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General control line discussion => Open Forum => Topic started by: Jim Catevenis on February 01, 2019, 11:08:28 AM
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Question-Has anyone applied a couple of coats of nitrate on the flaps, stab and elevators before adhering Ultracote? I seem to remember talking
with someone at Brodak's a few years ago and they indicated that they did this. Anyone have experience with this process? Comments/suggestions please.
Thanks,
Jim Catevenis
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I use a really thin coat of dope (30-40%) as a sanding aid, to knock the balsa fuzz off. But if I use too much dope, the plastic covering bubbles underneath. Not sure if the covering heat is out gassing the dope or the dope has created a barrier that prevents the air from passing through the balsa. Maybe both.
Out of FF habit, I do dope all the structure (ribs, spars etc.) to minimize humidity changes. Probably totally unproven, but I do it anyway.
Norm
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Jim I have applied Nitrate dope around the perimeter of the wing thinking I was going to silkspan it and then changed my mind and put Ultracote over it instead and never had any adverse results. I did sand it well though before I applied the Ultracote. Under normal circumstances, I would not apply dope before applying a shrink type covering.
Mike
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I had a weird experience one time regarding putting Monokote over an old plane that had been finished with nitrate dope. Here goes.... I ended up with a pollywog Chief that was in a storage locker after it's owner/builder passed away. The tissue wing covering was a mess and there was a large hole on the turtle deck. I carefully stripped off as much of the wing covering as possible. I then repaired the fuselage and covered repair with tissue and dope.
After sanding the wing with 320 paper then 400, I went about covering the wing with transparent red Monokote. Everything was great until I got to the wingtip where higher heat was needed. I started to smell something burning. Seems as though the heat from the sealing iron was enough to ignite the dope and the tip was on fire. I had a cup of coffee nearby and extinguished the burning wood. I repaired the burnt tip and continued covering at a much lower temperature. So, be careful with heat over nitrate doped airframes.......Skip
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I have learned over the years to NEVER put anything on the balsa before I use Monokote.
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Question-Has anyone applied a couple of coats of nitrate on the flaps, stab and elevators before adhering Ultracote? I seem to remember talking
with someone at Brodak's a few years ago and they indicated that they did this. Anyone have experience with this process? Comments/suggestions please.
I would not do this under any circumstances. At best, you will get away with it without causing bubbles, but as far as I can tell there is no advantage at all to it. Proper technique on properly-sanded balsa doesn't need anything like this. I have tried it, it was a complete mess.
If you *DO* try it, let it dry (preferably under warm conditions) for a long time, to allow the dope to outgas to the maximum extent possible before you neat it to adhere the covering.
Brett
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I have learned over the years to NEVER put anything on the balsa before I use Monokote.
Crist,
If I recall correctly, you have used nitrate on silkspan on balsa at the wing center joint, and then covered that with monokote. Not monokote directly on balsa with nitrate. That seemed to work ok.
Fred
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This all may have started when the first "primer" for iron on coverings came out and I think that was Balsa-Rite by Cover-Rite. I remember customers asking about it at the shop years ago, and that it smelled like dope to them, and asked me if they could use dope instead and I cautioned against it. It had a strong smell but I could tell it wasn't dope of any kind. Especially when the instructions say to thin it with acetone! For this type of work, I prefer SIG Stix-It.
Type at you later,
Dan McEntee
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This all may have started when the first "primer" for iron on coverings came out and I think that was Balsa-Rite by Cover-Rite.
Correct me if I'm wrong, but I think Balsa-Rite was a product intended for better adhesion of iron on coverings? I think it was supposed to work as a heat activated adhesive or something? I know I used to use it years ago on R/C models as a prep for applying Coverite covering material, I think that was why.
Whatever the case, do as Crist says, if you've seen his covering work you'll know why. y1
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Crist,
If I recall correctly, you have used nitrate on silkspan on balsa at the wing center joint, and then covered that with monokote. Not monokote directly on balsa with nitrate. That seemed to work ok.
Fred
Fred, you're right. I forgot about that. It does bubble where the silkspan is. I use minimum heat there. I would never cover a solid flap with Monokote with underneath except bare balsa.
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I want to thank everyone for their comments and it has convinced me not to apply nitrate before covering
the solid surfaces. It has been several years since I have built or covered anything (medical issues) so I am trying to see if
there has been any new procedures. Thanks again everyone.
Jim Catevenis
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I did it on my older models and it worked fine.
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I'm curious to know WHY you would want to do this?
From my point of view it seems to be an extra finish step that's not really required, and may cause bigger issues later on.
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I thought it made ultracoat stick better. I guess it worked okay because I still fly those planes 15-16 years later.
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Well here's my nickel's worth! If you're repairing a well used and perhaps oiled plane, first draw all the old goo out with K 2R or a slurry of talcum power and alcohol or corn starch, followed by heat and paper towels. Once its as dry and clean as you can make it I use Balsa Rite to seal out or in any remaining oily residue. Apply the iron on covering right over the Balsa Rite with the lowest heat needed to make the stuff stick. This has worked for me in resurrecting many an oily bird of which many are still serving me quite well!
Phil Spillman