Thread Tools
Oct 15, 2019, 02:09 PM
Registered User
Thread OP
Discussion

nitrate dope on balsa filler


Hello, I'm new to the RC hobby, I'm building the SIG Kadett MkII. I'm doing well with the construction, it's a lot like a wooden boat's construction. Right now I've got the wing built and most of the fuselage. I want to finish my plane as I recall watching older guys build them in the 50's- covering the wing with silk or fabric vs. plastic, and using dope. The hobby shops around here tell me everyone uses plastic now and nobody carries dope in CA but I have ordered some nitrate dope from Brodak and it's on the way.
On the wing I used a lot of the one-part "balsa filler" from the hobby shop. It's a dihedral wing and it came out pretty good except for some "uneveness" where the two wing halves meet on top, as well as other areas on the wing, where I used some filler to fair the surfaces. At this point I'm anticipating doing several coats of nitrate dope, sanding between coats, as well as filling uneven areas between coats with the balsa filler.
I am wondering - will it work painting the nitrate dope over the "balsa-filler" filled in areas? also, will the balsa filler work over the nitrate dope-painted areas. As I go thru the process of sanding, filling and painting to get a nice faired surface, will the nitrate be ok on the balsa filler and vice-versa?
I'm planning on clear butyrate dope once the wing is covered, but that's a bit off yet. Still don't know what to cover with but I hope to avoid having to use an iron or heat gun.
Thanks a whole lot for any advice! Bob
Sign up now
to remove ads between posts
Oct 15, 2019, 03:57 PM
Registered User
I have used nitrate dope over filler without any problems. I am not sure why you would be alternation between filler and dope. Thick build up of filler is not desirable. If you were making some kind of fillet, you should be using an epoxy product. There are areas like this on a Kadet.

I use nothing but dope and fabric on my airplanes. SIG Koverall is my preference. You should try to find a local modeler to work with you if this is the first time using these materials. I use nitrate dope throughout. I use butyrate colored dope for final finish. The clear butyrate shrinks more than nitrate and can cause warps. You can apply butyrate over nitrate, but not nitrate over butyrate. Nitrate is not fuel proof, butyrate is fuel proof.
Oct 15, 2019, 06:57 PM
Registered User
Some photos of the surface "unevenness" would be help.... can't tell if you have a problem relevant to soundness of construction/flight performance or are being obsessive about surface perfection.... a Kadet is not going to entered in a scale competition (smiley)

Michael in Ontario, Canada
Oct 15, 2019, 07:42 PM
Registered User
Thread OP

nitrate dope on balsa filler


Thanks for the replies. As to why I would alternate between filler and nitrate, and avoid using too thickness of filler:
well, haven't figured out how to add a photo yet, but basically the top surfaces of the wings where they meet at the center are a little off, so to maintain the juncture of the two surfaces in a straight line along the joint, I've added filler. At most, up to about an inch or two wide along one side of the centerline, maybe up to 1/8" thick in places. In my experience with boats (fiberglass over plywood) I use a two part fairing compound like bondo over the wood or epoxy.
So on this balsa airplane I was concerned that if I used a two part fairing compound it would be so hard that it would be difficult to fair (sand) it back down between applications without damaging the balsa surfaces around it. I figure the balsa filler will be much easier to fair. That's why I wonder how the nitrate will work on the filler. Also I'm hoping that adding coats of nitrate to the entire piece will impart a little hardness to the balsa wood so it's not so easily dented.
Of course things would be easier if I had a better fit between the wings! The joint is strong, used epoxy to join the halves and plywood gussets between them.
You used a word familiar to me - "fillets" - that would be the word to describe the material I've added to the wing juncture to try and get the proper angle and smoothness. Is there a better material than balsa filler that maybe I should be using in this application? Hopefully compatible with the balsa filler I've already started the fillet with? Thanks , Bob
Oct 15, 2019, 07:48 PM
Registered User
Quote:
Originally Posted by 2michaely
Some photos of the surface "unevenness" would be help.... can't tell if you have a problem relevant to soundness of construction/flight performance or are being obsessive about surface perfection.... a Kadet is not going to entered in a scale competition (smiley)

Michael in Ontario, Canada
I've seen some trainers built so badly you would wonder if they flew at all but.....they did. There's a lot of fudge factor in building a trainer, not that one shouldn't give it their best effort. However if it doesn't come out absolutely perfect the first time, is not to worry. Perfection takes time to accomplish.
There are some who build to perfection and the rest who build to fly. LOL! A trainer is not a subject for a display at Toledo although I've seen some free flight models there.
Oct 16, 2019, 05:38 AM
Registered User
Poly Fiber SuperFil is a great product. It sands easily, it can be feathered out using a finger wet with alcohol and is very light. Being a two part epoxy, it sticks very well to balsa and also aluminum. Fiberglass and nitrate dope stick to it well. The shelf life is good and remains use able for years.

