carbon fiber tow or kevlar tow on which panel

[atjurhs]

Hey guys,

I'm in the process of building a BD wing. The center panel is already built and wrapped with kevlar tow as per Mark's direstions (well, maybe a little bit more). Anyways, I'm currently working on the mid-panels and getting close to the point where I need to wrap the mid-panel's spar. But I've realized that I don't have enough kevlar tow to wrap both the mid-panels and the tip-panels. I only have enough to wrap either the tip panels or the mid panels.

So my options are to buy more kevlar tow and wrap all the panels with kevlar tow, or to use the carbon fiber tow that I already have. I have lots of carbon fiber tow. If I opt to use the carbon fiber tow, would it be best to use it on the mid-panel or the tip panel. Here's the options:

(1) kevlar tow wrapping all the panel's spar.
(2) kevlar on the center, carbon fiber on the mid and also on the tip panels
(3) kevlar on the center, carbon fiber on the mid, kevlar on the tip panels
(4) kevlar on the center, kevlar on the mid, carbon fiber on the tip panels

What's the pros/cons of the four possible configurations? Will one be stifer than the other? Will the carbon fiber be more brittle?

Also, if I end up buying more kevlar to wrap with, I have been using kevlar tow, is the kevlars thread that CST offers just as thick/thin or should I acquire more kevlar tow? I don't want to add more height to the spar by using a thicker kevlar.

Thanks for the help?

[rdwoebke]

I used thread on my BD. I used Tow on most of my Allegro. Wish I would have used tow on the BD, I had a spar failure on the BD that could have been contributed by the use of the thread.

I'd suggest pretty much using the tow. You can acquire it quite reasonbly shipped in an envelope from little flyer.

I might suggest the thread on the tips, as the stress is the lowest at that point and it is possibly easier to keep the tips light with the thread. And, as we know light tips are very important.

The wrap does not add any stiffness to the wing, it is burst/buckle protection. My concern over the carbon is it seems carbon really likes to soak up epoxy (this can be a good thing) but on the spar wrap that could be a good way to add very undesired weight to the mids/tips.

Ryan

[John Walter]

If you need Kevlar tow, take a look at:

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

The thread is closed, but Little Flyer still has tow for sale, so just send him a PM.

[atjurhs]

Thanks guys!

So is the thickness of the thread less than that of the tow? Ryan you are right that I don't need as much out there on the tips and thinner would be better on the tips.

Also thanks for the thought/tip about soaking up epoxy extra epoxy. I don't want that.

I bought my last batch of kevlar tow from Little Flyer. I sent him a PM two or three weeks ago about getting some more, but haven't yet gotten a reply. I'll try to PM him again.

[rdwoebke]

So is the thickness of the thread less than that of the tow?

I don't know if I'd say the thickness of the thread is less than the tow, but it is probably easier to lay down. On the flip side, I think for the high stress sections thread is harder to get right.

[atjurhs]

Then the 1K kevlar thread should work just fine for the tip panels, right?

[rdwoebke]

That 1K thread is what I used on the tip pannels on my Allegro Lite (on just the tips, not mids or center) and on the entire spare on my BD (I built the BD in 2004 and that was before I had heard of little flyer).

On both my Allegro and BD I was able to be pretty close on weight on the tips, mids were just a bit over and somehow I always have center over plan. Perhaps the 1K Kevlar thread helped me keep the tips on plan? Not sure, but that could be a contributing factor. I definitely did not put the wraps terribly close together on the tips.

Ryan

[mlachow]

You really have to be careful to avoid excess epoxy when you wet out the thread. That is the easy way to add 10-30g or more to the wing.

Best to weigh things before wrapping, then when it's wrapped and wet out to check how much you have added, then attack with paper towels or something to get more epoxy out before it cures because you realize how much epoxy you just added to your panel.