I am building a rc-26 clipped wing cub. It recommends silk and doping . anyone have any tips or info on this method of covering?

I alway's cover mine with sig koverall and nitrate and butylrate very nice and tough stuff you will need very good venting though pretty smelling and flamable stuff or instead of butylrate you can use automotive paint too. if your still interested let me know and i'll fill you in a little more.

For a comprehensive discussion of silk techniques with lots of illustrations see Bob Munn's article in the October, 1993 issue of Model Aviation. You can order reprints from the AMA Library.

Dave Segal

Good reference, and actually, you can read it right online. Go to the AMA site, click on Members Only, put in your name and AMA number, and go to the archive. Everything is there in full color. Jim

thanks for the advice and links. I will look into it more. I have done alot of plastic but not this. Anybody have any input on plastic verses silk is welcome. Thanks again.

[I have done alot of plastic but not this. ]

What exactly do you mean by doing plastic??

sorry flap monocote

Without having read the article referred to earlier, here's how I've been doing it for about 45 years:

1. After the model is completed, give the entire framework (anywhere the covering will touch) 2 coats of clear butyrate dope (SIG, Aerogloss, or whatever - do NOT mix brands). Very lightly sand with very fine sandpaper, then give one more coat of clear and let it dry.

2. You can use silk, "silron" (blend of silk and nylon), "silray" (blend of silk and rayon), and I think there were a few others but can't remember what they were off the top of my head. Cut fabric so you have about 1" extra material all around the area to be covered. Lay the piece over the area to be covered and spray on a mist of water until the material is completely wet. (I used to use my Mom's Windex bottle filled with water many years ago, but any spray bottle will do). The material will cling to the surface you are covering. Smooth out any wrinkles or bubbles with your fingers, keeping the material wet, but not dripping.

3. While the material is still wet, take clear dope that is thinned 50-50 (clear butyrate dope and dope thinner) and brush through the wet fabric all around the outside of the area you are covering (whether it's "open framework" or a sheeted balsa surface). Immediately rub the dope in (through the fabric) with your fingers so it softens and bonds to the intial coats of clear dope under the fabric that were appled to the framework or sheeting (in the first step). Allow this to dry. You'll notice that as it dries, the covering, which was wet from the water you sprayed on, also dries and the fabric shrinks at the same time, giving a nice, smooth, tight surface. Once dry, trim off the excess material, and dope down the edges, again using your fingers to smooth down the doped edges. This is real messy and you'll notice how the dope dries on your fingers when smoothing down wet, doped surfaces - you can remove it with a bit of thinner on a rag (or you can "chew" it off your fingers for the next day or so! Did that for many years - maybe that's what's wrong with me - ingesting all that dried dope over the years!)

4. After all covering is applied to the whole model, then you start filling the weave of the fabric. For areas of open framework, using 50-50 dope/thinner, brush on VERY THIN coats over the entire surface, being careful not to push the dope through the weave. This would form puddles that will show when dry if too much goes through the weave. You just want to brush the dope on LIGHTLY at first. This is not critical when doping over sheeted balsa areas. As the weave fills, you can push harder (in successive coats) to continue filling until the fabric is completely filled (no more "pin holes" showing).

5. At this point, you will be ready to apply your color coats. This can be done by brushing (with colored dope thinned about 75-25 dope/thinner), or spraying, (again using about 50-50). Paint the lightest colors first, then tape off and paint the darker colors. I like to brush on my filler coats but spray all the colors. Then I shoot a coat of clear over the finished paint scheme to seal everything and to provide a final gloss coat.

Another product I've had good luck with is Dave Brown's "Skyloft" which is a very fine continous filament nylon. The procedure is slightly different in that you soak the pieces of Skyloft you're going to cover with in a pan of water for a few minutes. The difference is that while the silk (and silk blends) shrink while drying (after wetting them), the Skyloft expands when wet, then returns to it's original size when dry. Other than that, the procedure for covering is the same.

If you use straight rayon (or SIG Koverall), you must use Nitrate dope for doping the framework and attaching the fabric to the model. Then you can switch to the butyrate dope for filling and your color scheme. Once you start using the butyrate dope over the nitrate, don't go back to nitrate. You can use butyrate over nitrate but NOT nitrate over butyrate.

None of this is complicated. It just takes a few paragraphs to explain it - it's easier to do it than write the directions! It's a lot slower than ironing on plastic film covering, but it's much more durable and certainly more realistic. This method is exactly like real aircraft were covered for most of the last century, with the exception of using lighter and finer fabrics (like silk) for model planes. It's a perfect finish for your Cub project!

