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-   -   Dope cover question (http://www.rcuniverse.com/forum/kit-building-121/11215573-dope-cover-question.html)

oldbassard 09-03-2012 06:26 AM

Dope cover question
 
Hey guys, I am 60 yrs old, been flying RC planes for 20 years or better and I have never used the dope covering. PATS CUSTOM MODELS has a Curtiss Jenny 60" short kit I'd like to build and use fabric or paper covering.

My question is, any recomendations of covering and the dope to use, brands types ect? Also what do you use to attach the covering to the wood? Can dope be sprayed on with an airbrush?

LargeScale88 09-03-2012 06:52 AM

RE: Dope cover question
 
Hi oldbassard,

The cloth and dope I've been using for years is all Sig products, which would be the koverall (availble in different sizes), Sig Nitrate Dope (used for sealing the cloth, and I also use it to hold the cloth down on the wood) and SuperCoat Dope which is used for fuel proofing, or adding some color.

The sig stuff has worked for me for years, but than some other people use different brands (can't think of any right now) and have success also. The dope I imagine can be sprayed on if you thin it out quite a bit, which would then take more coats to seal the cloth, but I've always brushed it on with good results. For application, I usually apply 2 coats of nitrate on the wood framework, sanding lightly between each coats. I than lay the cloth over where I just applied the dope, and I will now take some nitrate dope and seal the edges of the cloth, and the nitrate I am putting on now will soften up the coats I put on earlier, to make a nice bond. After that, I shrink the cloth so that the weave of the cloth will shrink freely across the whole area (for example over the ribs on a wing). After full shrinking is complete, I then apply nitrate over all the wing ribs to attatch the cloth down there, and after that, its just applying 2 or 3 coats of nitrate to seal the weave of the cloth.

Take a look at this thread here I did about a month ago, lots of good info on the application process

http://www.rcuniverse.com/forum/m_11181552/tm.htm

Its more work than iron on material, but IMO the results are much better, more rewarding, and the covering lasts ALOT longer.

Jason

soarrich 09-03-2012 06:57 AM

RE: Dope cover question
 
http://www.airfieldmodels.com/inform...wing/index.htm

Gray Beard 09-03-2012 09:44 AM

RE: Dope cover question
 
Silk is a great way to go with a Jenny. As a kid I used a lot of silk but even more silk span! With silk span you can shrink it after it is down just by using a spritz bottle with some water. Once dry you then cover it with coats of dope then paint. As in the How To article states, silk span is even more brittle? And can get holes poked into it with the greatest of ease!! Just for grins I would take a look at some planes covered in TEX covering? I'm not saying it is the way to go but it is another idea. The original Jenny was done in silk and dope though? {I think} or it could have been cloth. Another medium often used in both full scale and models.

buzzard bait 09-03-2012 10:07 AM

RE: Dope cover question
 
Polyspan is a great improvement on silkspan. It looks similar but is much stronger than silkspan and it is heat shrinkable. Lighter than Koverall. I like it a lot, and I like Koverall for large models. Silk is available from Dharma. Many threads on all of this.

Lone Star Charles 09-04-2012 09:05 AM

RE: Dope cover question
 
Speaking from my own personal experience: I have used Sig products in the past - their Koverall is a quality product, but their dopes have been a little difficult to come by from the LHS. Brodak has good quality dopes and reasonable availability. I have used Stits http://www.stits.com/products on my last two builds. I really like the Stits polyfiber fabric because it is available in very large dimensions and as a result, there seems to be less waste if you are careful when you cutout the covering pieces. Stits also carries every single thing that you need with which to cover whether you are building "scale" or just trying to "get it covered and in the air".Since they specialize in covering, they will have everything that you need to cover as well as thecustomer support.

Zor 09-04-2012 03:55 PM

RE: Dope cover question
 
I use polyester cloth bought at the fabric retailers for lining ladies skirts. About $5.00 a yard of length and 54 inches wide. Recently I bought some Ceconite light 1.7 oz per square yard.

My dope is Randolph purchase from suppiiers of full size airplane rebuilders. One coat of Randolph applied with a good qualiy brush is equivalent to three coats of Sig and of course three times less work and one third the cost.

Your choice.

Zor

carlgrover 09-06-2012 08:04 AM

RE: Dope cover question
 

Quote:

ORIGINAL: Zor

I use polyester cloth bought at the fabric retailers for lining ladies skirts. About $5.00 a yard of length and 54 inches wide. Recently I bought some Ceconite light 1.7 oz per square yard.

My dope is Randolph purchase from suppiiers of full size airplane rebuilders. One coat of Randolph applied with a good qualiy brush is equivalent to three coats of Sig and of course three times less work and one third the cost.

Your choice.

