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09-03-2008, 07:30 PM
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Join Date: Feb 2005
Location: Bridgewater, MA - KPYM
Posts: 458
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Which carbon fiber tape?
I am working on my RV-8 canopy windscreen and would like to add some carbon fiber tape to the canopy bow. I am sure that at some point in time i will grab it getting in or out of the plane and I would like to strengthen the glassed area.
After reading all the specs, I am even more confused as to which weave and weight would work best.
US Composites seems to have the best selection. For those who are familiar with carbon fiber, which cloth tape would you suggest? Should I consider Kevlar as well?
choices are: http://www.shopmaninc.com/carbonpage.html
Thanks in advance for your suggestions.
Mike Draper
RV-8 N468RV
-working on the canopy
Last edited by drill_and_buck : 09-06-2008 at 05:57 AM.
Reason: spelling
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09-03-2008, 09:50 PM
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Join Date: Jun 2005
Location: Federal Way, Wa
Posts: 264
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Depends - but don't use Kevlar!
Do you want an outer cosmetic layer or do you want stiffness and plan to paint the bow? The unidirectional carbon tape will provide stiffness parallel to the bow, but will provide no strength perpendicular to the bow. It will easily crack parallel to the fibers when gripping it with your hands. This material is parallel graphite tows tied together with non-structural fibers.
Any of the other fabrics can be used depending on your preference for thickness. The thinner fabics allow a mixing of glass and graphite without making the bow layup too thick. A good basic weave is the plain weave. It should drape fine for the bow contours.
If you want a cosmetic finish, just pick the weave that you like the best.
Don't use Kevlar. Epoxy does not bond well to Kevlar and can easily be delaminated. Plus you can't sand it, and it is not as stiff as the graphite. A kevlar laminate can easily be peeled abart ply by ply.
One other tip, if you use carbon fiber with fiberglass, make the material layup symmetric about the center of the layup stack by both material type and orientation. In other words, if you want a 0/90 carbon last ply, put a 0/90 ply down also as the first ply. Otherwise, as the cured laminate changes temperature, the different materials and fiber directions will cause the laminate to warp due to the mismatch in coefficients of thermal expansion.
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Brice
RV-9A 90897 FLYING
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09-03-2008, 10:05 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Mike, in that application I'd suggest carbon is a lot of trouble/expense for very little gain.
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Dan Horton
RV-8 SS
Barrett IO-390
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09-04-2008, 04:13 AM
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Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,692
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Tips FOR kevlar?
Quote:
Originally Posted by BJohnson
Don't use Kevlar. Epoxy does not bond well to Kevlar and can easily be delaminated. Plus you can't sand it, and it is not as stiff as the graphite. A kevlar laminate can easily be peeled abart ply by ply.
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Brice,
It's obvious that you have direct experience with composites. Since I have a "free" roll of plain weave Kevlar sitting in the shop, I am curious if there are techniques to successfully use it. Heck, I already forked over the cash for the good scissors! 
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Bill Pendergrass
ME/AE '82
RV-7A: Flying since April 15, 2012. 850 hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
Unpainted, polished....kinda'... Eyeballin' vinyl really hard.
Yeah. The boss got a Silhouette Cameo 4 Xmas 2019.
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09-04-2008, 08:10 AM
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Join Date: Jan 2008
Location: Atlanta, GA
Posts: 240
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make bulletproof clothes! 
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Ian
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09-04-2008, 11:39 AM
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Join Date: Jun 2005
Location: Federal Way, Wa
Posts: 264
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Other uses of Kevlar
Other that ballistics, including fan containment structures for turbofan engines, the best use of Kevlar I have seen is as a peel ply. I have placed Kevlar/epoxy prepreg between two stacks of carbon/epoxy prepreg with the intent to later separate the two carbon laminates after cure. Once cured, the two pieces separate very easily at the Kevlar layer by starting peel with a knife wedge at the Kevlar. The Kevlar ply can then be removed without tearing as a single piece.
Kevlar is great for energy absorption..... when used in tension where one does not have to rely on the shear properties for resin to fiber adhesion.
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Brice
RV-9A 90897 FLYING
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09-04-2008, 02:13 PM
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Join Date: Feb 2005
Location: Bridgewater, MA - KPYM
Posts: 458
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Overkill?
Brice, thanks for the briefing, it was very helpful.
Dan, you raise an excellent question. Is it really necessary to reinforce the canopy bow on the RV-8?
For those RV-8ers who *haven't* added any carbon fiber to the canopy bow, have you ran into any issues?
Mike Draper
RV-8 N468RV
- working on the canopy
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09-04-2008, 04:40 PM
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Join Date: Feb 2006
Location: Friendswood, TX
Posts: 68
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I have a four year old -8 with the canopy bow made of plain old fiberglass. It is plenty strong. No cracks. Just use enough layers to make it stiff without getting to thick.
David
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09-04-2008, 04:58 PM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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Quote:
Originally Posted by BJohnson
One other tip, if you use carbon fiber with fiberglass, make the material layup symmetric about the center of the layup stack by both material type and orientation. In other words, if you want a 0/90 carbon last ply, put a 0/90 ply down also as the first ply. Otherwise, as the cured laminate changes temperature, the different materials and fiber directions will cause the laminate to warp due to the mismatch in coefficients of thermal expansion.
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Have you seen this happen? I ask because this is the first i have heard of it, and i've worked on some legacys, which often have fiberglass and carbon mixed. I don't have years of experience with composites, just months (albeit full time ) and i think i would have remembered something like this if someone told me. maybe no-one ever told me ; )
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09-04-2008, 05:24 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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<<Brice, thanks for the briefing, it was very helpful.>>
Yeah, and I wish you would write more often. I very much enjoy professional input.
<<Dan, you raise an excellent question. Is it really necessary to reinforce the canopy bow on the RV-8? >>
.....or any other slider? Depends. Some folks can break a bowling ball in a rubber room.
Here's why I said you were going to a lot of trouble for not much gain. Carbon tends to be seen as some sort of super fabric. It's not; it merely has different properties as compared to the other choices. Quantifying those properties and applying them is important.
Brice, check me here. A bi-directional carbon/epoxy laminate is stiffer than glass/epoxy (roughly 3 to 4 times). However, it is not vastly stronger (maybe 1.5 times).
So, a little country-boy analysis for the windshield lip. Assume the plans version is 6 plies of 9 oz glass tape (I dunno, is it?). The fabrics you're likely to use are all about 0.010 inch thick.
Maybe you use 9 plies of glass tape instead of 6 plies. Three additional plies of 9oz glass in 3" tape 3 feet long would be 2.25 oz. A 50/50 glass-to-resin ratio doubles that, so you're adding something less than 5 ozs total and 0.030 thickness if you're convinced you need a tougher, stronger lip.....and there is very little cost/hassle factor.
Or add a carbon tape layer inside and outside. 2 plies carbon and 4 plies glass would save a grand total of 1/2 oz compared to the original 6 plies glass. It would be roughly the same strength as the 9 ply glass lip and .030" thinner.
I'm not the least bit opposed if you want to incorporate the carbon tape (education and recreation, right?). For me, 5 oz and .030 thickness vs the additional cost and hassle wouldn't be worth it. The application is small, non-structural, and not dimensionally critical.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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