Does your building setup allow you to apply 8 or more coats of dope to silk without your spouse calling a lawyer about the stench?

Dave Segal

Nice post, linclogs (interesting handle you got there). I got some Dave Brown Skyloft and was disappointed to find it was heavier than Sig Koverall by almost 50%. I used some to patch up an old silk finish and it worked well except in one large patch where the dope has cracked on the surface. That has made me worry about using it on a whole plane. But your post makes me think about trying it anyway. It has a very nice look to it clear doped--similar to the old silkspan but even better.

Koverall has worked extremely well for me. Now I'm interested in trying Thai Silks. The Hatori 8mm comes in a terrific array of colors and the stuff is actually cheaper than Koverall. One post elsewhere said it weighs 1 oz/ft sq, which is heavier than the lighter silk from Sig. Koverall is 1.25, but doesn't need much dope to fill, so final weights are probably very similar.

I do almost all my doping outside, and even then I often use a mask. With a canister nose/mouth type from a place like Sears (under $20) I can't smell a thing. That also allows me to do some doping inside in the winter in a room that I can keep closed off.

Aerodyne nitrate adheres coverings very well, and it shrinks coverings pretty tight even without using water. Sig's Nitrate is treated to reduce shrinking, which also reduces adherence. Aerodyne, Sig and Brodak dopes are all totally compatible, except of course you can't mix nitrate and butrate. Pactra Aerogloss is a totally different animal.

I think a bad dope finish beats a good plastic finish, though certain styles look OK when the plastic is done really well. But plastic looks terrible when it wrinkles, lifts, or gets scratched, and patches always have ugly seams. I really like dope finishes.

Jim

looks like I will be trying coverall with stix it.all inputs welcome thanks again for all of the great tips.

I'd like to hear more about Skyloft from linclogs or anyone else using it. I did a google search and two people hated the stuff--said it took too many coats to fill, fuzzed when sanded, and sagged on humid days. But a couple people on RCU really liked it. I have some and I'm trying to decide whether to chance it on a plane. I'll try it on some scrap, but curious to hear what someone experienced with it thinks about the negative comments. Thanks in advance for any insight on this. Jim

Remember, just because the kit recommends silk and dope, doesn't mean you can't use an iron-on covering.

I would simlpy cover it the same way I cover all my other planes. Unless you're big on keeping up an old tradition, I wouldn't even think about an outdated process like that.

Re: Bob Munn's article - use your AMA number and go to the AMA website members only area to view past articles from Model Aviation.

buzzard bait--

Skyloft was heavier than Koverall? I've never weighed the two but find that hard to believe. Skyloft LOOKS sorta like tissue paper but I guess looks can be deceiving. I'll I have to check it out!

As far as using Skyloft, it is a little bit harder to use (especially sealing down the edges around rounded, curved areas like wingtips), and I think it does require a little more dope to fill the cloth. The main advantage to me is that it's similiar to working with silk but for a lot less cost. I think you can get like a 3-yard pack for a few bucks or so but silk that's packaged commercially by the square yard runs in the neighborhood of $15.00 or more!

I haven't tried any of the bulk places like Thai Silks. When I was in Thailand years ago, what they called "Thai silk" had little knots in the fabric - popular for scarves and clothes with the ladies but definitely not what you'd want to use for covering models. Maybe they've changed something or there are other types now, but I haven't checked because I've got a large supply of the different cloth model coverings on hand so am not looking for any.


Skyloft WILL fuzz when sanding IF you start sanding too soon. Wait until the cloth is filled and then only sand LIGHTLY - you can't sand it as hard as the other coverings.

I've had good luck with Skyloft and it seems even tougher than most of the other cloth coverings, but it does take a few more coats of dope than the other silk-like coverings

I think one mistake a lot of people make in covering with woven fabrics such as silk is thinking it goes on like tissue paper. Tissue paper takes far less coats of dope to fill. In spite of what I’m reading from other folks regarding using fabrics, I’ve been covering with "silk and dope" for over 40 years now and I’ve NEVER had any of those fabrics completely fill in "one or two coats" of dope. My experience is it usually takes at least 4 coats before there are no pin holes remaining.