Zor

Exactly what I use. Uncertified light aircraft fabric and Randolph dope ala full scale. I think this is the cheapest way to go. Doesn't make a whole lot of difference in the price until you jump up from a .60 to giant scale.

Zor 09-06-2012 09:06 AM

RE: Dope cover question
 
Hi fellow modelers,

Some comments here to be evaluated or verified by the reader for his own benefit.

I have bought a supposedly pure 100% silk scarf to give as a Xmas present.
It was about 84 inches long by 18 inches wide. My cost was $98.00 .

It makes me think that Dharma's silk at their selling prices is not genuine silk made by the worms.
I am aware that many "labelled silk" products are some polyesters surface treated to feel and look like silk.

There is no need for that appearacnce of silk or the touch feeling once it is all embedded in aircraft dope.
Buying silk, genuine or imitation, is too expensive these days for model covering.

I still have in my hangar some models that were covered in silk and dope and are still wrinkle free and tight as a drum but they were built and finished in the late 1950s and early 1960s. One 72 inch wingspan model wings have no seam. A pair of silk stocking was pulled from tip to root and doped. That was my main model for home brewedradio controled experimentations.

I bought $152.00 worth of dope from the only nearby LHS and then discovered Leaven's Brothers, suppliers of material to full size airplane refinishers that sell Ceconite and Randoph dope.I bought from Leavens the same quantities of dope for $58.00 . I waited three months for delivery by the LHS as he was not carrying quarts. He only carried 4 oz small jars. Leavens had quarts in stock; I went there and came home with the dope and thinners.

I then found that three coats of Randoph was the same as nine coats of LHS product. Three time less cost and three times less work and three times less product out of the containers. You figure the advantages.

Your decisions ____

Zor

P.S.: I remember reading somewhere that Brodak brand is actually made by Randolph. I do not really have proof.

buzzard bait 09-06-2012 12:00 PM

RE: Dope cover question
 
Whatever Dharma and Thai Silks carry, it is WAY lighter than Koverall or Ceconite, and it is not expensive at all. If it's not silk, there's been some blatant fraud passing unnoticed for many years.

I've only tried Thai Silks, which was difficult because it is pre-shrunk; I mentioned Dharma because others said it shrank better.

Nevertheless, for smaller models when I'm counting grams, I will usually use Polyspan (NOT Skyloft, which is worthless).

I bought my last dope in quarts from Wick's; before that I bought quarts from Aerodyne,

Jim

soarrich 09-06-2012 02:12 PM

RE: Dope cover question
 
To test if it's silk do the burn test.
http://english.cri.cn/974/2005/08/18/63@10578.htm

Gray Beard 09-06-2012 02:15 PM

RE: Dope cover question
 

Quote:

ORIGINAL: Zor

I use polyester cloth bought at the fabric retailers for lining ladies skirts. About $5.00 a yard of length and 54 inches wide. Recently I bought some Ceconite light 1.7 oz per square yard.

My dope is Randolph purchase from suppiiers of full size airplane rebuilders. One coat of Randolph applied with a good qualiy brush is equivalent to three coats of Sig and of course three times less work and one third the cost.

Your choice.

Zor

Does this go on with dope then get shrunk using a spritz bottle like silk span?? Or is it like silk and doesn't shrink at all?? I have no plans to do any silk jobs any time soon but I have always wondered about the dress lining, if it shrunk tight or not?

buzzard bait 09-06-2012 03:52 PM

RE: Dope cover question
 
The burn test makes complete sense. I'll check out mine.

Zor 09-06-2012 09:06 PM

RE: Dope cover question
 

Quote:

ORIGINAL: Gray Beard


Quote:

ORIGINAL: Zor

I use polyester cloth bought at the fabric retailers for lining ladies skirts. About $5.00 a yard of length and 54 inches wide. Recently I bought some Ceconite light 1.7 oz per square yard.

My dope is Randolph purchase from suppiiers of full size airplane rebuilders. One coat of Randolph applied with a good qualiy brush is equivalent to three coats of Sig and of course three times less work and one third the cost.

Your choice.

Zor

Does this go on with dope then get shrunk using a spritz bottle like silk span?? Or is it like silk and doesn't shrink at all?? I have no plans to do any silk jobs any time soon but I have always wondered about the dress lining, if it shrunk tight or not?

[/quote]

Hello Gray Beard and others interested,

I can only write in terms of my experience.

In the late 1950s I built many light weight free flying models covered with silkspan and aircraft dope. As I remember the dope was branded Aerogloss. To me silkspan was a high quality paper and I did not know what it was made of. Some fellows claimed it contained some real silk filaments thus the name silkspan.

Later I started to build bigger models and silkspan was not suitable. It was too delicate and not very strong so I went to what I still think was real silk. I started using ladies stockings which were referred to as "silk stockings"; Like 50 denier and 45 denier silk.

