Spectra v. Kevlar

[GDbot]

I am intrigued by by the Mark Drela spar system but I was wondering if Spectra fishing line can be substituted for Kevlar thread for wrapping the spar. The Honeywell website says it is stronger than Kevlar and I can get it at Wal-Mart. Does anyone know the pro and con?

[T.D.]

Getting epoxy to stick well to Spectra is rather difficult and anyway, the Drela spars should be wrapped with bias cloth not wrapped with thread...either 1.4oz. glass or lite Kevlar. I prefer glass as it is liter and easier to apply.

IMO Kevlar (thread or otherwise) doesn't add anything in this application and Spectra would be asking for trouble.


T.D.

[glidagida]

Hi Gbot

I did all the research on Kevlar thread Vs Spectra and the others about 12 months ago and Spectra came out way ahead in all the important areas, if my memory serves me correctly strength was better as was shock load and durability exposed to sunlight-hence its use as fishing line.

As I was going to use the thread on an open structure with transparent Monokote durability in sunlight was important.

I purchased 30 Kg line as it was about the same diameter as the Kevlar thread used on the Sopranos and Trio's I sell. I put carbon caps on the spars and lightly rounded the edges not to cut the Spectra with the sharp carbon edge and began wrapping [tedious] the spars of my Grand Illusion 2M in the same pattern as the Soprano. I wrapped very tightly and closely and used instant CA to bond the Spectra to the timber spars.

No problems so far after 12 months and the carbon capped spars/Spectra is bullet proof on launch. :cool:

Cheers
GG
www.rc-sailplane.com.au

[GDbot]

Thanks Mate, that is exactly what I needed to know! Just so much easier to go to my local fishing store than go on the Web sometimes and get what I need. Again, thanks for the quick reply.

[FrogChief]

Be sure to look for unwaxed Spectra, OR find a solvent which will dissolve the wax but not the fibers.

[T.D.]

"I did all the research on Kevlar thread Vs Spectra"

In the interest of making sure the original poster gets the best information available I have to say that you must have missed a lot of information during your research GG because my own experience (and the experience of many others-http://www.rcgroups.com/forums/search.php?searchid=16636217) is at odds with your post.

But aside from that, wrapping a carbon capped spar with thread adds more weight than strength, a bias 'glass wrap is the most effective option in this application.

T.D.

[lincoln]

I should think that thread wrapping would be very useful in the joiner area, where the joiner rod is trying to pry the spar caps apart.

[T.D.]

lincoln, you're correct. Kevlar thread used locally in combination with/without a bias 'glass wrap will help tame bursting loads in the joiner area.

But using thread (especially something like Spectra) to wrap an entire spar is dubious for a host of reasons.


T.D.

[GDbot]

T.D. I am looking at the Bubble Dancer etc. and I am curious what are the host of reasons why it is dubious to wrap the spar with Kevlar or Spectra.

[John Walter]

If you need Kevlar tow, send a PM to Little Flyer. Here is a thread about his tow (pun intended :D ).

The thread is closed, but I know he has lots left.

http://www.rcgroups.com/forums/showthread.php?t=587629

[Fly2High]

There are 2 of us glider guiders that work for Honeywell that were thinking of using Spectra instead of Kevlar for wings so we asked for a sample (Honeywell makes the stuff. The european equivalent is Dyneema)

Anyway, the fabric is made of just your run of the mill poylyethlylene fibers (I believe that is what the fibers of Spectra are made of - it's been a while since we did this). Anyway it took more epoxy just to wet the stuff out, if you call that wetting out. The stuff is lighter than water and floats on water!

I do not think it really sticks to epoxy well. I think what ended up happening was that we put so much epoxy that it just surrounded it.

Well, If memory serves me, the cloth pulled off the foam far too easy for our liking. This was the newer Spectra 2000 that was suppose to be UV proof. The older stufff degraded in sunlight. This is why our interest renewed.

Good luck. You may need it. There is a reason no one uses the stuff......

As for kevlar, check a kite store. They sometimes use it for stunt kite string but it may be coated.

Just succome to ordering it. I would hate for you to take the time to build a great plane and ruin it by trying to do a shortcut.

Frank

[lincoln]

It's not for shear, it's for buckling and to hold things together where the joiner is trying to pry them apart
http://groups.yahoo.com/group/Allegro-Lite/message/1214

[rdwoebke]

But using thread (especially something like Spectra) to wrap an entire spar is dubious for a host of reasons.


.

TD,

On the built up Drela designs (Allegro Lite/Bubble Dancer), he has folks wrap the spar in Kevlar. The wraps are close together. It is pretty much the only way to wrap the spar to protect it bursth wise, since the spar is rib/balsa shearweb/rib/balsa shearweb/rib/balsa shearweb kind of thing.

Of course on his bagged wing drop in spar models (Supra, Aegea) he suggests wrapping the spar in bias cloth as that adds shear strength as well as burst strength.

Ryan

[tonyestep]

Herewith a comment from Dr Dick Williamson on this topic:

"...Spectra loses considerable strength when it is heated, e.g. when applying Monokote. The strength is lost even after cooling. Spectra may creep (stretch) more over time than Kevlar..."

[T.D.]

Ryan,

I know, I've built a Bubble Dancer, but IIRC Dr. Drela has himself stated that using thread to wrap the BD spar is not optimal but is the only way to do a wrap on a BD type wing. I believe his comments are in the archive here.

I stand by what I said about wrapping a spar with thread, it doesn't add a lot of strength except for local bursting loads but if one is going to do it Spectra is probably the worst choice of thread to use.



T.D.

[podrieger]

We use Dyneema thread for the running rigging in our 1 meter IOM sail boats. It's great for that use and it does float. You can get it at Midwestmodelboats.com.

I agree that kevlar is better for our spars on sailplanes.

Phil

[jbeanelliott]

I believe the WACO Fun 2.5 Meter by Frank Weston used Spectra cloth for vacuum bagging the wings over foam and also for the fuselage. The WACO Fun was manufactured about 15 years ago. I think I read that Spectra has a problem with creep with age so that may be another reason it is not used for RC glider wings today.

-John Elliott

There are 2 of us glider guiders that work for Honeywell that were thinking of using Spectra instead of Kevlar for wings so we asked for a sample (Honeywell makes the stuff. The european equivalent is Dyneema)

Anyway, the fabric is made of just your run of the mill poylyethlylene fibers (I believe that is what the fibers of Spectra are made of - it's been a while since we did this). Anyway it took more epoxy just to wet the stuff out, if you call that wetting out. The stuff is lighter than water and floats on water!

I do not think it really sticks to epoxy well. I think what ended up happening was that we put so much epoxy that it just surrounded it.

Well, If memory serves me, the cloth pulled off the foam far too easy for our liking. This was the newer Spectra 2000 that was suppose to be UV proof. The older stufff degraded in sunlight. This is why our interest renewed.

Good luck. You may need it. There is a reason no one uses the stuff......

As for kevlar, check a kite store. They sometimes use it for stunt kite string but it may be coated.

Just succome to ordering it. I would hate for you to take the time to build a great plane and ruin it by trying to do a shortcut.

Frank