Mopzilla

Hi everybody! I am going to build a Dakota biplane - 30" span. It will be a 4-channel conversion with ailerons on both wings, on diesel fuel. Since this is an old airplane I'd like to have an old finish, yet put in a modern engine with modern electronics!

I'm also looking for the cheapest covering solution here. I was planning on getting Dave Brown Skyloft and then using three dope colors from Midwest. How is the covering done? Will it hold up to regular aerobatics?

Thanks!

Dsegal

Silk is not going to be cheap or easy to apply. But for a complete explanation of the process of covering with silk see the extensive article by R.H.Munn in the October, 1993 issue of Model Aviation.

Why not use Silkspan or Litespan on your model?

kdheath

Love the idea of the Dakota in silk. Last year I fulfilled a childhood ambition and built a FF Dakota to the original design. Cute!

Modeling silk (from Sig, for example) is expensive-up to something like 17 bucks a yard. A place called Thai Silks has nice silk for much less, but it is hard to get some that is as light as the model silk. You apply silk by clear doping the edges of the framework, laying the silk in position, damp, and brushing very thin dope around the edges to tack it down. The it is sealed with clear dope. Takes several coats. Finished silk and dope is very strong and torsionally stiffer than iron ons. Let me give you this link. It rambles a lot since it's a thread, but there are some good bits of info there.
http://www.aalmps.com/silk.htm

Midwest bought the Aerogloss line from Pactra and hasn't done a lot with it. Rumor has it that they are dropping it. It's been hard to find for a long time, many formula changes, etc. Short version-skip the Aerogloss and use SIG or better yet, Brodak dope. www.brodak.com Good stuff.

I'm not familiar with Skyloft, but it sounds like it might be a good option for the Dakota. Applied like silkspan or silk and stronger.
http://www.dbproducts.com/downloads/pdf/skyl_header.pdf

How about a picture of the Dakota? Is yours from the magazine plan that was published a few years ago?

Mopzilla

Thanks for the help! I apologize for not being specific - I meant a synthetic replacement for silk - silkspan, litespan, skyloft, etc. Skyloft is less than $5 for three square yards.

kdheath - I have not started building yet, but the plans are coming soon. I have never seen that article. I got in touch with Joe Wagner and he recommended that I build a 125% Dakota when I mentioned an R/C conversion, so when ordering he offered to enlarge the plans for me. I should have them by the end of next week. I just wanted to make sure I'm getting the right stuff from Tower, so that the plans AND parts can come in the same time!

Here is somebody's dakota... however, it's a FF one I think. Mine will be slightly bigger, with four ailerons and a full 4-ch setup.. still debating between two aileron servos or one. I am planning to make the wings removable and the insides easily accessible. Here's one cutie:

LesUyeda

I have used Skyloft, and keep returning to silk. I found Skyloft much too agressive in the shrink for light airframes. Thai 5 mm silk is esentially the same as K&S aircraft silk, and is $2.50 per yard.

Les

Gollywock

A lot of people (including me), have had great results with Polyspan. Looks like silkspan, but shrinks with heat. Available from BMJR http://www.bmjrmodels.com/ Jim

kdheath

So Skyloft is water shrunk? That's interesting for what the instructions say is a nylon material.Would Sig Lite-Coat dope help with controlling the shrink?

Yep, I've seen that photo before. That is good one.

I knew that someone had done this before. The article was in Model Aviation. The article also mentions that Clarence Haught started the ball rolling with a 25% enlatgement, and this one is even bigger. Article might helpful on yours:

Issue: November, 1981 (AMA8111)
Title: Dakota Grande Pages(7)
Author: R. Wrisley

balsaworks

One technique that you might consider if you want to use silk, is to double cover, either with silk over mylar or silk over tissue.

Silk over tissue is used by some of the top guys in FAI RC scale. World class F4C competitor Pete McDermott uses it on all his WW2 models, but the technique is even more useful for sport models. There are several advantages:

It´s much easier to handle & apply the silk when you have a backing already applied.
It´s A LOT easier to apply dope, when the dope can´t run through the weave and collect in drops underneath.
The covering gets stronger and yet lighter since you need only a fraction of the dope required to fill the silk alone.

I use Silk over tissue on all my gas powered models from ½A & up. Cover with the tissue first. I use Esaki & nitrate dope. Put on enough coats of dope to fill the pores of the tissue and let dry thoroughly.
Then lay the dry silk on top of the doped tissue and brush wall paper paste right through the silk onto the tissue. The wall paper paste leaves very little residue as it dries and adds very little weight. It should be a fairly thin slurry that brushes on easily.
When dry, the covering is air-tight and only needs a couple of coats of dope. This will leave a very attractive finish with preserved weave structure, unless you add many more coats of dope to fill the weave, which isn’t necessary.
Again, the end result is lighter than silk alone which needs lots of dope to fill the weave & make it airtight.

