abufletcher

I week ago, I would have made my decision about the covering based on ignorance or fear...or both. Now after the testing, I feel I can make a more reasoned choice.

If I choose anything other than the tissue+silk, I'm going to have to order materials from the US and that means that in all likelihood, the wings won't get covered until September (since I'll be in the US all through August). And I'm not completely sure I have enough silkspan either.

abufletcher

Hmm. I just checked and it appears that while I have enough silk and tissue to do the wings (both sides), I don't have enough to also do the tail feathers. Hmm. I could, of course, order more and do the tail feathers later, but I would want to dye all of the silk at the same time to get exactly the same color.

So it looks like no matter what method I end up choosing, I'm going to have to order materials (silk/koverall/solartex/coverite).

abufletcher

OK, I think I've gone as far as I'm going to go with the tissue+silk experiment. In many ways, it's a very satisfying method for simulating an old-fashioned fabric finish. In others ways, not so much. It offers an extremely tight finish...much more so than solartex. And it has the satisfying feel of old-time fabric. Solartex looks and feels like modern dacron-type aircraft fabrics. I'm more or less happy with the color (though it could be a tad browner) achieved with the coffee stain.

Final assessment through? Tissue+silk can produce a world-class finish, there's no doubt of that. But it's a LOT of work. A LOT! Also with all the layers and dope and paste and more dope needed to create that (semi-glossy) finish, it's probably a bit heavy for a 1/6 scale model. It would be better on a large 1/4 scale model. Also the work of doing the scalloped edges (twice) with this method didn't yield results that were significantly better than the shrunk solartex. It eliminated some problems but caused others. The silk itself is fairly easy to apply, but getting the tissue finish perfect first is critical. The silk won't hide any imperfections.

Then, there is the problem of the rib stitching. This would be simple enough if the wing were going to be painted. I'd just use torn solartex strips over real stitches. But since my wing won't be unpainted, the rib tapes all have to be the same color and cutting and laying down straight strips of the silk would be a nightmare (and it's probably too thin anyway). Again, if I could just do the solartex stitching then this hit it all with paint, it would be no problem.

But I've very glad I gave it a shot. I learned a lot and I may use this technique on some subsequent model.

pimmnz

Way back, when I was real young, an English modelling magazine, 'Aeromodeller', ran a series about designing, building and finishing free flight scale models. These were (mostly) WW1 models, and it was written by a chap named Eric Coates. Mid '70's, last century if I remember. The standard lightweight finishing method for these models was...tissue and silk. Was light because the lightweight Modelspan needed only water shrinking and a couple of thinned coats of dope to make it waterproof enough for the silk/wallpaper paste, which was well thinned with water so it was brushable. The silk shrunk as the water dried from the cellulose in the paste, and only a couple of thinned coats of dope was needed as prep for the paint. This series of articles is/was the basis for most of my designing methods, light, strong and designed to bend in a ding. If you run across any old Aeromodellers of the period...
I still don't know how anyone can get a 1/4 scale Fokker to weigh 20 lb, I have trouble getting them over 10...but I have the benefit of this old knowledge...
Evan, WB #12.

abufletcher

The weight is only one of the problems here. The two likely deal-breakers are the difficulties doing the scalloped edges with this two-step method and the problem finding a way to do the stitching without painting. The way I see it, if I have to paint to get the color, I might as well just use iron-on fabric covering.

What by the way, is the point of the paste? Why not just dope the silk directly onto the tissue?

abufletcher

This sounds pretty much like what I did. However, I used (medium) silkspan rather than the "Japanese tissue" commonly used on free-flight models. I gave the silkspan two coats of 50/50 dope, let that dry and then applied the very light Habotai silk with the wallpaper paste watered down to the consistence of a thick syrup, using a brush. However, this finish still seems to soak up the dope. I've already applied three more coats of brushed dope and the surface hasn't even begun to take on a shine.

At the moment the surface feels like 800-1000 grit sandpaper.

abufletcher

So it looks like I've made "no progress" since I started "building" again a couple of weeks ago. That's about par for the course for me. (PS. I don't really see it that way.)

abufletcher

And the winner is..................................KOVERALL! Shrinks like a champ, tight around the wire with the 1-piece wrap-around method. There's a LOT more shrinkage than with the solartex.

ulpilotrmh

My Feedback: (2)

Hey Don,

Now you've got it. Looking good!

Russ

Mein Duff

Thanks Don.. you just saved me many hours of testing with Koverall on one of my projects..until now I had only used Solartex but bought the Koverall kit recently...looking forward to the results and, if it doesn't have a tendency to over tighten and induce warpage Imay use it on my SE5 covering later this year...
Thank for doing us all a favor and and testing these various methods out..great reportage.

pimmnz

Ahh, the point of the paste...Seems that you are using far too much. The paste /water mix is used for two things, first, it works much better than dope to attach the silk, dope dries too fast and allows wrinkles to develop between the fabric and the tissue, and it seals the silk. You do not need more than a couple of coats of thinned dope to finish as the dope has nowhere to go. It is lighter than dope too, as most of the weight is water, which evaporates out.
As to the Koverall, or any of the light 'nylon, nylon chiffon' fabrics without an adhesive backing, it's all I use on 1/4 scale upwards, light enough and the weave allows the stuff to conform to most shapes, as you have found. I cheat, and use Balsaloc on the awkward bits so that I can iron it down to the tricky curves. Don't need to slit the edges, just pull it into place and iron it down. But whatever works for you.
Evan, WB #12.

