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Old Feb 22, 2007, 01:01 PM
Checking CG is for NERDS!
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How do you use carbon fiber strips to reinforce a wing?!

I have been trying to find new and better ways to reinforce some of my wings and I came across the CF strips that some of you guys talk about.

What puzzles me is that these strips are typically 1/4" wide and 2' long... and completely flexible!

How does a non-ridgid strip keep a wing from flexing?
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Old Feb 22, 2007, 01:23 PM
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Read this article:

AmpAviators CF Reinforcing

When you glue down the strip, it does not flex; tubes are another way to reinforce a wing.
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Old Feb 22, 2007, 01:28 PM
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I prefer to use the rods, but I guess the strips will work. What plane are you trying to reinforce? Assuming it is something like a Slow Stick, I just tape the rod (or strip) under the leadong edge of the wing. I did the same on my GWS Beaver, but put rods on the leading and trailing edges and it made a big diference in performance. I could loop the Beaver without fear of the wings folding.
Ken
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Old Feb 22, 2007, 01:47 PM
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they flex at that length but if you shorten them and then grab them they have even less flex.. but once glued down they have zero flex... the foam will rip apart long before they flex. I use foam safe CA to hold them down. I use the "bars" to reenforce the inside tail area of all my GWS birds... and use the rod type to replae the balsa sticks in the wings. I have never had a wing fold on me... and my tails can handle a hard tail landing without breaking off.
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Old Feb 22, 2007, 02:24 PM
Checking CG is for NERDS!
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Thanks, guys!

I am going to reinforce the wings on my Corsair. I want to flog the hell out of it without worrying... this might be the stuff!

Do you think it will accomodate the curves in the Corsair wing shape? That's why I ruled out the tubes from the beginning.
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Old Feb 22, 2007, 03:27 PM
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I doubt it unless you get the really thin stuff.
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Old Feb 22, 2007, 03:56 PM
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I am not sure which CF stuff you are talking about but on foamies with thick wings like EPP models you can cut a slit and use the CF ribbon inserted with the thin dimension in the vertical axis. Once it is glued in on edge the wing becomes very stiff. I have seen demos of a child literally sitting on the foam wing hanging half off a table top.
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Old Feb 22, 2007, 08:57 PM
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Keep in mind that the CF strips are strong in one direction, but not in the other. If you're trying to prevent wing flex, you want it to be oriented vertically as Mexico described. If you just glue it flat to the wing it does have some benefit, but not nearly as much as if you cut a slot and insert it vertically.
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Old Feb 23, 2007, 07:46 AM
Checking CG is for NERDS!
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Quote:
Originally Posted by Tres Wright
Keep in mind that the CF strips are strong in one direction, but not in the other. If you're trying to prevent wing flex, you want it to be oriented vertically as Mexico described. If you just glue it flat to the wing it does have some benefit, but not nearly as much as if you cut a slot and insert it vertically.
Ahh... this makes sense. I still couldn't picture how laying the strips flat would ever work...

Thanks to all for the information!! I definitely learned from this thread.
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Old Feb 23, 2007, 10:33 AM
Oh no, not again!
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Actually, laying the strips flat works fine. Carbon fiber tape is better for a complex contour like the Corsair wing. The foam itself resists compression, and the carbon tape acts as a spar cap, providing the strength in tension. If you have a strip 1/2 -1" wide, the wing becomes nearly unbreakable. My $0.02. Jeff
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Old Feb 23, 2007, 10:53 AM
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I'm sure using something like carbon tow (basically fibers arranged in a string like tow) would work well for the Corsair's gull wing. You could dig a small channel in the foam, put some epoxy resin in, stuf in the tow, then add more epoxy. The epoxy will impregnate all of the tows, and wehn dry it will be rock solid. Use a scraper or something to remove the excess epoxy.
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Old Feb 23, 2007, 11:41 AM
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I reinforce foamy wings with 2 - 1/4" carbon strips, one top and the other on the bottom, both about 1/3 back on the wing. In order to get the strength you have to pre-load the carbon by suspending the wing between two drink glasses and putting enough weght in the center to deflect or bow it about 1/4" to 3/8". Glue the top strip on, when dry flip the wing over and weight the center enough to bow the wing just past level and glue it. When dry it will be flat and you will be shocked as to the strength of the wing. The 560 canopy glue works great for gluing the carbon strips to the foam.
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Old Feb 23, 2007, 12:04 PM
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Top & Bottom:

A strip on top of the wing and a bottom strip directly under the top one gives the best result. This configuration provides maximum stiffness (resistance to flexing). When bending forces are applied to the wing, the CF strip in tension (top or bottom) strongly resists wing flex. The wing material (foam, wood, etc) simply holds the two CF strips apart. The farther apart they are, the stronger and stiffer the wing.

If you do what "joews" says, your wing will be as stiff as it possibly can. He is right about how amazing the difference can seem to be.

Joe Minton
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Old Feb 23, 2007, 01:54 PM
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Quote:
Originally Posted by jhspring
Actually, laying the strips flat works fine. Carbon fiber tape is better for a complex contour like the Corsair wing. The foam itself resists compression, and the carbon tape acts as a spar cap, providing the strength in tension. If you have a strip 1/2 -1" wide, the wing becomes nearly unbreakable. My $0.02. Jeff
As I said, it has -some- benefit. But not nearly as much as orienting the strips vertically. Below is an example of the benefit of orienting the strips properly. This is the Speedwing 400 by Acer, it is EPP with carbon fiber strips oriented vertically. The one in the pic weighs over 22 oz., yet you can hold it at the wingtip with no flex! Installing the strips is simple, you make a shallow cut with a razor blade, push the strips in and wick some thin C/A in. Obviously the C/A can't be used on EPS, but it works great on this EPP wing I have one of these wings and it has been clocked at 93 mph, and there is NO flex in it
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Old Feb 23, 2007, 02:26 PM
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I carbon fiber most of my planes. If the tube or rod won't fit the contour, I use carbon fiber tow, layed into a slot, then wetted out with 30 or better yet, 60 minute epoxy.
I have actually built a whole wing this way.
Also most of my EP foam planes, I use C/F tow and fiberglass on the leading edge of the wing, then smooth it down with wax paper. It makes sort of a "C" cap type spar and not only stiffens up the wing, but provides impact protection as well.
I had a small Combat Wing done this way and then I packing taped over it so the other guys couldn't see the C/F leading edge. My kill ratio was over 100 to 1 and usually got knocked down because of a broken prop. Here's a EP wing on a Projeti type pusher, besides the C/Fspar and the C/F fuselage, the L/Edge of the wing is C/F as well. Also I just maidened my PC-9 and I C/F towed the wing as well. Butch

http://www.rcgroups.com/forums/showt...t=projeti+type

http://www.rcgroups.com/forums/showt...54#post6945753
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