The (modified) Twin Lizzie in the photo below is covered with this technique, the paint job is airbrushed coloured dope. It has a wing span of 30�, 2-ch Cannon micro radio and a British DC Dart .036 cu.in. diesel. A.U.W. is 11 oz. The finish has lasted for 15 years.

Jim Thomerson

I've done just the reverse, putting tissue over silk. Just a little dope on the silk, put the tissue on, water shrink it and then stick it to the silk with thinner. Now that I think about I may have put the tissue on dry. Anyway, It came out nice. I want to try the tissue over mylar trick sometime. Sounds like it gives a very strong, light, rigid structure. Silk over tissue as you say is good for looking like fabric (because it is).

Lou Melancon

Can silk be put over doculam? I have an Early RC Live Wire Champ just about ready for finishing and plan to use colored SIG Silk. I have seen paper over doculam mylar but not silk. I am guessing it will work.

A couple of questions for those of you in the know:

1. Should the bare balsa be doped and sealed before applying doculam?
2. Should the doculam be doped once or twice before applying silk to it.
3. Is thinned nitrate dope the preferred method for sticking the silk to the doculam

Thank you for any assistance you can provide.

buzzard bait

I tried Skyloft on a BUSA Stingray 40 and I am now a FIRM Skyloft opponent. You'll never buy so much aggravation so cheaply.

You put it on wet and there is no control over shrinkage, and it shrinks A LOT! It warped part of a 40 size airplane. It is also the heaviest unfinished covering material on the market that I have ever found, and I've checked out most--it is heavier than Sig Koverall, which is a far superior product (though it is overkill on such a small plane). Skyloft is extremely difficult to seal because the hole sizes are uneven and some are quite large, so it takes a lot of dope. No one should sell stuff that bad.

Polyspan is a very good synthetic that looks like silkspan, and it is much lighter than Koverall, yet very strong. It can be heat stretched around curves if you paint an adhesive on the frame first. I used Weldbond. It seals in 3-4 coats of dope. Don't sand until sealed and then only lightly with extra fine grit or it will fuzz up.

Airspan or Litespan (Coverlite) are even lighter--synthetic tissues, really. A little more difficult to work with because of very limited shrink, but I have seen beautiful results. I've used it on tail surfaces to keep weight down. Neither this nor Polyspan wrinkle later on the way plastic films do. Koverall and silk don't either.

Thai Silks is one I haven't tried yet, but a friend has and liked it. It doesn't shrink very much and must be applied wet to get some shrinkage. It is heavier than the stuff Sig sells, but takes much less dope to seal, so the final result is still acceptably light for a small model. If you use Brodak nitrate for the first coats it should shrink some more (Sig Nitrate is treated so it doesn't shrink). Nitrate is diesel fuel proof. If you want color you can paint color butyrate over the nitrate, or get colored nitrate from Aerodyne. Aerodyne also has clear nitrate that shrinks. If they are still in business.

Good luck,
Jim

Stickbuilder

Skyloft as well as Koverall and other synthetic wovens are very predictable in terms of Thermal shrinkage. If you can control the temperature of your iron to a cooler temperature, you will not over shrink the fabric in either the warp or weave direction (read that Machine direction or Cross direction) If you are cautious with the heat, you can utilize this type of covering on the lightest of structures without fear of crushing the framework. Conversely, if you are of the too much is just right school, then all bets are off.

I have used synthetic wovens for years with no over shrinking, and best of all, it is inexpensive, and holds up extremely well. I wish you would try it (first build a dummy structure, and use it to test your skills). You will find where the fabric begins to, "Move" and stop there with the thermostat. You may even want to back up a notch, since you probably did not give your iron time to level out.

Bill

eurekahobby

My Feedback: (37)

I learned a trick from Japanese modelers who couldn't get or afford dope. They doped their models with gelatin. It is light weight-beautiful and can be overcoated with dope to make it water proof. Their planes were great as long as it didn't rain or mist at a contest.

Jerry Asner
Eureka Hobbies Inc.

buzzard bait

Stickbuilder--Skyloft is not woven and not heat shrinkable--see posts above. It's like the stuff on the bottoms of chairs and couches. It probably IS the same--that's why it's so cheap. Jim

Stickbuilder

What was the name of the other woven...It bites to be getting old. It was sky something. Woven and similar to Koverall, haven't seen any in a long time. At any rate, I'm using Koverall on my WACO (old PICA kit in 1/5th scale) In fact, I had to get my LHS to order the Koverall and Nitrate dope. What is this world coming to?