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Author Topic: Polyspan / Silkspan  (Read 5212 times)

Offline Will Moore

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Polyspan / Silkspan
« on: April 21, 2025, 06:09:15 AM »
I have built and am currently finishing an Ares.
Which is a lighter covering;  Silkspan or Polyspan?
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Offline Ty Marcucci

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Re: Polyspan / Silkspan
« Reply #1 on: April 21, 2025, 07:16:35 AM »
Poly  span is lighter, but there are three silk span weights. Poly span takes less dope, based on my experience with it.
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Online Howard Rush

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Re: Polyspan / Silkspan
« Reply #2 on: April 21, 2025, 12:19:44 PM »
I have more opinion than experience, but here's my put:  Ares has a lot of ribs.  Silkspan is easy to sand through; polyspan isn't.  One would trowel a lot of dope on silkspan-covered ribs out of sand-through fear.  On polyspan there's merely a temporarily annoying fuzzy or two.  So I think you'd save dope weight with polyspan. 
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Offline Mike Quinn

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Re: Polyspan / Silkspan
« Reply #3 on: April 21, 2025, 02:53:18 PM »
Hi

Are there different grades of Polyspan.  If so, which is recommended and whats its weight per square ft?

Cheers

Mike
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Offline Jim Svitko

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Re: Polyspan / Silkspan
« Reply #4 on: May 01, 2025, 02:14:51 PM »
I do not know of polyspan being available in different weights/grades.  I have a package of Thermal Span, same as polyspan, but with no grain.  It is as strong chord wise as span wise.  The data on the package says 0.9 oz/sq yd.

I think Thermal Span is superior to regular polyspan and I would use that if you can still find it.
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Offline doug coursey

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Re: Polyspan / Silkspan
« Reply #5 on: May 01, 2025, 02:58:16 PM »
Quote from: Howard Rush on April 21, 2025, 12:19:44 PM
I have more opinion than experience, but here's my put:  Ares has a lot of ribs.  Silkspan is easy to sand through; polyspan isn't.  One would trowel a lot of dope on silkspan-covered ribs out of sand-through fear.  On polyspan there's merely a temporarily annoying fuzzy or two.  So I think you'd save dope weight with polyspan.
  Windy would put 10 or 12 extra coats over the ribs with a small brush to help from sanding through
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Online Howard Rush

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Re: Polyspan / Silkspan
« Reply #6 on: May 01, 2025, 03:15:40 PM »
Quote from: Jim Svitko on May 01, 2025, 02:14:51 PM
I do not know of polyspan being available in different weights/grades.  I have a package of Thermal Span, same as polyspan, but with no grain.  It is as strong chord wise as span wise.  The data on the package says 0.9 oz/sq yd.

I think Thermal Span is superior to regular polyspan and I would use that if you can still find it.

Larry Davidson sells two weights. You want the heavier.
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Offline wwwarbird

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Re: Polyspan / Silkspan
« Reply #7 on: May 01, 2025, 09:16:23 PM »
Quote from: Howard Rush on April 21, 2025, 12:19:44 PM
I have more opinion than experience, but here's my put:  Ares has a lot of ribs.  Silkspan is easy to sand through; polyspan isn't.  One would trowel a lot of dope on silkspan-covered ribs out of sand-through fear.  On polyspan there's merely a temporarily annoying fuzzy or two.  So I think you'd save dope weight with polyspan.

 Great advice.  y1

 As long as you put the correct side down fuzzies shouldn't be an issue. It's barely detectable, but you want the shiny side up.
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Online Ken Culbertson

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Re: Polyspan / Silkspan
« Reply #8 on: May 02, 2025, 05:51:38 PM »
Quote from: wwwarbird on May 01, 2025, 09:16:23 PM
Great advice.  y1

 As long as you put the correct side down fuzzies shouldn't be an issue. It's barely detectable, but you want the shiny side up.
I can save you a coat or two on the base by trying a trick I stumbled on.  Once you have the polyspan covered and tightened some give it a coat of dope then, while the dope is still wet, tighten it with the heat gun.  It glazes over and seals all of those nasty pin holes in one coat.

