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Old Feb 21, 2013, 05:12 AM
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FT.MYERS FL.
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Spar wrapping

Has anyone tried using spectra fishing line for wrapping spars? They make it in various sizes/ 30-80 # test.
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Old Feb 21, 2013, 05:33 AM
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UK, Coventry
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As long as it wraps nicely around the spar you can use anything. Before Kevlar thread I used ordinary cotton. I have a plan for a free flight competition glider that uses strips of covering tissue to bind the spar. What you don't want is something that is stretchy like monofilament line.
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Old Feb 21, 2013, 07:34 AM
Rcjpns
United States, FL, Pensacola
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I tried Spider wire, but CA glue would not hold it. So I still use Kevlar.
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Old Feb 21, 2013, 05:17 PM
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Wrapping

Vectran is anouther aramid fiber that works. Be aware that you will put a twist in the spar if you do your wrapping right.Periodically do an untwist to relieve the twist and wrap in a direction that will put washout in if not relieved.
Stew
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Old Feb 21, 2013, 05:48 PM
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Quote:
Originally Posted by CUMICBOY View Post
Has anyone tried using spectra fishing line for wrapping spars? They make it in various sizes/ 30-80 # test.
Yes it works very well. Go ahead.
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Old Feb 21, 2013, 06:41 PM
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Quote:
Originally Posted by stewswanson View Post
Vectran is anouther aramid fiber that works. Be aware that you will put a twist in the spar if you do your wrapping right.Periodically do an untwist to relieve the twist and wrap in a direction that will put washout in if not relieved.
Stew
I've never heard that. Not that I don't believe you, but can you explain how that happens? I'm just not understanding why that would occur.
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Old Feb 22, 2013, 02:37 PM
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Quote:
Originally Posted by CUMICBOY View Post
Has anyone tried using spectra fishing line for wrapping spars? They make it in various sizes/ 30-80 # test.
I have used Spectra line, but soon switched to Kevlar tow. If the Spectra is heated, it loses much of its strength. My concern is that heating the covering film (e.g., Monokote) will heat the Spectra too much.

I like Kevlar tow because it wraps quite flat and is easier to apply than Spectra, Kevlar thread or unwaxed dental floss (another good wrapping material).
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Old Feb 22, 2013, 03:20 PM
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For the best strength-to-weight I don't think you can beat kevlar thread. And it doesn't cost a lot.

Craig
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Old Feb 22, 2013, 03:38 PM
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Spectra is polyethylene and CA doesn't stick to polyethylene very well, as far as I know.

Also, Spectra is affected by UV unless coated.

Also, I has creep - keeps on stretching over time.

I would just order some kevlar thread from the composite store or some kevlar tow from the guys in RCG or a composites store.
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Old Feb 22, 2013, 06:17 PM
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Twist of spar

Quote:
Originally Posted by LVsoaring View Post
I've never heard that. Not that I don't believe you, but can you explain how that happens? I'm just not understanding why that would occur.
As you are wrapping and putting continuous tension on the wrapping material you
are putting a stress on the spar(twist). If you are securing your wraps periodically
with CA you are locking the distortion in.
Stew
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Old Feb 22, 2013, 06:51 PM
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Quote:
Originally Posted by stewswanson View Post
As you are wrapping and putting continuous tension on the wrapping material you
are putting a stress on the spar(twist). If you are securing your wraps periodically
with CA you are locking the distortion in.
Stew

Why wouldn't the tension on one side be cancelled out by the tension on the opposite side?


Now that I think about it, I assume any twist would (obviously) be in the direction of the wrap.

Still, I personally have never noticed this in any spars I have wrapped..... but I'll be looking closely on the next one!
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Old Feb 22, 2013, 07:33 PM
mosquito303
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Kansas
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What are you trying to fix/achieve? The top and bottom of the the spar take the tension and compression loads. The stuff between the top and bottom become shear loads. There is a transition in direction and magnitude of both with load.
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Old Feb 22, 2013, 07:39 PM
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The way I understand it, and by no means am I an engineer, the wrappings are really only helping where there is a wing joiner of some kind. Under load, the joiner tries to "pry" apart the top and bottom spar caps. Wrapping the spar in the joiner area prevents this.

Seems to me that wrapping in other areas, say the middle of a wing panel (on a built up woodie) provides little, if any added benefit, especially if the spar is built well, with the parts fitting properly and tightly.
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Old Feb 23, 2013, 06:36 AM
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Often, when a spar fails it is because the top spar has buckled. This is more likely with thin carbon flanges as opposed to thicker spruce ones. The wrapping along the spar helps prevent the spar lifting off he webbing and buckling.
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Old Feb 23, 2013, 07:22 AM
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Tulsa, OK
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Quote:
Originally Posted by LVsoaring View Post
Why wouldn't the tension on one side be cancelled out by the tension on the opposite side?


Now that I think about it, I assume any twist would (obviously) be in the direction of the wrap.

Still, I personally have never noticed this in any spars I have wrapped..... but I'll be looking closely on the next one!
I built a twist into an Allegro wing this way once and, for all practical purposes, it was PERMANENT. Unlike old school construction, I could not remove the twist.

I would recommend reversing the direction of the wrap for each rib bay.

Happy Landings,

Don
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