Carbon Veil

I've heard a lot about carbon veil as a finish substrate for models, but I haven't seen it in use or talked to anyone who has actually used it. Is carbon veil the same as carbon mat I see advertised? If not, where do I find it? What is best to apply it with, epoxy, finishing resin? I assume it is primarily to add stiffness/rigidity to the structure without adding substantial weight.

Any guidance you can give me will be appreciated.

Just dope it on like you would silkspan. Then you can either use a talc or similar filler on it like you would if you had used silkspan or you can sand it and let the carbon fiber mat become the filler. You will need to recover when you do this, however, and it takes quite a bit of the carbon mat (more expense).

The carbon mat will add a little stiffness, but you can use it only over solid wood. You will still have to use silkspan over the open bays.

The material you want is "soft" matt from ACP. "Hard" matt will not work very well at all, and result in many pinholes.

On your plane that is cracking, did you put silkspan on the wood, or just paint over bare wood? Matt has been using silkspan lately over the majority of the fuselage, but puts carbon fiber "patches" down in the stress areas (Behind the wood canopy, where the trailing edge of the wing joins the fuselage, leading edge of the stabilizer...) If put over the stress areas, it reinforces these without a need to go "all the way". It doesn't appear that the .2 ounce carbon fiber veil is going to be any stronger on the fuselage than a single layer of silkspan. It may be stiffer, if that is important. Gieseke thinks it is lighter, but then he uses just the carbon fiber for filler...sands it off...reapplies. You can get a good, light finish either way, but when building light, reinforcing the stress areas before they crack can be important.

Most likely just an error in processing the order. Save the 0.5 oz material for doublers, and order some more of the 0.2 oz stock.

>) She said they only
>carried one kind now, I
>wonder if the .2 ounce
>is no longer available? Anyone
>know?

I placed and received an order for the 0.2 oz/sq yd material in December. At the time, I told the nice lady that took the order, that I understood that there were two types of 0.2 oz material available. She said that "Mr. Fancher" recommend the more flexible of the two, and that was what they were currently offering. They do have an 800 number, so you can check to see what is available.

As far as weight is concerned, I use the 0.5 oz/sq yd material under nose doublers, but I find that it absorbs an enormous amount of epoxy if you want it to be throughly "wetted" through. It took approximately 12 cc of epoxy per side to fully saturated the carbon fiber between the fuse side and the doubler. If you use the 0.5 oz material for covering the fuse, not only is it 2 1/2 times heavier, it will also take considerably more finish to fill it up.

Cheers,

Warren

ps: Nils, you sure got a lot of "press" in the last copy of Stunt News. Can I get an 'electronic autograph' ? <g>

Nils (electronic autograph for Warren )

"Hey goys,
I've heard a lot about carbon veil..."

I always suspected that that stuff isn't kosher.

>
> I always suspected that that stuff isn't
>kosher.

Himmel! Comes off of a pig, maybe?

K.

P. S. Talk about slow on the uptake! It was at least a day after seeing Howard's "kosher" comment before I realized he wasn't directly going to "veal" from veil. I'd been overlooking the "goys" in the subject line all along . .

Glad I stumbled onto this thread. I have sort of a proprietary interest in this stuff since for some time I've been advocating its use. I still do, but with the caveat that you should be very careful for a while to insure that you get the right stuff!

First, let me say that George and Barbara Spahr at Aerospace Composites couldn't have been more helpful and forthcoming on our needs in the CF veil department. They are very anxious to please us and have gone out of their way to be as accomadating and helpful as possible.

That said, however, ACP is merely a retailer of goods they get from their suppliers. They don't actually produce any of it and are, therefore, at the mercy of changing times and changing moods on the part of those suppliers. We have spent some considerable time ironing out the pluses and minuses and the various suppliers to insure that they stock and are familiar with precisely the material which does the jobs we stunt people need.

To short curcuit a long story, they now have available and are familiar with precisely the product we prefer. It is currently in stock and available for shipping. As a previous contributor mentioned, they now have "only" the soft version acceptable for finishing purposes as outlined earlier. Although this "soft" version is 10% less desireable for purposes such as doublers, internal reinforcement ,etc. it is perfectly adequate and, given the fact that it makes such a great finish undersurface, more than qualifies as "the" CF veil to use.

In the interim, until we are all trained to recognize the "right" stuff, when we see it here's what to look for.

The right material is black (big surprise), soft to the touch rather than brittle or "starched" feeling and has a non-uniform appearance. The appearance giveaway is random strands of noticable larger fibers scattered about.

The bad stuff, on the other hand, is very uniform in appearance-more like black tissue-and has a starched, brittle feel to it.

In use the differences are immediately apparent. The binding material in the good stuff softens with dope and allows the fibers to "readjust" their position relative to one another. This makes it reasonably flexible in covering compound curves and shaping around the edges of surfaces such as elevators, tails and flaps etc. It will fill with just a few coats of dope and a couple of filler coat to an impecable finish.