Ken
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Offline Motorman

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Re: Polyspan / Silkspan
« Reply #9 on: May 02, 2025, 07:30:05 PM »
Last time I bought polyspan from Larry Davidson he folded it up and mailed it in an envelope. Never got the creases out. I offered to mail him a tube with return shipping lable and he got offended because apparently his shipping method was perfect. I ordered the light because I use it over open bays and under Coverlite iron on. Maybe the heavy stuff won't crease in shipping? Good luck.

MM :)
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Offline john e. holliday

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Re: Polyspan / Silkspan
« Reply #10 on: May 02, 2025, 09:50:15 PM »
I've never had a problem with creases of a folded poly span.   When put down and shrunk with at least 4 to 6 coats of clear I can't see the folds/creases and almost all the creases at wing tips are gone. D>K
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Online Ken Culbertson

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Re: Polyspan / Silkspan
« Reply #11 on: May 03, 2025, 07:28:34 AM »
Quote from: Motorman on May 02, 2025, 07:30:05 PM
Last time I bought polyspan from Larry Davidson he folded it up and mailed it in an envelope. Never got the creases out. I offered to mail him a tube with return shipping lable and he got offended because apparently his shipping method was perfect. I ordered the light because I use it over open bays and under Coverlite iron on. Maybe the heavy stuff won't crease in shipping? Good luck.

MM :)
Curious, did you dope any of the structure before shrinking other than the edges?  I have never had an issue with wrinkles/folds coming out when shrunk, even when I heat shrink with wet dope.  I have had it with both silkspan and tissue applied dry.  Maybe it had been folded for a long time or was bad.

If memory serves (mostly it is double faulting lately) most kits used to come with the silkspan folded as did what I bought at what used to be called a hobby shop.  I can see however that folded and pressed might not be the best way to treat it.

Ken
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Offline john e. holliday

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Re: Polyspan / Silkspan
« Reply #12 on: May 03, 2025, 08:20:38 AM »
I never applied dope until the poly span was shrunk the first time.   Some time some areas needed to be hit with heat gun after a couple of coats of dope. D>K
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Online Ken Culbertson

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Re: Polyspan / Silkspan
« Reply #13 on: May 03, 2025, 08:54:37 AM »
Quote from: john e. holliday on May 03, 2025, 08:20:38 AM
I never applied dope until the poly span was shrunk the first time.   Some time some areas needed to be hit with heat gun after a couple of coats of dope. D>K
Try it, you might be surprised at how few pin holes there are.  Hitting full stretch with "wet" dope on it really helps.  Ends up the same but about 1-2 coats of dope less in the base.  Stumbled across doing this when I had to recover part of a wing in a hurry and just doped it.  Opps, I forgot to shrink it so I grabbed the gun and did it with the dope still wet.  It frosted over like you painted in the rain but when it was dry, it was both tight as a drum and without any of the trademark polyspan pin holes.

Ken
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Offline Larry Renger

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Re: Polyspan / Silkspan
« Reply #14 on: May 24, 2025, 07:48:24 AM »
If you get a case of the fuzzies, wet sanding with 2000 grit paper and another coat of clear will fix it. 🤠
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Offline Jim Hoffman

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Re: Polyspan / Silkspan
« Reply #15 on: May 25, 2025, 09:32:00 PM »
I’ve built three I-beamers over the years. Polyspan is my preferred covering. Stronger and more puncture resistant than silkspan. The resulting wing is pretty stiff in torsion.  I add extra coats of clear over the ribs to protect against sand through no matter what the covering used. 
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Online Dave_Trible

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Re: Polyspan / Silkspan
« Reply #16 on: May 31, 2025, 08:39:47 AM »
In my earlier years I preferred Ibeamers so did a number of them.   The sand through problem was irritating and had to do a lot of hole patching.   On a few I doped on a second narrow strip of silkspan over the ribs-sort of like the pinked cloth strips used on full scale over the ribs.   I might still go through the colored dope in spots but didn't damage the silkspan to the point of having to apply a patch.   Yes a lot of extra dope over the ribs will help too.   I have never tried Polyspan.   May be worth a try on my next Ibeamer-or just use silk.   I don't do as much (if any) wet sand and rubout stuff these days-mostly just well-retarded clear coats to save finish weight and a lot of elbow grease so for me it probably doesn't matter much.  I'd rather save a few ounces and hope the airplane flying better will gain back any loss in appearance points.  On my larger airplanes I'd have to put on another quart of clear to have enough depth to withstand a proper wet sand and polish.

Dave
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