MinnFlyer is right – you don’t HAVE to cover with fabric just because the plans call for it. All the old kits (before Monokote) said to cover with cloth (or tissue) because that’s all there was! But while some may consider it an outdated process, go to any airport and tell me how many real planes you find covered in heat-shrinkable plastic film? What I (and others) don’t like about the plastic coverings is they are not very scale-like in appearance. To us they have a plastic, "toy-like" look.

In all fairness, there are some iron-ons out there that are fabric and those look more appealing to me. (I recently bought an ARF Cub that has Goldberg "Ultracoat" covering and that looks pretty good.) But, having used the "old" silk and dope method as a kid, that’s what I learned to like and I just stuck with it. Also, I love the smell! (Wife hates it!) Maybe that’s what’s wrong with me. After all these years using dope – Dain Bramage!

So, yes, it takes more time. Maybe that's the appeal in today's "hurry-up world? Gotta have it now – can’t wait. Has anybody been checking out all the posts of older modelers lamenting about the proliference of ARF’s and there being less kits available?

And if I'm not an AMA member?

I like Supershrink coverrite.... unfortunately you can't get it anymore. I heard it was being discontinued a couple years ago and bought up all I could.... I have enough to finish my Waco then I guess it's back to Koverall.

Thanks, linclogs. I will give it a try.

I have a gram scale and weighed the whole sheet when I bought it--I was surprised too because Skyloft looks very light. The price is definitely right, but Koverall and Thai Silks won't set you back much either.

Another material I want to try is Polyspan, which is half the weight of Koverall and reportedly very tough. Problem is FAI Model Supply seems to be the only source, and by the time you pay postage it's $21 just to try out a sheet.

Several people have reported using silk from Thai Silks and have not reported any knots. What they sell actually comes from four different countries.

I completely agree about the plastic toy-like look of films. It really spoils the effect for me. Something magical about doped fabric or paper drum tight over a wood frame, and it gives the modeler a direct connection to full scale aviation. "Cub yellow" dope is the same stuff they used in Lockhaven, made by the same company, and it is still sold at local airports. Jim

Propfinger,

My .02 here and I've tried just about all the covering systems in 20+ years in the hobby.

A quality iron-on job will take about the same time as a good fabric job - some guys like Monokote, some like Ultracoat. Both are good. But after a while, the seams lift, they wrinkle and they are not as permanent as other types. If you're learning and expect to repair the plane a lot, it is the only way to go. Also for .40 sized planes and smaller, it makes sense as it usually comes out lighter than a painted finish, but not necessarily so.

Fabric and dope will give you a more permanent, fuel-proof, seamless finish. I don't like the iron-on, self-stick fabrics - they never seem to stay tight and the seams lift - they share the problems with iron-on plastic coverings. The colored ones (Worldtex, colortex, etc.) benefit from a clear coat of some kind of fuel-proof paint. The pre-painted ones were really heavy and didn't work well for me.

For years now I have settled on Sig Koverall glued in place with Sig's Stix-it or Coverite's product - glue you brush on the wood, then iron the fabric on and it sticks. You just need to glue the edges - where the seams go. Fabric that overlaps needs glue put in there too - the fabric doesn't have any. Shrink (carefully) with a heat gun. It will get nice and tight, and stay that way. Fill and seal with Sig nitrate dope, I brush it on. One other poster was right, I have never had two coats seal - more like 4 or 5, with a light 400 sanding between each coat. Some guys add a little talcum powder to help fill the last coats. Then I spray (you could brush) a coat of silver dope, then your colors. The silver evens things out, hides all woodgrain, and provides a good base for colors that have trouble covering - especially yellow. For darker colored dopes you can skip the silver step. This will give you an almost seamless, permanent covering. The downside is the cost and strong fumes that will run non-model builders out of the house!

I have just finished a project with a new system that is much lower cost, zero bad smell and water clean up - and the final result is 90% as good as dope. I use Koverall and brush-on glue like before, but fill and seal the fabric with Minwax water-based polyurethane finish from the home store. Two or three coats fill the weave. Finish with housepaint sprayed on with an airbrush, or you could use a foam brush. The paint works great, but needs to be thinned before using. Fuelproof final coat with a spray (gloss or flat) of Lusterkote clear - or any other fuelproof clear, as latex isn't. I use outdoor grade latex - zillions of colors are available and it's $8 a quart. Now, I don't know how many years this will hold up, but it looks great so far. (I've had doped planes for many years.)