The "bad"stuff remains stiff with the application of dope and has almost no ability to form around edges and corners. (This is the one characteristic which makes it preferable for purposes like doublers, etc. It acts pretty much like a very thin piece of plywood...with all the flexibility inherent in that description!) Even worse, when used as a finish undersurface it is almost impossible to fill completely. It will leave gazillions of tine pinholes that seem impervious to any known method of filling. It is ugly and evil in these uses and should be exorcized at all costs! I think that pretty much says it all.

Oh yeah-

Ted, I used the hard .2 oz stuff with the Balsarite brushed over it, sanded that & shot on two wet coats of PPG waterbase primer. I sanded most all of the primer back off & shot it with a rattle can. No pinholes at all. Maybe the Balsarite fills the little buggers or melts the binder? I didn't even realize there was a shiny side & a dull side until I was halfway through the job & Scott Riese pointed it out to me. Didn't seem to matter. Btw, I'm a bodyman by trade & I know a pinhole when I see one, they are the Bain of my existence

"Order Desk: (800) 811-2009 Technical Assistance: (510) 352-2022"

I think Nils is onto the answer. In order to create a proper composite matrix ie fiber and epoxy(generic), it is important for the binder to be broken down by the solvents in the epoxy, dope, polyester, etc. If this binder release does not take place, as described by Ted, then there are great numbers of voids created in the matrix due to the suface tension and "wetability" of the material--the result in this case is lots of pinholes cosmetically--more important is lack of proper strength development.

In the example Ted indicates for making doublers and other flat structural reinforcement, you will find that there will be MUCH less strength developed in the hard binder samples until a bonding material is used that will release the binder.

My experience with this hard stuff is that both epoxy, and dope failed to break down the binder. I suspect that styrene in polyester might be the stuff it is designed to be used with. The heat that Nils used probably did it temporarily, but again, for a proper matrix to develop, the binder must be chemically soluble in the bonding material.

Its mighty expensive stuff to use for only cosmetic reasons.

FWIW

The carbon fiber may make the structure stiffer, however. Certainly if it were epoxied on it would be (but it would also, then, be heavier). More tests certainly should be done before definitive conclusions are made. If you take a bare flap and twist it, you will notice that it will be fairly flexible unless made of extremely hard wood. If you take the same flap and cover it with the carbon fiber veil doped on, it will now be considerably stiffer. However, the same (or equal) flap covered with doped on silkspan will, also, be considerably stiffer (than the bare one).

I don't know which would, indeed, be stiffer or by how much, but one of the problems with the veil in adding the stiffness that carbon fiber is noted for is the randomness and shortness of the fibers.

For controlling twist in a long slender flap, the proper material might be two layers of unidirectional layed at a 30 degree bias. Or a piece of .75 Oz flat woven fabric cut and layed at a 45 degree. ( The same way you might orient balsa grain in a laminated panel.)

The trouble is, like you said, the weight can go up fast. I came the conclusion that this would be an appropriate application for maybe a built -up sheeted flap with very thin skins and a CF wrap. Once the CF skin is used, all of the bending and twisting loads become tension in the skin, and compression in the core (monocoque) so applying this stuff over solid parts becomes heavier than required. Alot of the core function is to simply maintain the spacing of the stressed skin. (and I'm sure the structural guys here will call me to task for not mentioning the core-to-skin shear as well)

Used in that way for hollow stab/el, built up flaps, and light fuse sections really makes sense, even with epoxy. But getting high fiber content ratios is nearly impossible to do without vacuum bagging. Otherwise, painting on epoxy and trying to remove excess or sand off weight is not very effective overall.

Also, the difference in strength or stiffness between reinforcing with .5 or .6 oz CF versus regular old glass fiber of same weight can be difficult to evaluate or take advantage of unless very consistent and optimum fiber content ratio can be created--nearly impossible by hand.

Another real problem with CF over balsa is that, even with small amounts the skin becomes so strong that in bending, the core simply crushes. The popular full-scale solution is to use end-grain balsa for core since it is quite strong in that orientation. Also, since usable layup thicknesses are so thin for our purposes, small process variations in fiber content or thickness can create very big stress concentrations and these also can lead to core failure.

All in all though, carbon fiber is a wonderful product. It does take alot of insight to optimize its potential however.

Having been involved with fiber reinforced composite engineering, design, and application for thirty plus years, I actually got to see the introduction of Kevlar, carbon fiber and some others.

Anyone for synthetic saphire or silicon carbide fiber reinforcement?? Yes, its out there.

just some thoughts.

I'm glad to have these forums to discuss some of this stuff--its hard to find other concentrations of modelers interested in these things.

The article you are refering to was written by Don Hutchinson, and published in the Sep/Oct issue of Stunt News. He did a good job of designing some simple tests and he presenting some very interesting results. Don has an engineering background.

His finding were objective (as opposed to subjective), based on actual measurements of the test sample that he produced. Basically, his conclusion was that there was very little diffence in strength and rigidity between balsa covered with carbon veil or standard silkspan. Please re-read his article for the exact details. Well worth the read.

Cheers,

Could someone please specify by ACP Code which of the material should be ordered?

Thanks