abufletcher

Evan, do you use dope with your Koverall...or PU/PC to seal it? I used dope to stick the edges on my test, but I also have one small can of Stix-it (very hard to find nowadays). Frankly, I'd prefer not to have to use dope.

pimmnz

Yep, I use dope. Couple of sanded coats on the structure perimeter, then dope through the fabric with thinned stuff. Very old fashioned, smelly (lovely!), and messy, but it also provides the most durable and long lasting finish when combined with solarlac or water based paints, with plasticised two pot clear (gloss or flat, as required, by adding varying amounts of flattening) over top of everything. As for shrinking the fabric, just enough to remove wrinkles with the iron if using Koverall, and watershrinking with a touch of heat if needed with the nylon types. Enough coats of thinned shrinking dope to fill the weave, then paint. Thinned dope seems to need much less to fill than full strength, there will be a reason, but I don't remember what it was...to much dope fumes? Well, I've had plenty of practise and it works for me...
Evan, WB #12.

abufletcher

I don't mind the doping process (and didn't even get any dope headaches this time) but it's difficult stuff to get a hold of. It's simple enough to buy in the US but transporting by air (or even mailing) is technically VERBOTEN. And I still haven't found a seller in Japan, though there must be one. Model shops definitely don't carry it...even the internet ones.

So I have about 3/4 quart of non-tautening (Randolph's) nitrate and a quart of both non-tautening butyrate and tautening butyrate. Would you imagine that 3/4 quart of nitrate would be enough for all the coats on the wings and tail feathers? I would think so, but I'd have to run short.

As a final clearcoat I'll be using Nelson's Flat Clear (one part, water-based PU with a few drops of "catalyzer").

TFF

http://cooga-55.img.jugem.jp/20120114_47545.jpg
http://translate.google.com/translat...ed=0CFsQ7gEwAQ

Maybe you can ID the brand from the picture.

abufletcher

Thanks! I'll show that to one of my clubmates. It's curious that it's called "engine dope." I knew someone had to be selling dope because I've seen an article on doping silk in one of the Japanese RC magazines.

TFF

It said "Hot Fuel Proof" which was what Aerogloss dope has on its label. I bet they are referring to its fuel proofing capabilities in engine compartments.

abufletcher

I'm sure that's how most people think about it here. Japanese also talk about "engine urethane." I think there's one guy at the club who has a dope-finished model that he build almost 30 years ago as a teen. Basically no one builds...and the one or two guys who do build just use iron on films. I was able to read through the Japanese text on the link and it didn't give any further information. It was just a explanation of what dope is and how it's used.

Mein Duff

Ubrigens: "Stix-it" is still very available
http://www.sigmfg.com/cgi-bin/dpsmar...FV5.html?E+Sig

abufletcher

Stix-it definitely makes it a neater process. I found one of the 8oz cans on my last trip to the US and have just ordered another 8oz can along with my Koverall order. Technically though, because it's a flammable substance it's not allowed on airlines. By the way, does SIG ship internationally? I had my order shipped to a US address since it probably wouldn't have gotten here until the end of July and I'm leaving for the US at the beginning of August. Incidentally, I've found that in a pinch simple rubbing white glue onto the frame does basically the same job. The iron melts the white glue and bonds it to the fabric.

So looks like I need to turn to other building tasks for the remaining three weeks before my vacation. Certainly, there's plenty to do, but I had hoped to get the wings covered. Oh, well.

Mein Duff

Tried testing Koverall yesterday for my 1/4 scale rib stiching covering and found that the weave is much larger and more open than the Solartex I may use. The Koverall edges are easily frayed which is the effect I need, but the Koverall lower thread count per inch just doesn't look the part in general. This is the only fabric they produce.

abufletcher

To my eyes, the weave on the Koverall and Solartex look about the same. But, of course, since the solartex is already "sealed" it looks different from the undoped Koverall. Have a look at p.37 of Gwyn's Fury build for how he's doing frayed edges. Looks pretty neat.

http://www.rcscalebuilder.com/forum/...77&PN=1&TPN=37

abufletcher

It's worth noting, by the way, that the doped tissue and silk, while strong, is not at all puncture resistant. The sharp end of a bamboo skewer goes right into it (with an admittedly addictive POP) with very little force. In contrast, the same skewer with the same force doesn't pierce the Koverall. This might be partly because the tissue and silk actually forms a tauter surface than the Koverall, but ultimately the Koverall is just tougher stuff.

TFF

The koverall is tough stuff. Crashing a plane with the stuff requires no picking up of parts; makes a sack to carry the parts. Yes, you can poke a hole on the silk, but most dont have to make the plane tough enough to land on a bamboo forest.

abufletcher

My bamboo forests seem to be a lot more gentle than bamboo skewers. But seriously, all it would take is a ground loop onto a sturdy weed to poke a hole in the tissue+silk. Of course, some people have cushy, grass fields to land on.