Then silk stockings were replaced on the market by nylons. I used nylons stockings for a few models.
Then one day I decided that I needed more fabric strength and switched to woven fabric with a nap.

I remember covering a model with material from an old shirt not even knowing if it was cotton or whatever.
It did not matter because of a characteristic of aircraft dope.

Aircraft dope does not produce individual layers as more coats are applied. New coats fuse into the previous ones to form a single thicker layer. Another characteristic of dope is that it shrinks or I may say it tries to keep shrinking forever and thus keeps the covering tight for ever to my experience. Some models buil in the early 1960s are still tight as a drum and never wrinkled.

The fabric, whatever it is, is applied with slight tension to avoid wrinkles over a frame already sealed with a couple of coats of nitrate dope. the fabric is first glued on witht he dope all around the periphery and when cured the dope is applied all over. As the dope cures the fabric becomes tight. More coats creates more thension as the dope tries to shrink. No heat is used; the dope itself is shrinking and will contimue to do so for years and years.

I hope this covers your curiosity. Fabric and dope makes very strong covering to help the well glued structure.
You can land in a tree at flying speed without any damage. I have posted such a picture a long time ago and it was not a 10 oz model. It was an 11 lbs model with a fairly high wing loading.

Nuf said for now.

Zor




ARUP 09-07-2012 05:54 AM

RE: Dope cover question
 
Good info above. Here's a 1/2A Ringmaster covered with K&S '00' silkspan. The silkspan was attached to airframe with nitrate dope. It was then given two coats of nitrate and then lightly sanded before getting butyrate dope applied with a spray gun. The next pics are of an airframe covered with Koverall attached with Stix-It. The weave of fabric was sealed with nitrate dope then butyrate dope sprayed onto it. Any questions then feel free to PM. Cheers!

LesUyeda 09-07-2012 06:16 AM

RE: Dope cover question
 
"Or is it like silk and doesn't shrink at all??"

I have no idea where you got that information, but if I were you, I would check out my source of information. Silk DOES, shrink, and if applied fairly tight to begin with, the shrimk can be agressive enough to warp a light airframe.

Les

Zor 09-07-2012 06:19 AM

RE: Dope cover question
 
1 Attachment(s)

Quote:

ORIGINAL: ARUP

Good info above. Here's a 1/2A Ringmaster covered with K&S '00' silkspan. The silkspan was attached to airframe with nitrate dope. It was then given two coats of nitrate and then lightly sanded before getting butyrate dope applied with a spray gun. The next pics are of an airframe covered with Koverall attached with Stix-It. The weave of fabric was sealed with nitrate dope then butyrate dope sprayed onto it. Any questions then feel free to PM. Cheers!
Very nice ARUP.

Here is a Cessna 170 built in the early 1960s.

I do not remember if it was silkspan or so called Japaneese tissue.

It has radio rudder control using an escapement and a home made receiver and transmitter.

The wings are held on with elastics but we do not see them; the elastics are inside the cabin.

It is still hanging on the wall in my shack.

Zor

PatrickCurry 09-07-2012 08:41 AM

RE: Dope cover question
 
So if you go to Walmart and get something like the polyester or nylon dress liner, do you use the taughtening or non-taughtening dope?  Randolph has both the nitrate and the butyrate dope in the taughtening and the non-taughtening.  Randolph's page has dope to use on Ceconite which is 100% polyester and it says it's "non-taughtening" so does that mean if we use polyester from Walmart, we should use the non-taughtening and if so, how do we get it to shrink.  I'm so confused!  LOL

soarrich 09-07-2012 09:32 AM

RE: Dope cover question
 
You shrink polyester with a iron.

MTK 09-07-2012 10:28 AM

RE: Dope cover question
 
Quote:

ORIGINAL: LesUyeda

''Or is it like silk and doesn't shrink at all??''

I have no idea where you got that information, but if I were you, I would check out my source of information. Silk DOES, shrink, and if applied fairly tight to begin with, the shrimk can be agressive enough to warp a light airframe.

Les
Depends on whether you used "taughtening or non-taughtening" dope to apply. Taughtening dope will shrink down firmly and tend to warp an open structure. Non-taughtening dope really doesn't shrink appreciably. Randolph's dopes from Aircraft Spruce and Specialty have all the various grades outlined. Look on the AS&S website for the information on each dope type; butyrate and nitrates. When you are there don't forget the appropriate thinner for either butyrate or nitrate.

To the OP, a quart of nitrate (you use nitrate to apply coverings and butyrates to finish) is around 16$ and a gallon of thinner around 20$. If you model is electric and no glow fuel proofing is needed, no need to use anything but nitrate to finish. This is truly great material; it dries fast and fully flashes quickly withing a few days, and remains stable forever. But isn't glow fuel proof. Butyrate on the other hand takes many months to fully flash its solvent but is fuel resistant

Sig and Brodak are both thinned versions of Randolph's. The cost difference is at least 4X when you consider that Randolph's is mixed to a higher % solids straight out of the can.

