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Feb 21, 2013, 05:12 AM
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Discussion

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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Feb 21, 2013, 05:33 AM
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mhodgson's Avatar
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.
Feb 21, 2013, 07:34 AM
Rcjpns
I tried Spider wire, but CA glue would not hold it. So I still use Kevlar.
Feb 21, 2013, 05:17 PM
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stewswanson's Avatar

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
Feb 21, 2013, 05:48 PM
Chuck it and see!
Wing-span's Avatar
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.
Feb 21, 2013, 06:41 PM
It's gonna be YUGE!!!
LVsoaring's Avatar
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.
Feb 22, 2013, 02:37 PM
Registered User
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).
Feb 22, 2013, 03:20 PM
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craigrrr's Avatar
For the best strength-to-weight I don't think you can beat kevlar thread. And it doesn't cost a lot.

Craig
Feb 22, 2013, 03:38 PM
Chuck 'Em and Chase 'Em
Fly2High's Avatar
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.
Feb 22, 2013, 06:17 PM
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stewswanson's Avatar

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
Feb 22, 2013, 06:51 PM
It's gonna be YUGE!!!
LVsoaring's Avatar
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!
Feb 22, 2013, 07:33 PM
mosquito303
mosquito303's Avatar
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.
Feb 22, 2013, 07:39 PM
It's gonna be YUGE!!!
LVsoaring's Avatar
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.
Feb 23, 2013, 06:36 AM
Registered User
mhodgson's Avatar
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.
Feb 23, 2013, 07:22 AM
Flying = Falling (Slowly)
dharban's Avatar
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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