dmcmike

My Feedback: (14)

No, not that kind of dope... I know there has to be some people on here who still use Silk and Buytyrate or Nitrate to cover airplanes. After many years of fighting with moneykote, and not having the kind of results i'm looking for, I'm going to go back and try silk again. I've already convinced myself (through some experimentation), that it's stronger, looks better, more durable, and with some care, is slightly lighter than plastic.

I'm looking for a source of silk, something other than the the little 3'X3' bag that's at the LHS. Anybody know of someplace online with appropriate materials?

thanks!
mcmike

da Rock

well...................

I'm glad you're interested in going back but......................

You're going to have limited sources for dope. Tower sells silk. Truth is, you can find silk in fabric stores that works great and is easier to get. Most every town has at least one fabric store. But as for the dope........

Do a Google for the dope. I know there is still one Control Line supplier that's selling it. I don't have his name right now. Look for the CL precision aerobatics guys (PAMPA) site. They're still using that stuff and I think they have a link.

As for a couple of the "attributes"....... Yeah, silk and silkspan both add good strength to balsa frameworks. However, they're not more durable at all. You can punch holes in silk or silkspan with no effort at all. The films are way better at resisting holes. However, films often won't provide good and constant compression/tension to a built up wing. When they get warm they don't pull as well.

If you've not tried UltraCote, you really ought to. It's lightyears better than most of the other films. It's got a "thread" matrix in it that gives it lots more ability to hold it's tension. It's also lots stronger because of it. And it goes on way better than most of the other films. I'm redoing a big 4Star today and wouldn't even be doing it at all if all I had to do it with was moneykote.

BTW.... if you want to improve the puncture resistance and the strength of open frameworks, try putting on TWO layers of silkspan. When you get the first covering to the point you'd start to fill and paint, lay the 2nd layer on. Don't sweat the areas where the paper covers compound curves that're over solid balsa and the job goes really fast. And you'd think the paint needed would be a TON, but the underlayer seems to cause the overlayer to take almost no paint to fill. If you run the grains of the two in different directions you get a bunch of strength from the covering. I've done a couple of CL precision aerobatic airplanes with the technique and it weighs about like a full blown silk job. And the silkspan finishes a bit easier than the silk. Takes less sealer and sands way easier.

dmcmike

My Feedback: (14)

I've found a pretty good source throught the C/L guys.. Brodak has butyrate dope, which is probably what I'll use. I've done quite a bit of silkspan and silk covering in the past (read '60's there...). I've tried ultracote before, but evidently, it has a grain to it, and shrinks better in one direction than another, because I've got a couple of spots on the structure where i'm constantly re-shrinking the covering. I'll probably use it again, sometime in the future... just want to give the silk and dope one more try, just for 'old-times' sake.

Dr1Driver

Doesn't Sig still sell dope?

Dr.1

LesUyeda

MCMike: Thai silk on line. 5mm at @2.5/yard. Aircraft spruce for clear dope by the quart (no hazmet fees), and Brodak for color.

Model aviation magazine has a great article by Robert Munn on "how to".

Les

dmcmike

My Feedback: (14)

Thai Silk!? that's what i'm looking for! I'll google it, but have you got a link?

I've noticed that spruce is getting a bit hard to find... I know midwest quit carrying 48" lengths of 1/4" spruce.

BTW, here's how I remember how to cover with silk...

1) sand the airframe
2) 1 coat clear dope
3) sand some more
4) another coat of clear
5) sand some more
6) cut the silk to size + 1"
7) put the silk in a tub of water, ring out excess water.
8) lay out the silk over the airframe, after squeezing the excess water out. Should be very damp, but not dripping.
9) brush some dope on the silk only over the framework, not open framed areas. use your fingers to make sure it penetrates through.
10)Let dry.
11) another coat of clear over all the silk, including open areas, either brushed or sprayed. let dry
12) another coat of clear (very light sanding to knock off any 'fuzz')
13) first coat of color
14)second coat of color
15) lay out trim with masking tape, spray edges of tape with base color (1 coat)
16) spray trim
17) spray final clear coat.

sound about right?

Jim Thomerson

Sounds good to me. I use a spray bottle of water and lay the silk down dry, then spray it. I like to keep it very wet while applying as it both sticks down wet better and can be moved around better. (sounds contradictory) Be patient and do it perfect. Keep the threads in the silk straight. Silk goes around curves very nicely. If you are using colored silk and want to do a transparent finish, make the first coat of dope very very thin. Otherwise there is a problem with runthroughs looking ugly. Keep doping until no dope penetrates the silk (go to thicker and thicker dope as you go along.) Dope the wood underneath well before you apply the silk, else the bays will be nice and shiny but the silk over the wood will still show grain. Use a new clean razor blade to trim. A dull blade or one with dope on it will snag and pull.