BTW- I've used and recommend a spun polyester film from Model Research Labs. This stuff is super lightweight but really strong, is applied using common doping techniques and is heat shrinkable. You can apply it over open structures and closed just the same

Most importantly, the spun poly fills very quickly, quicker than any woven fabric so you pick up less weight from the paint as well. For a 60" model, weight has to be an important factor so keeping it as light and as strong as possible will give the best chance for success

buzzard bait 09-07-2012 10:36 AM

RE: Dope cover question
 
Shrinkage from dope and shrinkage of the material are separate issues. Dampened silk will shrink as it dries unless pre-shrunk.

My experience with Thai-Silks, which is pre-shrunk, is that even taughtening dope will barely shrink it enough. I put it on wet, doped around the edges, kept the surface damp while the edges dried. When the whole thing was dry I applied taughtening nitrate dope (Randolph from Wicks). The dope made it wrinkle, but as it dried it shrank. It took a full day or so to get it taught again. It was frustrating and I will not use Thai Silks again. Dharma is supposed to provide some shrinkage.

Jim

Zor 09-07-2012 05:33 PM

RE: Dope cover question
 

Quote:

ORIGINAL: PatrickCurry

So if you go to Walmart and get something like the polyester or nylon dress liner, do you use the taughtening or non-taughtening dope? Randolph has both the nitrate and the butyrate dope in the taughtening and the non-taughtening. Randolph's page has dope to use on Ceconite which is 100% polyester and it says it's "non-taughtening" so does that mean if we use polyester from Walmart, we should use the non-taughtening and if so, how do we get it to shrink. I'm so confused! LOL
I would not use polyester from Walmart.
I bought the skirt lining material from Fabricland.
I bought the Ceconite from Leavens Brothers.

Do not be confused. All aicraft dope does thighten in time.
So called non-tautening take a long time or tauten less.

Non tautening should be used for very light models with a weak structure.

There is no reference to tautening on the labels of the Randolph dope I am using.
I can assure you that it is tautening (thightening) within one hour and more so in 24 hours. Overnight you can tap it with your finger and it sound like a tambourine.

I have never tighten polyester with heat. The dope does a super job.

Simply said, we do our work our own way and gain experience over the years.

Zor

LesUyeda 09-08-2012 06:08 AM

RE: Dope cover question
 
" Dampened silk will shrink as it dries unless pre-shrunk. ''

I totally agree.

Les

Fleet 09-09-2012 08:52 AM

RE: Dope cover question
 
I get my Randophs supply from Aircraft Spruce.   UPS delivers and, sometimes, a hazardous fee is included.   Since I have a business acount with them, my CC is always good.

                                                                   http://www.aircraftspruce.com/menus/...hcoatings.html

I have found that buying in bulk for modeling is most wasteful.   After a some years , the dopes turn into a brown goo.   Now , I buy only what the job needs and not store up in bulk.   I will be testing the yellow I've had for some years unopened.  Cross my fingers.

The later non-tautening Nitrates come tinted and non-tinted.  Helpful to see where you been and , unless your painting light colors, not to much to worry about.  All require a 90 day or so gassing off so it smells likeaviation for a few months.

Around here in Coastal South Carolina, one must use some retarder for blemish control.   I sprayed the color on my 1/4 Fleet and used the Universal Retarder in lieu of thinner.   Still, a spot or two came up.  

This year, I'll paint my 1/3 Fleet in my friends EPA/DEHC certified paint booth.   Hard to call it a "booth" as he paints busses and UPS trucks in it.

                                          http://www.rcuniverse.com/forum/m_99...page_10/tm.htm  scroll to the bottom

As I age, I've found a good quality resperator is a must.   You'll be suprised at how some meds can react to the fumes.   Hells Bells, maybe that is why I am like I am.   chuckling.

Ray W.

Zor 09-09-2012 10:22 AM

RE: Dope cover question
 

Quote:

ORIGINAL: Fleet
>
>
>

The later non-tautening Nitrates come tinted and non-tinted.
>
>
>
Ray W.
We learn something new every day.

I have heard (read) that one company was tinting nitrate dope for use on smallmodel that would tolerate only a couple of coats of dope.

Nitrate dope normally comes only in clear dope to be covered with butyrate that is available in clear as well as tinted (colored).

Yellow and red butyrate should be applied over a previously white surface as these pigments are highly transparent. This avoid having to use many coats to obtain opaqueness.

Ask me how I know finishing my Spectra sailplane with wide yellow areas.

Zor




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