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Applying Dope to GTM Fabric Question

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Applying Dope to GTM Fabric Question

Old 10-10-2011, 06:58 AM
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JKEpps
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Default Applying Dope to GTM Fabric Question

I'll call GTM later today to get their input (hopefully they're open on Columbus Day), but until then, I wanted to see if anyone had any thoughts. I'm almost at the stage where I am about to cover my Balsa USA 1/3 scale Fokker D.VII. I ordered Randolph dope from Aircraft Spruce, but somehow I goofed (completely my mistake) on the order. I ordered Tautening Nitrate, and Non-Tautening Butyrate. Then When I went back to re-read the instructions from GTM on how to apply their Lozenge fabric, I saw I got it backwards. GTM says to use Non-tautening Nitrate, and Tautening Butyrate.

So the question is, am I OK to use what I have, or should I get what GTM recommends in their instructions?

Thanks in advance,

-Jorden
Old 10-10-2011, 07:02 AM
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LesUyeda
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Default RE: Applying Dope to GTM Fabric Question

"So the question is, am I OK to use what I have, or should I get what GTM recommends in their instructions? "

I tend to believe that the manufacturer/seller has reasons for their recommendations. They REALLY want you to be successful with their products, so you will come back.

Les
Old 10-10-2011, 07:34 AM
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Default RE: Applying Dope to GTM Fabric Question

If Iremember correctly Iused taughtening nitrate and butyrate both when Iused the Glen Torrance fabric. The type of dope didnt seem to be a problem. Idid have trouble due to my own mistake of not pulling the fabric as tight as Icould when Iapplied it to the structure. Be sure to get the fabric as tight as you can when you stick it on or it may not shrink enough and you will get sags. Dont ask how Iknow this. Another thing to be aware of is the process looks terrible in the middle. You will reach a point after the nitrate goes on that the fabric will look terrible. Dont panic, move on the butyrate and things should smooth out nicely.

Good luck. Ithink you will be happy with the result. GT lozenge is the best stuff in the world.

Dave S.
Old 10-10-2011, 07:36 AM
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Default RE: Applying Dope to GTM Fabric Question

A quick addition to my previous note. Iused tautening dope of both types. Ithink you had better use the tautening butyrate because the butyrate coats are when the fabric really smoothed out for me. I dont know if non tautening dope will do that.

Dave S.
Old 10-10-2011, 08:09 AM
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JKEpps
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Default RE: Applying Dope to GTM Fabric Question

OK, just spoke to the good folks over at GTM. Was told that others have done it with what I have, and have had good results. Also it seems the full-scale guys like using the non-tautening Butyrate because it won't continue to tighten over time. In any case, he recommended Sig's products, that's all he uses on his models. I remember at the time when I bought the kit about a year ago, I was going to buy Sig dope, but it wasn't available. Apparently now it is, and Sig is doing well due to new ownership. Well, I guess I have a decision to make. What I'll do is test it with what I have in a spare wing, and see what happens. Worst case is that I'll have to order it from Sig.

Thanks.
Old 10-10-2011, 08:15 AM
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MaineBear
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Default RE: Applying Dope to GTM Fabric Question

Although I've not built anything from GTM, I'm sure the recommendation to use non-tautening dope is due to the strength of the a/c's framework/construction. Using regular nitrate or butyrate dope (i.e. non-tautening) would very likely warp the framework... and I sure would not want to take a chance of that happening.

Good luck!

Dick
Old 10-10-2011, 08:51 AM
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BobH
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Default RE: Applying Dope to GTM Fabric Question

Normally Butyrate tightens more than Nitrate when both are not non-tightening. I think you'll be ok using what you have.
As others have said make sure your fabric is fairly tight when its still wet. Dope will tighten the fabric but its not like iron on covering. Just keep that in mind.
Old 10-10-2011, 10:50 AM
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Default RE: Applying Dope to GTM Fabric Question

Also don't forget to coat the tops of your spars with bee's wax to keep the fabric from sticking to the spars. Glenn mentions that
someplace in his instructions.

Good luck with covering. I know you will be pleased with the results.

Mike
Old 10-10-2011, 12:18 PM
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destrat
 
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Default RE: Applying Dope to GTM Fabric Question

JKEpps:

So far everyone in this thread about gave good answers to your dope question . I have done two 1/4 scale Pfalz's a D-IIIa, D-XII,with Glenns fabric using Sig's dope and have had excellent results! I did use the low shrink butyrate with good results. Like they said things look a little rough at first, but press on, it will work! One little trick I used when sewing the fabric together is to use a double needle in the sewing machine, it makes for a real nice stitch about 3/16th's inch apart, and if you have trouble sewing a straight line there is a magnetic type fence you can put on the sewing machine and run the seam up against. Good luck!
Old 10-10-2011, 12:30 PM
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Default RE: Applying Dope to GTM Fabric Question

Bear in mind again as the dope ages taughtening or non-taughtening it will continue to shrink. after a few years it could be tight enough to damage the structure. 

I have seen this 1st hand on full scale airplanes! a Rearwin Cloudster (literally broke the ribs) and a Stearman (the fabric split at stressed areas due to the over tightening). 

Non-taughtening is the best way to go. 
Old 10-10-2011, 02:47 PM
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Default RE: Applying Dope to GTM Fabric Question

All good answers. One thing to understand is that non-tautening dope is like decaf coffee. Decaf coffee still has caffeine and non-tautening dope still shrinks. My only concern about using tautening nitrate at the very beginning of the process is the possibility it might pull the edges of the fabric off of the airframe.
As others have said, don't freak out if it looks horrible after the first coat or two of dope, "It will get better".

J

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