After seeing Hammerd's outstanding Sopwith Pup from the Aerodrome RC kit and VonJ's very nice work, I'm thinking of giving Polyspan a try for at least some parts of my 1/6 scale DrI. It seems to be popular with the "small electric" crowd. What experience have you guys had this this or similar covering? Also how is it applied?

Here are a couple of links:

http://www.faimodelsupply.com/starline-polyspan3.htm

http://www.faimodelsupply.com/starline-polyspan2.HTM

i'm following this thread. thx.

david

Well Don, you already know how I feel about Polyspan from my e-mail, but for the sake of others, here goes. I love it! I was a die-hard Koverall or silkspan user. When I built the prototype for Aerodrome R/C's 57" Albatros C.III, K. Bengtson at Aerodrome persuaded me to give it a try. I was a bit hesitant trying a covering material I had never tried before on a model that I really wanted to turn out nice, but I went ahead and tried it. I was hooked from the very first minute. It goes on very easily. There is no adhesive on the covering itself. I used Sig Stix-it brushed on to the framework to ahere it, and then used a Coverite Trim Iron to attach the covering. I like using the trim iron because it gives me more control. I then used a heat gun to shrink the covering. It's worth noting that the C.III model has an undercambered airfoil. The model is 4 years old now, and the covering has shown absolutely no sign of lifting off from the undercamber. It has stayed drum tight, even under the hot summer sun. After shrinking, I apply 3 coats of nitrate dope, thinned with 25% thinner. After that, I use colour butyrate dope for finish, but any paint that sticks to nitrate dope would work fine.

Even on compound curves and wingtips I have never had a problem and wind up with wrinkle free covering. The secret here is to dig out the bigger covering iron, and then heat and stretch the covering as you pull it down around the curves. If you just try and mash the covering down into the wood, you will get wrinkles. Also be careful when shrinking. It is possible to over-shrink polyspan, and you will wind up with a hole where the covering has pulled itself apart. This only happens if you hold the heat gun in one place for way, way too long. If you shrink the Polyspan with an iron instead of a heat gun, you will avoid this problem entirely.
If you do get a hole, I have found that the best patch is a piece of silkspan. Tear a patch of silkspan the size you need (tearing will leave a softer edge than cutting, allowing it to be blended into the covering for an invisible patch), and spray it lightly with water and then dope it on. Sand the patch lightly, apply more dope, sand lightly, apply more dope, and sand lightly again. You now have an invisible patch.
Two areas you need to be careful with when using Polyspan.
a) Make sure you apply it so that the slightly shiny side is up! This is very important, because if you get the wrong side up, you will get a horrible case of the "Fuzzies" that will not go away, no matter how much dope you try and use.

b) DO NOT SAND HEAVILY BETWEEN COATS OF DOPE! At the absolute most, you may give the covering a very light once over with 600 grit after the 2nd coat of dope. If you sand into the polyester fibers, you will once again raise fuzzies that no further amount of sanding or doping will eliminate. Your only option is to strip off the covering, or lay on a piece of silkspan over top of the fuzzy area.

Polyspan is super strong, very puncture resistant, and holds its shrink. I have use it on my 57" Albatros C.III, 47" Fokker Dr.1, 50" Noorduyn Norseman, 41" Sopwith Snipe, and 78" Gotha G.IV. All 5 models look as good as the day they were covered. Not one has shown any sign of loose or sagging covering, and not one has a wrinkle. The finaltexture of Polyspan is hard to describe. It is not glass smooth like a plastic iron on, nor is it textured like a fabric. But it does have a slight texture to it that give the model a more realistic look (for a rag covered airplane, anyway).

I love it so much, I even made a video of how to apply it. When building the Snipe, I video taped myself covering the airplane, right up to the painting stage. Aerodrome R/C sells the DVD. I warn anybody thinking of buying it that it is hardly a professional production; just me, the Snipe, polyspan, dope, and occasionally my daughter's cat. But if you want to see how to apply it, I think (Hope!) it gets the point across.

Great description! I think I'm definitely going to have to buy a roll.

I'm curious though how polyspan compares to solartex. I'm assuming it's lighter (even with 2-3 coats of dope). I'm also assuming that it may be gentler on a delicate framework, but I'm just assuming.

Can anyone say whether Nelson's paints work well over nitrate? Or model acrylics? I like to be able to use standard acrylics for most exotic colors and then use the Nelson's flat clear-coat.

I don't have specific weights, but yes, I am 100% sure that a painted Polyspan finish will still be much lighter than Solartex.

The tail surfaces of my Gotha G.IV are built up from 1/8" X 1/4" balsa sticks, and the polyspan didn't warp it. It's still a good idea to try and shrink the covering as equally as possible, and also to try and dope both sides at the same time. The dope will taughten the polyspan a bit further, so you want to avoid unequal shrinking on delicate structures. On normal built up wings and fuselages, there's no problem with warping.

I've found an old can of SIG clear "Supercoat" butryate dope. What's actually the difference between nitrate and butryate dope? I know you're not supposed to put nitrate over butryate (because the butryate "gasses" longer and causes the outer nitrate layer to debond). But if you're only using one type of dope on a model, does it matter which you use? Also what's the advantage of putting butryate over nitrate?

Finally, what kind of thinner is used? Can I use just ordinary generic brand paint thinner or do I need a "matching brand?" Oh, yeah, and what kind of brush should I use? I'm assuming that a foam brush (my preferred painting tool) would just turn into goo with dope.

While I absolutely hate the dope headaches, the purist in me certainly likes the idea of using the same stuff as "the big boys!"

BTW, the thread below mentions sealing the polyspan with Minwax polycrylic. That would be way easier and I have lots of it. It's also mentioned that there is a "grain" in one direction. What's the best way to lay out the grain on, for example, the tail surfaces?

http://www.rcgroups.com/forums/showthread.php?t=170038

What's the best source for Polyspan? Can I order it directly from Aerodrome RC? Are the other suppliers with different size rolls?

Polyspan is best applied so that the grain runs parallel with the longest edge. So spanwise for wings and stabs. The only source for Polyspan that I know of is Aerodrome R/C, although there must be others somewhere.

As for the actual chemical differences between Nitrate and Butyrate dope, I have no idea. I know that Nitrate is not fuelproof, and butyrate is. Butyrate can be applied over nitrate, but nitrate can not be applied over butyrate. I have read that nitrate has more dope "Solids" in it, and therefore fills fabric and paper coverings faster than butyrate. Nitrate also makes a more compatible base for other types of paints. I have not experimented with using different brand thinners with dopes. I always use Sig Nitrate for the first coats, thinned with Sig brand dope thinner. Sig thinner can be used on both Sig Butyrate and Nitrate products. For colour coats, I use Brodak brand butyrate and Brodak thinner. I like the way Brodak dope handles. It also seems to have a higher pigment concentration than the Sig colour dopes, meaning I can thin it more and still get good coverage when I spray it. If you are experimenting with different brands, I highly recommend that you always do a test piece first.

Abu. Almost anything will stick to nitrate dope, but the only thing that you dare put over butyrate is butyrate. Be aware that there are two flavors of each; taughtening nitrate and non-taughtening nitrate; taughtening butyrate, and non taughtening butyrate. If you are using heat shrink, you probably would want to use non taughtening nitrate. At least that is what I am doing on my DVII.

On my Spandau's I used nitrate as a sealer and base coat, then Model Master paints over that.

A good quality automotive thinner will usually work, but test it first. The Home Depot stuff may work this time, and not the next, depending on the quality of the particular batch they got.

Les