blu4ski

*****

Back in the 1980's I built an ultra-light single place aircraft called a "Koala". It was wood construction, pine and aircraft spruce. The wood was primed before cover with urethene varnish. Also the first sealer coat on the poly cloth cover was varnish, followed by a two part epoxy auto paint finish.

My question is: Have any of you brave souls ever tried using varnish or a Krylon clear coat or Whatever ???? I would think there should be some thing else usuable beside dope on our model aircraft.

What say you .....

cyclops2

I now use thinned down color paints on a VERY stretchy Polyester Mosquito netting.
I have used a womans Nylon stocking & paint.
Gives a very smooth surface. WEAK, but smooth.

Rich

ffkiwi

I think it largely depends on whether you require the covering to shrink under the action of whatever coating you apply. If yes then dope is probably still the only option. If you can shrink the covering by heat, or apply it tautly enough in the covering process that subsequent shrinkage is unnecessary then other options come into play. If you're using tissue, silk or nylon as a covering material then you're pretty much stuck with dope for the initial stages-though final finishing coats might be any number of similar or dissimilar products as long as they were compatible with the underlying coats. I've used dopes, non shrinking dope, coloured dopes, enamels, two part mixes, acrylics etc over the years in various applications, brushed and or sprayed.
Some folk swear by krylon and others by floral colour sprays. I've seen people use lightweight glass (on sheeted surfaces obviously!) attached with water soluble polyurethane varnish.

'ffkiwi'

Tom Nied

I've heard guys use certain Krylon colors and even some of the Walmart spray paints. Problem you have with 1/2 A's is the high nitro content. Where you can get away with those paints and 10%, you might get colored mush with higher nitro contents like 20%. Certainly a good test or some research might reveal some interesting results. The guys I have known who used the Walmart paint really would do a good drying period like at least a week. Even sometimes putting it in the car during Summer to really get it to cured solid. I remember even Butyrate Dope doesn't do all that great with higher nitro contents. But it is light.

BMatthews

For electric power there's lots of options as long as it supplies the shrink and taughtness we need for a good covering. But for glow powered not so many. The fuel proofing is the issue as noted above. The only thing I've ever found to be fuel proof for 1/2A fuels is Flecto Varathane. The original formula that is not the water emulsion does a pretty good job against up to mid teens nitro. The water emulsion stuff may work but I haven't tried it. If you go to try some of the emulsion varnishes watch out for Minwax Polycrylic. It's not fuel proof in the slightest. Turns into a gooey mess at the first sign of any model fuel.

I tried Krylon way back in my youth. It made the jap tissue on the rubber model both saggy and crispy all at the same time. Had to redo it. Others have had decent results with Krylon but I gather it still doesn't make the tissue taught. Also it isn't fuel proof.

The spark gassies get away with almost everything. But again a lot of enamels and latexes do not supply the taughtness we desire in the open covering.

blu4ski

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These are some GREAT replies. Thanks and keep 'em coming.

skaliwag

My Feedback: (1)

Just read the story of "Colditz", the castle where the Germans kept das Deutchfeindlich. They built a glider in the attic and covered the wings with cotton sleeping bags, shrunk the fabric with Millet, ground super fine and boiled for 4 hours. This was applied hot to the skin and when cooled and dry, it produced a smooth, glossy surface which had shrunk the fabric so that it became as taught as a drum.

MJD

My Feedback: (1)

If you are talking glow power the very real problem is that fuel is a really good solvent, especially the nitromethane part that small engines love. Nitromethane dissolves cured CA for example. So while there are lots of ways to make pretty finish, your choices are drastically reduced when fuel-proofness is important.

Even butryrate dope is only moderately fuel proof and will succumb with exposure to higher nitromethane contents. As noted those other finishes seem resistant to up to about 15% nitromethane - which is also the same rating given to TopFlite Lustrekote "fuelproof" paint - so the fuel proofness is not rock solid, but it works for most sport aircraft. Many two part auto finishes dissolve happily when exposed to nitromethane as well. If you want serious fuel resistance you need an epoxy exterior coat or a plastic film with the edges sealed.

Well that helped not at all, I was just babbling again..

