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02-18-2009, 10:52 AM
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Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,861
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Basic Fiberglass cloth cutting question
OK,
Silly question of the day. Once I cut a section of BID cloth off the roll on a 45 deg bias, how should I orient the subsequent layups that I cut out. Like #1, #2, or it doesn't matter. Thanks!

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Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
Last edited by Auburntsts : 02-18-2009 at 11:07 AM.
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02-18-2009, 11:28 AM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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I'd keep the bias at 45 all the time. the cloth is stronger, both thread directions are holding something. if you cut a long skinny strip with threads oriented 90 and 180 degrees the threads running parallel aren't doing very much if your fabric is covering and bridging a joint.
what are you working on? are you cutting long skinny strips? (like 1-2 inches wide, a foot+ long)
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02-18-2009, 11:41 AM
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Join Date: Aug 2005
Location: Pasadena CA
Posts: 2,484
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Layups are to be alternated 45? then 0? then 45?. I would always have a odd number, with 45? on the two outside layers. Either 3, 5 or 7 ply layups.
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Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
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02-18-2009, 11:46 AM
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Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,861
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Quote:
Originally Posted by osxuser
Layups are to be alternated 45? then 0? then 45?. I would always have a odd number, with 45? on the two outside layers. Either 3, 5 or 7 ply layups.
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So to make sure I understand the orientation using my example, for a 3-ply layup you recommend I cut plys 1 and 3 like my #1 and ply 2 like my #2. Is that right?
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Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
Last edited by Auburntsts : 02-18-2009 at 11:48 AM.
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02-18-2009, 12:11 PM
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Join Date: Jan 2005
Location: The Beautiful NJ Shore
Posts: 409
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Always like #1. The ONLY orientation is like #1. I've done Hundreds of layups. After the initial corner cut, All subsequent cuts off the roll are properly oriented. Layups are not done 45-0-45. They are all 45.
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Greg Piney
RV-8 2547
Empennage Done!
Beginning Fuselage Final Assembly!
(Tub finished, on to Landing Gear).
Last edited by gpiney : 02-18-2009 at 12:15 PM.
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02-18-2009, 12:47 PM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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Quote:
Originally Posted by Auburntsts
So to make sure I understand the orientation using my example, for a 3-ply layup you recommend I cut plys 1 and 3 like my #1 and ply 2 like my #2. Is that right?
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what are you working on? cessna (columbia) and lancair don't do any of the 45-0-45 layups for long skinny bid tapes. all on the 45, all the time.
edit- i've also done hundreds of layups, in the lancair factory. from 2 layers to 12 or 16 (I forget, but it is the reinforcement for the IV foot peg, and it is really (no really) thick) but that is composite based planes, and that is why i tried to give an explanation for having fibers run 45 all the time instead of 90 and 180 (or zero if you want to look at it that way). That is why i've asked what you are working on. how many layers do you think you will lay down on this part you are doing?
i don't see much explanation for WHY to do a 45-0-45 style.
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Last edited by Danny7 : 02-18-2009 at 12:56 PM.
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02-18-2009, 01:18 PM
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Join Date: Jan 2005
Location: Tampa, FL
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I'm slowwwwwly working my RV-10 emp fairings, but my question was just general recommended how-to rather then aimed at a specific layup. I had assumed that my #1 example was the way to go, where I keep the layup edges parallel or perpendicular to the 45 bias. It made the most sense to me, but figured I'd ask those with experience before I unecesssarily screwed something up. Thanks for the replys!
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Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
Last edited by Auburntsts : 02-18-2009 at 01:35 PM.
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02-18-2009, 01:30 PM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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Quote:
Originally Posted by Auburntsts
I'm slowwwwwly working my RV-10 emp fairings, but my question was just general recommended how-to rather then aimed at a specific layup. I had assumed that my #1 example was the way to go, where I keep the layup edges parallel or perpendicular to the 45 bia. It made the most sense to me, but figured I'd ask those with experience before I unecesssarily screwed something up. Thanks for the replys!
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sweet.  in general, always 45
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02-18-2009, 02:27 PM
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Join Date: Nov 2006
Location: Bennington, Vermont USA
Posts: 1,301
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Depends where you want the strength
0 deg strips - along the length of the roll - are strongest in tension and compression
90 deg strips - across the width of the roll - are slightly less strong in tension and compression because the "fill" fibers in a woven cloth tend to be less straight than the "warp" fibers - not a significant factor for non-structural fiberglass but carbon drawings often specify a required warp fiber direction - a bit like grain direction for critical metal parts
45 deg strips are strongest in shear - they also drape and form into and around corners more easily - the down side of this is that they can also be a bit "squirrelly" to handle, especially if you pre wet them on the table.
45 deg strips can make less efficient use of the material
Cleats and other shear carrying brackets and angles tend to be 45 deg
If you want to mimic a metal's strength in all directions over a big surface - e.g. a cover plate or cowling - it is common to mix 0 deg and 45 deg plies - be careful to make the plies symmetric about the mid plane though if you don't want a potato chip!
For obvious tension or compression members like wing spar caps or struts it is most efficient to use rovings of straight fibers with a minimum amount of 90 or 45 fabric to stop the laminate splitting and to help tie it to the spar web and/or skin
For the windshield strip on my -6 tip-up I mixed zeros and 45s - but I don't think it matters
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02-18-2009, 03:18 PM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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Quote:
Originally Posted by jsharkey
45 deg strips are strongest in shear - they also drape and form into and around corners more easily - the down side of this is that they can also be a bit "squirrelly" to handle, especially if you pre wet them on the table.
45 deg strips can make less efficient use of the material
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if you wet them on a table, use film plastic to sandwich them. this way you can also roll out any bubbles and excess resin. cut the whole thing with rotary cutter, and you've got perfect edges, easy to handle even when 3-4 feet long strips.
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