BWooster

You can buy dope at an aviation supply store. Randall still makes it, and if I recall, their website has the definitive dope finishing techniques.

I use silkspan and dope. I just looks a whole lot better. Plus, this is a hobby, and its fun to use an old fashioned technique.

The key to dope is to saturate the covering. Plus, you should apply all of the coats within a reasonably short timeframe. Dope is not paint, it is plastic. The plastic will be much stronger if it is all applied so that it binds to the previous coat.

Let me know if you want more info.

da Rock

A lot of guys use nitrate for the first coats because it works better. It gives better adhesion for the silk application. Somebody told me long ago that it was lighter, but truth is I liked it because it seemed to soak in better on the first coat and seemed to stiffen the wood better. And I couldn't figure out how much lighter it could be that would matter.

I've never sprayed the silk on the model because I was so apt to wind up with a dripping model. The silk laying against the wood gave the spray somewhere to go and would give all the water that hit the silk somewhere to go. The silk would simply pass water through to the model. What I'd do is, I'd lay the silk on a towel and spray it. The silk got perfectly damp that way. Any drops went into the towel and the silk came up uniformly damp. You want the silk damp and no more.

Jim Thomerson

In my shop, silk dries very rapidly, so I have to put it on pretty wet. I also think really wet silk is easier to handle than damp silk. I don't have nearly as much problem with sikspan. It seems to retain the water and dry much slower than silk. I think with any application of wet or damp covering the wood underneath needs to be well sealed with dope so that it does not soak up water. I very much like nitrate. I have had some problems with putting butyrate over nitrate. This does not seem to be a common problem, but I'd suggest checking for compatibility somewhere other than your model. Everyone says you should never put nitrate over butyrate.

LesUyeda

MCMike.

Sounds about right to me. I will usually dope the frame until I can see a slight gloss. Then I know it will not soak up any of the color coat.

Here is Thai Silks.

http://www.thaisilks.com/store/merch...tegory_Code=20

Nitrate dope sticks to just about everything, and you can put just about anything over it. Not true with butyrate dope. Also nitrate comes in taughtening and non-taughtening; butyrate also comes in taughtening and non-taughtening.

Whatever Sig is selling is not traditional butyrate, it is some formulation, and you must use there reducer. Their reducer eats everything that I have tried to mask with, so I threw all that I had away.

Les

dmcmike

My Feedback: (14)

thanks for the site, i'll be checking it out for sure. And thanks for the heads up on Sig's dope. Years ago, the last time I did anything with Silk, I used aerogloss. Not sure if it's even available anymore. Looking at Brodak's stuff, as well as Randolph. one last question... i always thought the difference between nitrate and butyrate was basically that nitrate wasn't fuel proof, and butyrate was, true story?

thanks!
mcmike

Jim Thomerson

Yes, I build a fair number of diesel powered airplanes. Nitrate , as well as butyrate, works well there. Aerogloss is incompatible with nitrate sometimes. I understand it is no longer made, and has changed formulations several times. I would use a non-tautening dope after the first coat to tighten things up, else my finishes have eventually cracked. Silk and dope do not like the sun very much, so cover your airplanes when not flying.

da Rock

I'm fairly certain that the CL guys have "relaxer" available for their dope. There is also a "retarder" available that is useful as well.

The relaxer is usually used in the later coats. It does what it sounds like. It keeps the later coats from shrinking as much. You don't use much at all, and I've never used it in the first coats. It's purpose is to stop the surface from going brittle on you. If the dope gets too hard it will crack and craze and the relaxer stops that. But too much of it isn't better than "enough". And some guys used to add a drop or two of castor oil to do the same thing, but there was no real info on that so it was hit or miss and often gave other problems.

The retarder is used by the guys who lived in humid areas and the guys painting in humid seasons. Dope dries faster than most paints and sometimes it'll dry so fast that it traps humidity. When it does, the humidity fogs the surface. You can wash the area with thinner, but it often won't look 100% and the thinner sometimes causes other problems. And some guys used to say that the retarder added makes the surface level better and shine more. I never knew if that was true, because most of them also shot on a bunch of clear overcoats and then rubbed out the finish. And I always did semi-scale and never cared for the polished glass look.

da Rock

And BTW, you really do want to use Nitrate to begin with. And it isn't fuelproof. But it's so much better to work into raw balsa, and nicely adhesive to new coats, and doesn't gum or puddle as much. But make sure to thin it some, even if you're brushing it on.

And also..... a lot of guys had no problems with blushing or cracking. So don't get the idea that dope is hard to use. It's not unless you live in a really humid area.... or a real cold one.

It's a shame that CL Precision Aerobatics isn't as popular as it used to be. There were a bunch of those guys who COULD PAINT AN AIRPLANE! A bunch of those models looked like poured glass. And were light as a feather. Dope, done right, is VERY light.

dmcmike

My Feedback: (14)

I've always admired the finish on CL stunters, and yes, they're light as can be. And the silk really adds a lot of strength to the structure, much more than monokote, so they can get away with much lighter structure.