MJD

Tom Nied

Actually that "babbling" could have saved me from making the mistake of a fuel splatter when transferring fuel from one bottle to another in the garage, where my new motorcycle sits. But also the epoxy suggestion was what I was thinking also. I always put a thin coat of epoxy around the motor mount/tank area. I think another thing that helps is wiping up any spills or drips as soon as possible.

MJD

My Feedback: (1)

Oh dear - it's nearly as fearsome as brake fluid depending on the paint chemistry. And on a bike too.. I mean, a car is one thing. But your bike? [:@]

For sure, when the fuel sits there it is acting like low viscosity paint stripper. Same deal on our airplanes too unfortunately, though with exhaust the amounts of active solvent are greatly reduced. But there is always some residual nonetheless as combustion is not a perfect process. So in other words one good piece of advice is never to count on combustion to rid fuel of its solvent habits.

The phrase "hot fuel proof" is subjective - it depends on what % nitromethane content you call "hot" fuel. It probably is subject to to what you define as "proof" as well, . i.e. can you line a tank with it and leave it filled for the season, or is it resistant enough that temporary spills don't trash the finish the first few times? If you see what I mean.

In the end, my advice is to never be surprised by what model fuel is capable of attacking, dissolving, and rendering unrepairable - that way you are always finicky about finishing and stand a fighting chance. If we could only paint our model to our satisfaction, then feed it into the magic 1 mil fluoropolymer film coating machine.. or something like that. With color graphics too.

MJD

MJD

My Feedback: (1)

I remember that indeed, but from the tellie quite a long time ago. Was it a feature film, or the '70's series where I saw this? I recall the prisoners getting extra helpings of oatmeal to get the starch, and rigging an iron bathtub as the drop weight, the lame part when the wing strut on the model failed as it thermalled up, temporarily dashing their hopes and all that. Better it went into a spiral dive or fluttered off the rudder, but hey, snapping the strut is certainly a possible and maybe probable full scale possibility with a glider made of bedframes and whatnot. I recall a line something like "..Major, you and I are in a lot of trouble.." as the glider headed off into the sunset, or at least the valley.

MJD

skaliwag

My Feedback: (1)

In reality it never flew.. It was finished but the castle was liberated before opportunity arose.

MJD

My Feedback: (1)

I'm thinking of "The Birdmen" it turns out.

"Major, I'm afraid we are both in a great deal of trouble."

blu4ski

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As the originator of this thread I wish to add that hot fuels are not an issue. I'm nearly ready to cover a Ben Buckle Buccaneer free flight that may never see an engine. At my age I have not the spirit to be chasing after a wayward thermal sniffer.

I have not decided on what cover to use. I want to use a colored cover with a clear coating.

By the way, I experienced three engine out landing with the Koala ( looks like a 3/4 size piper cub )back in the early 1980's. Two ended up on the local airport and one in a remote hay field some distance away. That leaves one with sweaty arm pits.

ffkiwi

The only really really fuel proof paint I found (here in New Zealand) was a two-part polyurethane mix called 'Reaction Lacquer' produced by Epiglass for the (full size) yacht market. I have fuselages painted with this stuff that are still good nearly 30 years later-after having run as high as 45% nitro. [models built 1981-82] The downside is that it was (i) damned expensive (ii) limited range of colours (iii) contained lead (iv) heavy (v) the hardener would set in the can as soon as look at you and (vi) stunk to high heaven when being applied.......but aside from all of these...........

Actually, I imagine it could be sprayed, in which case a much lighter finish would be possible-but you would need full breathing gear-the stuff contains isocyanates (remember Bhopal, in India? The Union Carbide plant disaster?) Whether it has any advantages over say, K&B epoxy paint, is hard to say.

For general fuel proofing, I use another Epiglass product-'Everdure' -a marine wood preservative-that comes as a two part epoxy mix that is very thin, brushes well-and is compatible with dope-so you can patch over the top of it, without problems. Works on all the non plastic covering that I use (tissue/silk/nylon/Polyspan/Coverall/Skyloft). Epiglass seems to be now a product line of International Paints-in turn a division of Akzo Nobel-see www.yachtpaints.com

'ffkiwi'