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Building Tips and technical articles. => Paint and finishing => Topic started by: Neville Legg on November 07, 2009, 01:50:13 AM
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I've used non shrinking dope on free-flight models where the structure was light and prone to warping, but not on stunters.
I assume it sands like shrinking dope? The next model I build will have no open fabric covered areas, so I intend to used non shrinking dope throughout.
Anyone done this?
Cheers Neville
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If you have no open bay areas to worry about, the low shrink (or no shrink) dope will work just fine. I use mostly low shrink anyway. Sands and finishes exactly the same.
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Are you going to use non tautening butyrate, or nitrate dope? I've read here on the forums that Nitrate dope has more solids in it and fills balsa better, the flip side is that it does weigh more. On my next plane (the Chipmonk) I will use nitrate as a base, with butyrate as the top. I'm thinking it will have open bays. I'm curious how sheeting the wing will add to the total weigh, if it does.
Brian
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I'll use nitrate dope as its readily available here in the UK. If sanded well, I should use fewer coats of dope on a fully sheeted wing? Lightweight jap tissue, doesn't need many coats to get a smooth finish! Its all in the sanding, so said Don Bambrick in his Fury article in Flying Models, not in loading on tons of dope and filler! We shall see ;D
Cheers Neville
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Are you going to use non tautening butyrate, or nitrate dope? I've read here on the forums that Nitrate dope has more solids in it and fills balsa better, the flip side is that it does weigh more. On my next plane (the Chipmonk) I will use nitrate as a base, with butyrate as the top. I'm thinking it will have open bays. I'm curious how sheeting the wing will add to the total weigh, if it does.
Brian
Nitrate dope is not a higher solids product than butyrate dope. Coat for coat it does not weigh more than butyrate dope. Nitrate dope was the first dope developed around the first world war and was the standard until after WWII. Butyrate dope was developed to provide a dope system that ignited less easily and burned more slowly than nitrate dope. Nitrate dope is a nitrocellulose product which is chemically similar to gunpowder, igniting easily and burning almost explosively; butyrate dope, which is cellulose-acetate-butyrate, is more difficult to ignite and burns much more slowly...a big deal if you are flying along in your Aeronca Champ at 5,000' AGL and develop an in-flight fire.
Nitrate will develop slightly more film tension as it shrinks than will butyrate, but the tensile strength of the dried film is less than that of butyrate. Butyrate is fuel resistant whereas nitrate is not fuel resistant. I have not found that there is any difference in "sandability" of nitrate or butyrate in years of using it on both full-scale airplane restorations or on my models. Whether you start with nitrate or butyrate comes down to personal preference. The only requirement for using nitrate dope in aviation is for the first coats on the Ceconite process as specified in the Ceconite STC for full-scale, type-certificated airplanes. If your personal preference is for using nitrate for the initial coats on your models then by all means go ahead; there just isn't any real reason to do so except for your personal preference.
Tautening type dopes, both nitrate and butyrate, will sand more easily than the non-tautening types due to the plasticizer in the non-tautening dopes. The plasticized dopes tend to "ball up" on the sandpaper if you are sanding dry. However, I have not had any problems sanding the non-tautening types. I sand wet using water with a drop or two of dishwashing detergent in a quart or so of water and have no problems with the non-tautening types.
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Bill, thank you for that very informative reply. If you go into any model shop in the UK you will only find nitrate dope, so that's what I've used over the last 45 years or so! I have used Butyrate when I can get it, I like the fact that it is far more flexible than Nitrate, and fuel proof! Nitrate cracks after a while on silk, so that's why I'm going to sheet as many wings as possible ;D
Cheers Neville
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There is a Randolph Aircraft Products distributor in Devon, England. Google Randolph Aircraft Products for details.
Don
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Thanks for that I'll have a look ;D
Cheers Neville
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Don, I've just had a look at that supplier in Oakhampton Devon, their dope is cheaper than model shop prices! ;D Trouble is Devon is about 250 miles from me!
I do go down that way now and then so I'll call in and get some, thanks for the info. When my dad was de-mobbed from the RAF in the '50's he came home with gallons of dope that lasted quite a while, I think it finally went brown as the cans rusted, and became unusable.
Cheers Neville
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Don, I've just had a look at that supplier in Oakhampton Devon, their dope is cheaper than model shop prices! ;D Trouble is Devon is about 250 miles from me!
I do go down that way now and then so I'll call in and get some, thanks for the info. When my dad was de-mobbed from the RAF in the '50's he came home with gallons of dope that lasted quite a while, I think it finally went brown as the cans rusted, and became unusable.
Cheers Neville
Neville, I don't know if your Devon dealer ships dope in the UK,but if they do, and have HazMat fees for it, it may be cheaper to buy quarts of your dope.Both US Aircraft Spruce East and West ships Randolph here in the states, and if you order in quarts, they don't charge HazMat fees for shipping it. If you do buy a gallons, its about 25-30 bucks extra for HazMat(hazardous material handling)so it may be the same over there.Just a thought.Could save you a trip.
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Looks Like I can have it posted by the quart, more likely a litre in the UK. I'm always concerned about buying to large an amount of anything degradable!
Cheers Neville