What is used as a fuel-proofer over nitrate? I didn't think you could use butyrate over nitrate. Now what i'm wondering is, since this is going on a Gasser and not a glo fueled model, do I really need to worry about the fuel proof problem.

one more comment, why haven't the big IMAC 30 and 40%'s started using it. Just too much work?

I've made up my mind to re-learn how to use silk, and plan on doing my Giant Aeromaster with it as a 're-learning' experience.

LesUyeda

Butyrate goes over nitrate, but the reverse is not true. Being gas, you need not be concerned, except that colors are more readily available in butyrate. Brodak is made by Randolph, but Brodak claims a finer color particle size.

Les

dmcmike

My Feedback: (14)

That's what I was thinking for a gasser, it's a non-issue. Didn't know that Randolph made the Brodak product, good to know, makes the decision on what to buy a bit easier. I'm eyeballing the brodak candy apple colors with some curiousity...

SMUGator

This is a really timely thread for me. I'm getting ready to start a .25 size Ultimate Bipe from plans. I was thinking about using tissue and dope which I've done many times in the past and then paint with KlassKote to get an "old school" finish. I've never used silkspan, but I'm intrigued. How would you rate the relative difficulty of use and potential quality of painted finish using silkspan vs tissue?

Thanks in advance!

Tom

da Rock

Silkspan is really just heavier, thicker tissue.

I've only used tissue a couple of times but done a bunch of silkspan models. Silkspan will do some mildly convex areas ok, and is really very much like tissue for everything else, but doesn't have the stretchability of silk.

And of course, silkspan is what it is to hold multiple coats of dope, while tissue models often aren't doped at all.

Jim Thomerson

I do silk, silkspan, and tissue on a regular basis. Silkspan on a wing is really easy. Silk is just as easy but takes longer and more patience and care. Silk goes around curves very well, silkspan you have to cut gores to get it to lie down. I often silk a fuselage, silkspan wing, and tissue tail. Tissue you put on dry very carefully then water shrink it. Sig has a product called plyspan which is like medium silkspan. It has a little more body and is stiffer and harder to do a curved wingtip than old time silkspan. It is relatively tough and comes in colors. They also have litespan which is a slightly heavier tissue. Silk, silkspan, and tissue all have grain, and you want the grain running spanwise on wings and tails. There is some silkspan on the market which is like wrapping paper and not well liked. I wouldn't buy silkspan without looking at it first. It should show a fibrous structure and a definite grain. Silkspan tears nicely along the grain and torn edges are easier to hide than cut edges. Silkspan is what tea bags are made of if you want to see what a piece looks like. However, buying enough teabags to cover your airplane would be fairly expensive.

BWooster

Nitrate is used for first coats because it shrinks better than butyrate, and after it shrinks dry, it stops.

Butyrate does not dry as tight, and is not as stable once dry - it can shrink for a long time.

Retarder is also used for spraying, so that the dope has time to flow.

Rejuvenator is used to soften up an old coat, so that a new one will bind.

SMUGator

Ok, this probably falls into the category of "seriously dumb question". When you apply silk wet and use dope to fix it to the outside edges, how agressively does it shrink? Do you allow for shrinkage over open bays or stretch it as tight as possible on application?
My memory regarding tissue was to stretch it as tight as possible and only use shrinkage to get a taught finish.

Apologies for being a dumb (old) newbie.

Tom

LesUyeda

You pull it tought enough so that there are no wrinkles. As for how agressive is the shrink, these are the elevator halves for my Jungmeister. The black is 1/8 inch diameter carbon fiber tube. I used taughtening nitrate dope for the sealer/shrinker and it pulled the 1/8 tube out of straight by about 1/32 inch on each side.

Contrary to common belief, nitrate continues to shrink for weeks after dry enough to touch, and will eventually pull out any sag there is.

Jim Thomerson

From wet to dry, silk does not shrink a whole lot. So get it on looking to suit you while it is still wet. Silkspan shrinks more, I think, and will shrink a little more on rewetting. Even so, do as perfect a job initially as you can. One tip, let the wet silk or silkspan dry naturally. Don't get impatient and use your hair drier. It will shrink, and then go baggy. Dope is a thermoplastic and you can heat a wing to get a warp our or heat a small wrinkle out. I've dropped something on silk or silkspan and dented it, and with a hair drier pulled the dent out.

One other thing, when I have a wet wing ready to dry I see to it that both sides are equally wet, and I position it vertically, else the top will dry faster and you may get a warp. When doping, I dope both sides equally, back and forth, for the same reason.

One thing I do with an open structure, is to make small holes in the ribs, etc, and a small opening to the outside in an inconspicuous, oil-free place. So when sitting out in the sun and heating up, hot air is not sealed in and trying to stretch the covering.