Good luck, and if you have any questions email me.
Bob

Hi.....I've built 2 .40 size kits using monokote and am tired of having to constantly tighten and reseal the covering! I don't mind spending the extra time on a fabric finish, but I'm still unsure about whether Koverall will be OK for the type of planes I'm currently in to (GP Extra 300 .60, Bridi Sun Fli 5, King Kobra, and Liberty Sport -> mostly .40-.60 size stuff). Am I better off just sticking with Monokote? I'm not really concerned with getting a scale like fabric finish, I just want a covering that won't sag, bubble, loosen, or be a general PITA once done. Am I asking too much?

Thank you for all the great information posted so far!

Beau

Beaumiller, there is no question Koverall would work well for your larger projects in the sense that it is very strong--no worries there at all.

I do find that doping is something I enjoy on small planes but is tedious and cumbersome on larger ones unless I've got a really nice day to do it all outdoors, and even then it is a big job. It's part of the reason I tend to prefer smaller planes.

Two recommendations I've seen posted elsewhere that I haven't tried yet: use Weldbond thinned 20% with water and allowed to dry on the framework as an adhesive--then use an iron to adhere the Koverall. I just tried this on some Micafilm seams that were loose and it seemed to work very well. No fumes. I intend to try it on Skyloft next.

Use Minwax water-based polyurethane to fill the weave, and outdoor household latex for color, followed by fuel proof top coat like clear Lusterkote. I haven't tried this myself yet, but it would allow the use of foam brushes (which dissolve in dope) and I think it would go on easier and quicker than brushing on clear dope for the first coats. It also doesn't have fumes like dope, but I don't think polyurethane is safe to breath even if it is water based. Anyone know? Jim

Beaumiller -

I would go ahead and do the fabric and dope or water-based poly on the models you mentioned - especially the Liberty Sport and King Kobra. I think dope is a little lighter overall than polyurethane. Your real weight comes in with colored dope.

Use clear nitrate, with light sanding of 400 grit between coats, with maybe a little talc filler. You may look to trim some wieght from the airframe to compensate - older kits seem to usually be overbuilt anyhow. A good sanding job and fabric base preparation makes all the difference, and you'll use much less final color. Things start going downhill fast when you keep adding the colored dope or paint to even out a poorly prepared finish - that could be a killer on something like your Liberty Sport.

I did a Top Flight Contender .40 sport/pattern plane with Koverall and dope and it came out great weight-wise. Try the fabric and painted method - you'll never go back to shrink wrap again! (kidding - I use Monokote too - depends on the project.) By and large, for a large or a complex building project like a biplane, or any scale plane, fabric is the way to go for me.

One other thing I forgot to mention. Thin CA is great for getting the fabric to stick down in those hard-to-reach spots. Be careful with it as it can make a mess, but for wingtip edges, or wing saddles or hatch edges, a little thin CA rubbed in (keep moving so your finger doesn't get stuck!) bonds the fabric down forever. I also use it around wing-bolt holes or strut-attachment points for a durable job.

You can get away with a lighter structure with silk and dope as it adds a lot of stiffness to the structure. Becomes a stressed skin structure. twist a full size Cub wing with, and without the fabric on it and see the difference.

I think Sig Koverall is great stuff! I usually cover the sheet balsa areas like the fuselage, rudder and horizontal stab with silkspan and nitrate dope. Then use the Koverall on the open structures like the wings. This system is light and very strong.

I find that Koverall will seal with only a couple of coats of dope but it will only be SEALED not FILLED. In other words the weave will still show through if sealed and will be perfectly smooth if filled. Depends on the finish you desire and the amount of weight you can tolerate. I find that usually a sealed surface looks fine with a doped satin finish. A high gloss finish usually looks better with a filled surface.

I really like Koverall too, especially after trying Dave Brown Skyloft. Like 2fast, I found that Koverall seals in two coats, whereas the Skyloft requires endless daubing on the larger holes to get them to close up.

Someone mentioned putting on Koverall with slightly thinned Weldbond. I tried that with the Skyloft and it worked very well. I painted on the Weldbond with a foam brush, let it dry, and sanded lightly. Then I painted on a second coat. I put the covering on wet, and ironed it down to the dried Weldbond. On a test piece one coat was not enough to get it to stick securely, but with two coats it stuck so tight I couldn't pull it off. It added tremendous strength. Unfortunately the open frame parts were incredibly frustrating to seal. Koverall doesn't have that problem, and should go on just as well with Weldbond. Jim

thanks for the tips