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Author Topic: Polyspan vs silk torsional stiffness  (Read 795 times)

Offline Dennis Toth

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Polyspan vs silk torsional stiffness
« on: July 10, 2018, 07:44:35 PM »
Guys,
Which material, polyspan or silk, offers the strongest torsional stiffness? Which one will be the lightest?


Best,    DennisT


Offline Mike Haverly

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Re: Polyspan vs silk torsional stiffness
« Reply #1 on: July 10, 2018, 09:34:34 PM »
Answers:  Polyspan and Polyspan.
Mike

Offline Dennis Toth

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Re: Polyspan vs silk torsional stiffness
« Reply #2 on: July 11, 2018, 05:29:23 PM »
If polyspan do you use taunting type clear (i.e. Sig Supercoat Clear) or non-taunting (i.e. lite coat or Brodak Clear) to get the a tight. torsion resistant covering? How many coats before switching (if at all) from taunting to non?

Best,    DennisT

Offline Mike Haverly

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Re: Polyspan vs silk torsional stiffness
« Reply #3 on: July 11, 2018, 05:45:55 PM »
Use non tautening for putting it on and one coat of tautening on open bays after the weave is sealed.  I actually use nitrate for adhesion then butyrate.  All butyrate will work but is not as sticky.
Mike

Offline Dennis Toth

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Re: Polyspan vs silk torsional stiffness
« Reply #4 on: July 12, 2018, 06:51:42 PM »
OK, I have read that some builder have aligned the polyspan grain with the sweep of the leading edge to get a little additional torsional stiffness. Since the ship I am covering has a straight leading edge and swept trailing edge I thought I'd align with the TE to get the same effect.

Best,    DennisT

Offline Jim Svitko

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Re: Polyspan vs silk torsional stiffness
« Reply #5 on: July 12, 2018, 06:58:42 PM »
There is a product called ThermalSpan.  It is identical to polyspan in all respects except it is as strong in the chord-wise direction as span-wise.  It has no "grain".  This feature may help regarding torsional stiffness.

Offline Target

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Re: Polyspan vs silk torsional stiffness
« Reply #6 on: July 12, 2018, 07:29:19 PM »
In theory if the material has a grain, I'd think laying the grain at a 45 degree angle to the leading edge on top, and on a 45 degree the other way on bottom would provide the most torsional stiffness.
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Chris
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Online Lauri Malila

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Re: Polyspan vs silk torsional stiffness
« Reply #7 on: July 13, 2018, 04:06:49 AM »
In theory if the material has a grain, I'd think laying the grain at a 45 degree angle to the leading edge on top, and on a 45 degree the other way on bottom would provide the most torsional stiffness.

Yes in theory, but polyester tissue has fibers running mostly in one direction so you end up in asymmetric fiber orientation.
Besides, when fibers are running diagonally, covering sags more between ribs, so you donít really win much. L

Offline Target

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Re: Polyspan vs silk torsional stiffness
« Reply #8 on: July 13, 2018, 07:26:26 AM »
Hmmm, for some reason, i thought we were talking about flap stiffness only. I'd be fine with diagonal on solids, but certainly not do that on open bays. Oops.
I must have been thinking of another thread!

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Target
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Offline Dennis Toth

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Re: Polyspan vs silk torsional stiffness
« Reply #9 on: July 13, 2018, 01:50:28 PM »
OK, will just keep grain aligned along the straight leading edge. Since the wing is removable I will do the bottom then top in just two pieces. Will use Sig Supercoat for base then switch to litecoat (I have a lot of this that I need to use up). Has anyone use the Aerolite filler in say the 4th of 5th clear coat to fill the grain and establish a smooth substrate for the color?

Best,   DennisT

Offline Dennis Toth

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Re: Polyspan vs silk torsional stiffness
« Reply #10 on: July 18, 2018, 05:41:01 PM »
Well I finally made up my mind and will go with 6mm silk from Thai Silk. It arrived today and I did compare it to the K&S heavy duty silk and the 8mm Thai silk I had from last year. The 6mm is just a tad less sheer then the K&S but not as much as I thought it would be. Comparing to the 8mm it is a tad more sheer but the difference in the weight between the two is also very small. My conclusion is all of them should be good.

I have given the raw wing two coats of Sig Butyrate lite coat 50/50 to seal the grain and not shrink. Next will sand of the fuzz and get ready to apply the silk with Sig Supercoat clear (60/40 thinner to dope to start then go to 50/50) which will tighten up the silk. On the El D it took about 8 total coats and it came out pretty good. I intend to paint this ship and next will have to decide what the trim will be.

Also, got a fresh Preval Spray package with the new trigger handle (check Home Depot and Amazon for this system). Next will get some 2X rattle can death paint.


Best,   DennisT

Offline Dennis Toth

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Re: Polyspan vs silk torsional stiffness
« Reply #11 on: July 22, 2018, 06:08:37 AM »
Question for the group. When we apply dope to our coverings (silk, silkspan, polyspan) what is actually shrinking to get it and keep it tight? Assuming it is reasonably tight and smooth to start I seem to me that the dope is what makes it drum tight not the fabric/material shrinking as it dries or cools. This would support the guys that are applying dry and getting covering just as tight as the wet method. What do you think?


Best,    DennisT


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