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Building Tips and technical articles. => Building techniques => Topic started by: Clint Ormosen on October 13, 2007, 01:31:28 AM
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I seem to have forgotten about the flaps while doing the finishing on the Mustang. I have them made and hinged but I didn't dope or tissue them yet. I have some .3 ounce carbon tissue I wanted to try on something. Seems this might be a good place to try it. Will it help keep the flaps from warping? Can't I just dope the stuff on with nitrate? Does it fill faster than silkspan? Any suggestions here from someone that tried it?
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HI Clint,
I have used .2 CF veil on flaps several times, using Nitrate to put it on and fill it. I had zero problems, but Kent Tysor has some problems of pin holes. I don't know what Kent applied it with.
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I did no know of carbon in such thin tissue. is it woven? are there some good pictures? How expensive and where?
I take it that this is used purely for strength and not covering open areas, right?
Sorry about so many questions all at once.
Robert
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Clint,
I put 3 coats of nitrate down first to seal the wood, lightly sanding between coats. I then cut the veil to size and positioned it over the flap and applied thinned nitrate thru the veil to attach to the flap. When dry applied 2 more coats of nitrate and lightly sanded between coats. Now your ready for primer.
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I did no know of carbon in such thin tissue. is it woven? are there some good pictures? How expensive and where?
I take it that this is used purely for strength and not covering open areas, right?
Sorry about so many questions all at once.
Robert
Hi Robert,
As to "woven", no. I don't have any pictures handy, but the veil looks similar to heavy Silkspan, sorta. Slightly stronger than silkspan, but much "harder" when it's finished. And it depends on what you use to apply it. You can use dope, or thinned epoxy, or Z-Poxy, etc., to apply it. Doesn't shrink, on it's own, of course, and I have not seen where dope will cause it to shrink either. I see it used sometimes in place of fiberglass cloth, but I do not *believe* it is as *strong* as fiberglass, in this scenario.
Expensive?? that depends........ it costs a good bit more than silkspan.
Randy Smith at Aero Products provides it, and there are other online suppliers.
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A couple of suggestions... I haven't found it necessary to precoat the surfaces with dope prior to laying on the carbon veil. Sand it out to final shape with 400 wet or dry and apply the veil direct. The stuff comes in 2 types, sized with what acts like wallpaper paste, and unsized. The unsized is difficult to cut and handle as it shreds easily. The sized is easy to handle, but takes a few reapplications of dope before it softens enough to adhere closely to the surface. So use acetone to stick it down and dissolve the sizing, and then dope over the acetone right away. Gives good adhesion and quicker application. Tom Hampshire
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Thanks to all who replied. I think I'll give it a try.
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Clint,
One caution. If they are relatively thin flaps, do your self a favor and use low shrink dope to put down the carbon veil. The high shrink stuff can turn them into pretzels.
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Robert: This is it, I have purchased from RSM and Randy.
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Carbon tissue sucks! I never got around to trying it on the Mustang flaps so I thought I'd try it on the Chipmunk elevators. The stuff comes apart the second you touch it with a brush or finger. I was using thinned nitrate dope. I even tried putting the dope down first and laying the tissue into it. No good! Maybe you could spray dope over it but if you touch it with anything, it acts like wet toilet paper. Lame.
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Hi Clint,
Please give us the info on where you got that stuff so we won't! I have never heard of this problem, seriously. A lot of us have used .2 oz. carbon fibre veil on a lot of planes and never had it fall apart. Sounds like you have something completely different.
Bill <><
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Don't give up. Got mine from Aerospace Composites. Look for MATS
http://www.acp-composites.com/acp-mats.htm
MC-01 .2 oz Carbon Mat 35.5" x 1 Ft. $4.25
MC-02 .2 oz Carbon Mat 35.5" x 4 Ft. $14.75
MC-03 .2 oz Carbon Mat 35.5" x 9 Ft. $25.00
Remember you can't paint it on like silk span. If you use the painting motion you will cause it to separate. You must dab it on carefully. I know the stuff Randy Smith sells is also good as he includes it in some of his kits and there has never been a problem with it. The first coat takes a little patience to get it stuck down. After that it's a piece of cake. The nice thing about the veil is that you can manipulate it around shapes much easier than silkspan....Good luck
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Sounds great.
Looking at the cowl covered with it makes me ask it this would be good to layer on top of flimsy (rather thin) fiberglass to stiffen it?
Robert
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Hi ,
Do you finish over th CF veil with silkspan ?
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Hi, Ty!
What relatively little experience I have over 60 years of covering model aerioplanes leaves me with this... (BTW, first covered model was a 10 cent Comet rubber scale jobbie. No tissue in the kit. Tissue specified for covering. Only tissue in the house was "bathroom tissue." Yes, I did...)
Build a surface of Nitrate on the wood (two or three coats, sanded if necessary to reduce fuzz; first coat about 50/50 thinner/dope - later coats thinned more.) Smooth the covering over the side to be covered. Wick THINNER ONLY through, around the edges, to soften the dope which will adhere the covering to the framework. When, for example, damp silkspan has dried and shrunk, paint a thinned coat of dope through it to bond to structure everywhere the edge-bonding hadn't stuck things down.
The THINNER ONLY trick helps prevent CF veil fibers from pulling out of their matrix, btw. ANY dope, particularly Nitrate, is sticky and likely to pull CF fibers. Wicking-in the thinner creates enough bond that the next coat can be safely brushed on - with THINNED nitrate. After that, pulling fibers is unlikely, so go to it.
0.2 oz/sq ft CF unsized veil follows ridiculously varied shapes nicely, if you wick thinner through it for bonding, and prod it gently with a soft brush to turn corners, or fill gaps. Both silkspan and CF veil add enormous strength and hardness, at very little cost in weight with Nitrate dope. "Thumping" the surface with a fingernail shows that. Over simply doped wood, it sounds like a doctor thumping your chest or back. Over doped silkspan it has a harder sound, and over properly doped CF veil, it sounds like a hard plastic!
Why use dope for this? I heard somewhere that the lignin in wood (which is the bond between the wood fibers) is softened by a solvent like acetone, or the equivalents we use in dope nowadays. So the bond goes deeper than just a surface coating. It penetrates into the wood. Whatever the covering material, it BECOMES part of the wood. I hope I heard right about that - it seems to work out true.
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Hello Guys,
When it comes to the application with dope, Does it have to be nitrate or can it be butyrate?
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Steve,
It CAN be butyrate, but butyrate doesn't have the adhesive power of nitrate. A quart can of nitrate - which uses the same thinner as butyrate - can go a long way. The sticking power makes it worth using... Butyrates go over nitrate beautifully, once you have the essential bond that nitrate gives you.
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Steve,
It CAN be butyrate, but butyrate doesn't have the adhesive power of nitrate. A quart can of nitrate - which uses the same thinner as butyrate - can go a long way. The sticking power makes it worth using... Butyrates go over nitrate beautifully, once you have the essential bond that nitrate gives you.
So would it make sense to apply my covering with nitrate and then build up my substrate with butyrate?
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Okay, this is the result. I thined the nitrate dope to about 70% thinner and just blotted it over the carbon very lightly. After it dried I went back and did the edges. I found out that it's better to leave longer edges to wrap around so the little fuzzies don't stick up. As you can see, there is still a few areas that started to come apart but I think it's still an acceptable job. I'm not going to even think about touching it with sandpaper untill there's a few more coats of dope on it.
Thanks for the tips guys!
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Good start Clint!
And you're right - fill the fibers well with at least dope, or also - lightly- with a sanding sealer for final sanding.