I've been dragging my feet on answering these questions because of general laziness and also because I don't want anyone to think I'm trying to say you should be using this material on F1D spars. It's a material that most people have never seen and I think it's interesting. Here's a brief description of the material and a quick experiment I did.
(tow is just a bundle of fibers)
The uni-directional fabric is pure carbon. It has no epoxy. It's made up of very small tows that all go in the same direction and has crosswise threads woven in about 1/4" apart to hold it together. You can separate the tows at the edge of the fabric by just pulling the outside tow away from the fabric for whatever length you need.
It's these separated tows that weigh about 8 mg for 24". They are pretty fragile. If you try to coat a tow with glue by rubbing the glue on or by pulling the tow through a saturated tissue or cloth you will just strip off fibers from the tow until there is nothing left. To get a little more rigidity in the tow and to keep it from coming apart I attached a small blob of clay to one end and then held it up by the other end and sprayed it with a couple of coats of clear lacquer. After doing this the 24" length weighed about 10 mg.
Then I took a 12" piece of spar wood and glued the tow to the top and bottom of the spar with a lot of thinned Duco. The Duco has been sitting around for a long time and was not all that thin. The bare wood weighed 41 mg and then weighed 59 mg after the carbon was glued on. I think a better way to use this tow would be to spray it until it was pretty stiff and then use acetone to adhere it.
I've been using this tow in an X pattern to reinforce wings on Cat 1 gliders. I haven't tried it as a spar reinforcement. The wing in the picture has lightweight tow from Mike Woodhouse in the spanwise direction and the super light russian tow making the X pattern.
----- Original Message -----
From: Mark F1diddler
To: Indoor_Construction_at_yahoogroups.com
Sent: Wednesday, January 05, 2011 10:22 PM
Subject: [Indoor_Construction] Re: Boron / Carbon
--- In Indoor_Construction_at_yahoogroups.com, "leop12345" <leop_at_...> wrote:
dI do not know how much glue is needed to hold down the boron fibers (I hope to remember to weigh a wing spar before and after sometime). Maybe Mark or someone else knows.>>
Not I! It's a personal thing according to how firmly you want it attached. Whatever glue % weight I suggest, someone else will say they use half that weight in glue, and I wouldn't doubt they do. I used to figure on about 50% of the boron's weight in glue, believing that boron *had* to be well attached all along a spar. But now believe if the boron is not buckling in the other direction (fore to aft) and it's at least attached along most of the spar's length, the boron still seems to function as a "rigging" of sorts even where not firmly attached. (Of course talking parallel spaced boron pairs here.)
> The bottom line, in my amateur opinion, is that boron fibers are the best stiffener material available for indoor planes at the current time.>>
Prolly so, and I wasn't being rhetorical in asking Bill--how do I separate a consistent strand of carbon from carbon fabric, weighing 8 mg per 24"? I have some .004 uni-D carbon, but from 1999. Will that do, Bill?
Mark F1diddler
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Received on Wed Jan 05 2011 - 22:29:03 CET