stronger in compression than any other light-weight material. A lot stronger than other materials. It's stiffer than any of them too*. The normal recommendation is to have the top spar-cap be twice the thickness of the bottom spar-cap to make up for the 'weaker in compression' aspect.

Once assembled together, wrap it with aramid/Kevlar® tow or thread to keep it from separating under pressure. Then put a thin layer of balsa on it so that iron-on coverings can stick.


*Boron fiber —actually tiny rods of boron about one hair diameter— is stiffer than carbon fiber by far. But it's unavailable, cripplingly expensive when found, and dangerous as can be. Think of a hair stiff enough that it can and will pierce your hand.

[SUNSQUINT]

check out this thread (http://www.rcgroups.com/forums/showthread.php?t=564940&page=3) I had posted on capping ribs, good stuff from several people.

What I think you maybe looking for is I was all set to do a wet bath roller system for pulling tow, but ran across is a Dave Brown Carbon fiber strip product I found at my LHS....so i gave it a try since it was something that would be much more available to the average guy and easier to work with. It is Part # CFSP-5230.

The strip is a pre-cured ribbon of unidirectional fibers (just called uni) and measures .007" x .500" x 66". It was $7.50 for the package and is enough to conceivably do an entire model. It proved to be good quality and easier to work with than I expected.

I am a comopsites tooling and process engineer and and have about a mile and a half of 3k and 6k tow if that is still what you are looking for....

[T.D.]

"I'm also going to order some Kevlar thread to wrap around most of the spar. Do you think this should be done before adding the carbon or after (i.e under the carbon or over it)."

Wrap the Kevlar over the carbon. Don't go crazy with the Kevlar, you don't need to completely cover the spar..it can be spaced a bit and since you are adding the carbon to an already built wing you don't want to make a big bump on the spar surfaces so it's a good idea to take some tows, wet them out and press them (or vacuum bag them if you have one) let them cure and apply. Then wrap with Kevlar. This assumes that you are adding the carbon to the outside of the existing spar caps...are you?

"Also any ideas on strengthening the joiner rod area. The rod looks to be about 3/16 music wire. Something in carbon may be an option in this area as well. Thanks for the bandwidth."

This is where you want to make tight wraps with the Kevlar (or wetted out carbon tow) but remember you are limited in how much strength you are able to add by the wing rod. Also weight adds up quickly...

BTW, I highly recommend the carbon tow that sekollera sells.

"The normal recommendation is to have the top spar-cap be twice the thickness of the bottom spar-cap to make up for the 'weaker in compression' aspect."

Unless the spar is sized for stiffness in which case both caps are the same thickness.


T.D.

[dhaverlah]

All good stuff here. The carbon strength in compression is only applicable when the fibers are encapsualted in an appropriate matrix, i.e. epoxy or bmi etc. If you are talking about raw carbon fiber, you can't push a rope. :rolleyes:

As said, don't wrap too much of the Kevlar, space your "stitches" about .1-.2 depending on the underlying structure.

SUNSQUINT, I figured you'd be in on this one. Hope you have a good weekend.

[steelhead]

Carbon Tow is available on my wesbsite-


For 100 or 200 foot lengths of 3K, 6K or 12K Tow click here-

http://www.steelheadproducts.com/carbontow.htm


Or if you want a sample pack of all three for $5.00 (including shipping)-

http://www.steelheadproducts.com/Specials.htm



Dean