https://www.aircraftspruce.com/catal...?clickkey=8866
Oct 16, 2019, 08:36 AM
Registered User
gene6029's Avatar
The Poly Fiber Super Fill is the cats meow. I use it a lot with dope finishes and never had any problems with it......Gene
Oct 16, 2019, 11:48 AM
Registered User
Thread OP

nitrate dope on balsa filler


Thanks guys I'm getting some of that! Bob
Oct 29, 2019, 01:31 PM
Registered User
Thread OP

covering nitrate doped wing


Howdy, thanks again for the tips, I guess even tho it's a trainer I'm doing this cause I enjoy the build but do hope to learn to fly it. I decided since it's available to use nitrate dope, silkspan and then butyrate dope. At this point I have built the wing and most of the balsa fuselage and have one coat of nitrate dope on both. I found that the nitrate dope went on okay over the balsa puttied areas. Next I want to cover the wing (probably with silkspan).
SIG's info suggests pinning down a piece over the doped & sanded wing - tightly with pins - then "painting" the wing with water , then going around the edges with nitrate dope. Don't say whether to wait until the silk is dry to go around the edges with dope, or whether if you let the water dry while pinned it will pull the silk off the pins, etc. I would think you would stretch the dry silk over the wing with pins, then paint the perimeter with nitrate dope, THEN wet the silk and let it dry, and then paint the entire wing with a couple coats of nitrate after the silk has stretched. How does this approach sound? Thanks, Bob
Oct 29, 2019, 02:21 PM
Registered User
Thread OP

nitrate dope on balsa filler


Well I just changed my plans after talking with Bob at SIG,, think I'll go with the Koverall vs. silkspan - didn't want to have to use an iron and just do it the old way but sounds like the Koverall /iron way will work better for me. Bob
Oct 29, 2019, 02:23 PM
Registered User
Thread OP

nitrate dope on balsa filler


Well, after talking with Bib at SIG I decided to go with Koverall instead of silkspan so I won't be using water. l was hoping to do this without an iron or heat gun but I think the coverall will work better. Bob
Oct 30, 2019, 05:40 AM
Registered User
Koverall is great stuff that is all I use. My method is to cover all solid surfaces with silk span and only use Koverall for things like wings. I thin the nitrate 50/50. SIG says three coats, I prefer 4 or 5. The wood should take on a slight gloss. When using silk span, you apply it wet. Spray it with water while the sheet is lying on a bath towel. Just make it damp with a water spray bottle. Lay it on the model surface and pull out all wrinkles until it is smooth. Apply the dope through the damp silk span to adhere it to the surface. Do not be alarmed with the surface turning white, this is blush and will go away with the next coat. Trim it around the edges after it is dry and word down the edges of the silk span; you want the edges to overlap.

Koverall. I start in the center of the wing. Apply a brush width of dope front to back and put the edge of the Koverall down into the dope. Pull it tight to get out the wrinkles. Push the Koverall down with your fingers into the wet dope. Smooth out the Koverall over the wing and work around the edge applying dope and sticking the fabric down into the dope. Do not be concerned about any small wrinkles; they will come out with an iron.

After the fabric is applied, dope the fabric lightly that hangs off the edge, after it is dry trim with a razor blade and dope the edges down. Continue to apply fabric to all surfaces before you heat shrink it.

Heats shrink it with a heat gun first evening top and bottom. Any wrinkles can be ironed d out over the solid areas. Then shrink the entire areas with an iron set at 300 degrees. Apply dope to the solid areas only and rub the first coat into the surface with your fingers.

To be continued. …..
Oct 30, 2019, 06:31 AM
Registered User
Continued.......

Koverall has some down sides, pin holes and adhesion. It is a man made fabric and it is difficult to get stuff to stuck to it. Nitrate dope works the best.

Pin holes over the soils areas is a bigger problem. You will not see them until you apply color finish. Then you will be upset. This is why I rub the first coat of dope over the solid areas with my finger. I want to push the dope into the weave. This is also why I use silkspan on solid surfaces like the tail and fuse, less chance of pin holes.

Adhesion, first use only nitrate dope. In the open areas of the wings I use this technique. I brush the dope only on the open bay with a brush. You want to wet the fabric but not to have it run through. I only do one bay, then rotate the wing over while I do a bay on the opposite side. Then rotate it back and rebrush the first bay area. This ensures the fabric is well wetted. Continue on for the entire wing. After the first coat is on, you can build up coats over the entire wing. I use about 6 total coats with light sanding between coats.
Oct 30, 2019, 08:42 AM
Registered User
continued.....

It is great you are building RC airplanes and not just taking them out of a box. Building and using traditional materials is a dying art. It is what I do, and I will never change.

Remember weight is you enemy. Do not get carried away to make it perfect. Just build it and fly it, enjoy. You will learn as you go along, every airplane will get better. I have been doing this for 60 years, I still am learning. I trying to make each airplane better.
Oct 30, 2019, 01:12 PM
Registered User
Thread OP

nitrate dope on balsa filler


Ray, thanks a lot for all that info. Of course now I have more questions! By the way, why do you go with Koverall only on the wing and silkspan on the solid parts like the fuselage?
So I'll have the wing faired and a few coats of nitrate dope on it, lightly sand it and lay on the dry Koverall over a fresh coat of dope on the center, laying it in with my fingers, then continue this process out the wing - since the dope dries so quickly I assume you paint it on as you go along - at this point I have a question - do you only dope it down on the wing's perimeter (center, leading and trailing edges, wingtip), or do you also apply dope and dope it down on the tops of the ribs, i.e. the cap strips?
Also, at what point do you apply the heat gun/iron to stretch it? Should the fabric be doped onto the ribs , or any dope on the fabric when you heat it?
Assuming you've heat shrinked the undoped Koverall, will the successive coatings of nitrate shrink it even more? Thanks, Bob


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Using Nitrate Dope on Polystyrene pardshaw Slope 18 Aug 11, 2017 10:04 AM
Question Nitrate Dope Over Acrylic Water Based Paint? kevin matthews Painting and Finishing Tips 5 Feb 10, 2017 11:18 PM
Discussion Polycrilic over nitrate dope? jgg12002 Painting and Finishing Tips 12 Feb 02, 2016 09:57 AM
Discussion can nitrate dope get used on wood filler? jeff262 The Builders Workshop 2 Sep 20, 2006 09:38 AM
Discussion what balsa filler can i use with dope? jeff262 Scale Kit/Scratch Built 6 Mar 15, 2005 12:02 AM