Pre-Covering Dope on Wings?

What is the consensus or advice regarding whether to dope the entire wing structure prior to covering. I have never done this but havent had any planes last long enough to care. I suspect it might be better regarding humidity changes, warps, etc.

Thanks

LAST EDITED ON May-22-01 AT 09:27 AM (EST)

That is two good reasons. Others are it strengthens the structure, helps to oil proof it (plane lasts longer), no worries about warping when applying the wet covering, better adhesion of the covering, and much easier to apply it.
I always dope everything in the wing, not just the perimeter (the fuselage too), at least enough to get a good sheen on all the parts.
Full-size aircraft practice on wooden airframes requires ALL surfaces (including the insides of box spars and the fuselage interior, everything in other words) to be protected, and it is done for good reason. It is more work, but well worth the extra effort in the long run, if you want to keep your model around a long time.
There was an article in MAN in about 1963 or 64, that a gentleman wrote on the subject of making models last (it may have been featured in "Round and Round", although I seem to recall it was a separate article on it's own. One example he used was his old Veco Brave, which at the time was 14 years old, had gone through six engines, and was still flying and looked good (glued together with Ambroid too). This was one of the things he did, and it impressed me greatly.

And when you're covering sheeting, like on a wing leading edge, pre-doping will keep the balsa grain from rising when you get water on it while silkspanning.

I notice that Windy dopes the entire framework, and some of his stunters are 15 years and older and still flying well. I have started to pay more attention to longevity as the effort and money I put into the birds has increased. Just a coat or two of majorly reduced dope.

Don't claim to know as much as others, but I now coat the inside and outside of every structure with nitrate, sanding sealer, and another coat of nitrate/or butyrate for fuel-sealing purposes. No, I don't sand the sealer inside the fuselage box or wing center section, as that would be darn-near impossible without destroying what I made, but in my (very) limited history with these ships, fuel soak inside the structure is very damaging, long term. Anyway, I may add one ounce weight, but peace of mind is worth it to me.
These are fairly thin coats, but just enough I don't worry too much about fuel. I will sometimes brush a thick coat inside the fuselage over glue joints, though.

I have always predoped the entire structure, especially on my free flight planes. A 50/50 dope-thinner mixture so the dope will soak into the wood. Second coat I use full strength and then when the damp tissue, Japanese or silkspan, goes on the wood, I use straight thinner to tack it in place followed by the 50/50 dope. I use a water/alcohol mixture to shrink the tissue and then dope it. I always use the 50/50 here too. Three coats, lightly sanded between each coat, then your favorite finishing method. Some folks use Nitrate dope on the first coats to get the cover tight, but not so tight it warps things, followed by Butyrate dope. Never put Nitrate on top of Butyrate. It jus don work mate. I hope that helps some. Ty M.

Here is an option: Use polyspan on built up wing pannels, you can then use just plain old nitrate for all substrate work. You don't have to wory about using butyrate dope to shrink the tissue. It just takes a heat gun to shrink the polyspan. Here is the method I will probably use on the next model I build: Polyspan on open bays. Cover the rest of the model with medium silkspan put on with nitrate. 4 coats of nitrate sanded lightly between coats; 1 or possibly 2 light coats of automotive touch up primer/sealer acrylic laquer, (wet)sanded well. 1 very light coat of auto touch up primer. Spray on colors from auto touch up acrylic laquer spray cans. Do ink work and letterings ect. Then two light coats of polyurethane clear coat. This should be fuel proof enough and reasonably light too. My reason for using this method is that it can be accomplished while living in an apartment complex and you don't annoy your neighbors with excessive overspray and compressor noises.

Curt --

Ugliness and difficulty with covering is a direct result of not doping / sanding sealing the basic structure to high standards. Forget about internal fuel proofing. Get the darned thing finished, then cover the finish. Those pretty ribs just that are already finished support the covering in a way that raw balsa ribs cannot. Raw balsa gets all swollen up when water gets around, and forms lumps and I don't know what all.

One of my old flying buddies was a nut on this, and his planes looked prettier before covering than mine did after covering. Learn a major lesson. If it ain't pretty before your cover it, it ain't gonna be pretty after you cover it. Finish the plane, cover it, then finish the finish. Nothing else works.

Absolutely. Your models will be 100x smoother with very little extra work or weight. I learned this trick when I was about 14, right after I learned about applying silkspan wet! Steve