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Old Apr 09, 2012, 04:14 PM
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Bill Smudge's Avatar
United States, KY, Bowling Green
Joined Jul 2011
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Question
Silkspan and Polyspan on fuselage

Howdy All,


Getting ready to cover my fuse, soon I hope..

Aiming to cover the planked areas with silkspan, then the open stringer areas with Polyspan for strength and puncture resistance.

What is the best technique to use, where the two different covering media merge? Hoping to have a seamless finish.

I expect you can finish and sand the silkspan down to a feathered edge but I've never used Polyspan before and I'm not sure about feathering the edges.

Please see my picture for details.

Thanks much for any advice.

Bill
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Old Apr 09, 2012, 04:24 PM
Where's the lift?
dgliderguy's Avatar
United States, WA, Snohomish
Joined Mar 2001
2,920 Posts
My recommendation is to cover the whole thing with Polyspan... one piece for the left side and one piece for the right side. Polyspan can be stretched like plastic film if you lay it down with the help of a covering iron. I use nitrate dope, or sometimes polycrylic (Minwax), for sticking it down.

If you must combine the two materials, you can smooth out the overlaps with vinyl spackle prior to prime and paint.
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Old Apr 09, 2012, 04:40 PM
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
12,457 Posts
Don't try to sand/feather, Poly-Span, Bill. It is a polyester fiber, and will not sand. You will end up with a raised fiber, that is hard to get rid of. I have fine sanded it with VERY worn 400W/D. But very lightly.

Poly-Span seams can be hidden with a strip of feathered silk-span. And I agree with gliderguy, the texture of both mediums is very close. and equal to using a grade of med silkspan as far as weight is considered. So, just use the poly-span, and then no worries of seams.

My Stahl Apache is 100% Poly-Span. And you don't need expensive aircraft nitrate to seal poly-span or silk-span. Regular hardware store lacquer works just fine, thinned 50%, or more. I did a thread on silk-span. The sealing of poly-span is the same.

http://www.rcgroups.com/forums/showthread.php?t=1598074

Fuzz
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Old Apr 09, 2012, 04:45 PM
The Hun in the Sun
vonJaerschky's Avatar
Canada, BC, Comox
Joined Nov 2003
7,472 Posts
I used the polyspan/silkspan method on my Bucker Jungmeister, and it came out great. Apply the polyspan over the open framework first, then the silkspan on the solid sections , leaving about a 1/4"-1/2" overlap. You can sand the silkspan to a feather edge and have it magically disappear, showing no seam at all. You can't sand polyspan, because it will raise frizzies that are impossible to remove with more sanding. Have a look at post #252 on this page.

I applied the polspan by ironing it on using Sig Stix-it. Then I applied 2 or 3 coats of clear nitrate dope on the polyspan and all the balsa. Then I applied the silkspan wet, doping only around the perimeter. Once it has shrunk and was dry, I applied 4 more coats of clear dope, carefully feather-edging the seam each time with 400 grit paper.

Using Polyspan over the sheeted sections does work fine, but if you want an absolute smooth, metal like surface, I would go with silkspan. I found I can't get polyspan to look as smooth on sheeted areas. When it's all done, it looks a little like this:
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Old Apr 09, 2012, 05:34 PM
Where's the lift?
dgliderguy's Avatar
United States, WA, Snohomish
Joined Mar 2001
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Von,

That Bucker is a nice piece of work. Good skills there, man. Well worth the obvious investment in time and patience.
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Old Apr 09, 2012, 07:14 PM
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Bill Smudge's Avatar
United States, KY, Bowling Green
Joined Jul 2011
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Looks like I'll follow Von's method, Poly then the Silkspan.

His Bucker is gorgeous.

Shinny side up on the polyspan as I understand it.

Does Polyspan shrink the same in all directions?

Thanks for the info guys!!

Bill
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Last edited by Bill Smudge; Apr 09, 2012 at 07:17 PM. Reason: couple of other questions
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Old Apr 09, 2012, 09:55 PM
The Hun in the Sun
vonJaerschky's Avatar
Canada, BC, Comox
Joined Nov 2003
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Thanks for the comments on the Bucker, guys. Much appreciated. It's my favourite model for sure!

Shiny side up is a good basic rule for Polyspan, although sometimes it's hard to tell which side is shiny and which isn't. If the material arrives rolled up, the top surface is the outside of the roll, like plastic coverings. It shrinks pretty evenly. It has a definite grain, which you generally want to run parallel with the long edge of whatever you are covering. I shrink it with a heat gun, but you need to be careful you don't over-shrink it. What happens then is that it pulls itself apart and leaves larger gaps in the natural weave of the material, which means more dope to fill it, or even a patch of silkspan to cover any bigger holes. (Don't ask me how I know!)
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Old Apr 09, 2012, 11:44 PM
Where's the lift?
dgliderguy's Avatar
United States, WA, Snohomish
Joined Mar 2001
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I second that motion about the shiny side-- it's easier than you think to miss this, so scrutinize your cut piece well before laying it down. I've been covering with Polyspan for many years now, and on my most recent job I completely missed this on one wing outer panel. Fuzzies!!

'Annoyed' is when you get a corner wrinkle that won't iron out. Downright 'pistoff' is when you lay the fuzzy side up and don't catch it until the coats of dope show your mistake, and you have to rip it off and do it over. Don't let it happen to you!
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