I'm finishing up an "84 GeeBee profile. It will weigh 15.5lbs.
I've put one Hitec 5945mg on rudder and one on the elevator tonight. A puzzling thing happened just after I hooked up the elevator (kevlar pull pull). I thought I'd put my finger under the elevator then push down on the elevator control on transmitter. In other words I was going to let the elevator control effectively lift up the back of the plane by pushing against my finger.

The kevlar string broke! It broke right where the string is thread through the hole in the 4-40 thread-rod. I must be doing something wrong. I just threaded the kevlar through the hole then tied a knot and CA'd it. I'm worried now.

Kevlar is supposed to be pretty strong isn't it?

How do I do this properly so the kevlar doesn't break in air?

What brand hardware are you using? Reason I ask, is that I've always used an "eye-bolt" type connector with kevlar...with good results. If your inserting it into a dubro style threaded rod, therein probably is your prob. Any case, it's chafing the kevlar strands...yes it is strong...tensile strength wise, and won't stretch.....but it's susceptible to wear, more so then steel I think.

Look into Sullivan brand, or Don's hobby has the best stuff,,,the coated kevlar..that's da stuff I think. Don's has pull pull kits that rival all I think...good luck..I do hope this helps.

Sounds like it may have been cut by the sharp edge of the hole. I'd try to figue out a way to attach it so the kevlar doesn't touch a sharp edge and you don't have to use CA.

My suggestion would be to put a 4-40 clevis there, so the kevlar is attached to the smooth round clevis pin with a fisherman's "blood knot". There would be nothing to cut the fibers, and the knot develops almost 100% of the strength of the kevlar line.

I wouldn't put CA on the line. You'll lose the flexibility, and make it more likely that the kevlar will break right where the CA ends.

Roger

Use an eye-bolt. Sullivan makes them. If you are using Kev-Cord from ACP, they sell a real neat 4-40 bolt with a hole drilled lengthwise through it. You tie a knot and pull it tight. Never had a problem with these.

Craig.

Do you ever put crimp fittings in Kevlar? That is what Don has in his kit with the coated kevlar cord?

Mark

the problem with Kevlar is.... if it touches anything...the vibration will eventually allow it to break there. use plastic coated thin stainless-steal fishing leader available at a fishing tackle store.

I am running a kevlar line with NO protection tube... ill let you know how it holds up, for now, I just keep a real good eye on it

If what Don sells is the ACP setup (Kev-Cord) then these are NOT crimp fittings. There is a wide end and a narrow end. Feed the cord through the narrow end, out the wide end, around the eye-bolt/clevis/whatever and then back through the wide end and exit the narrow end. Tie a knot. It cannot pull back through the narrow end. Do NOT crimp.

Craig.

Kev-Cord with the 4-40 bolt from ACP on my CA Extra. Rudder end:


Craig.

Crash,

Don has a crimp system with aluminum. Where do you get ACP fittings?

Mark

http://www.acp-composites.com/acp-cord.htm

What you want is .038 Kev-Cord and the Kev-Cord Connector. Even though they describe the supplied items as crimps, don't crimp them, there is no need if you use them as I described. The connectors are what is shown in the photo. I use the crimp thingys at the servo end and the bolts at the rudder end.

Craig.

Crash, I can't really see how that is secured in the photo. Could you do a more close-up pic?
Thanks.

Crash,

I have the coated Kevlar form Don's. I think its larger than .038. Any suggestions? I know the connectors form Nelson have too small of a hole.

Thanks, Mark

Check here Kevlar how I setup not to cut the Kevlar. Just go down the page. I use this type of setup on my 33% on rudder and this is its 3rd season without any problems.

Mark, You hit the nail on the head. Don's kevlar is a heavy coated cable that is just fine to crimp. I put a picture of Don's next to a 4-40 dubro. I have also used the kev-cord connecters as shown in previous pictures. I even used them on tail bracing and they work fine. I think the reason I like Don's the best is because it is a kevlar strand that has a braded coating that stands up to crimping, knotting and scraping that would easly cut other kevalar fibers.

Wings,

Thanks alot. This was the information I was looking for. Don carrries a good product, and just wanted to be sure I am using the best method of attachment.

Thanks, Mark

I would not crimp Kevlar. If you don't use a bolt, use an eye-hook and simply knot the kevlar and apply a drop of thin CA. The vinyl jacket sticks with the CA and will not come loose.

Craig.

Through Bolt: Someone asked how the kevlar was attached:

You thread the kevlar through the center of the bolt and tie a knot. The knot is pulled tight against the end of the bolt (that's why you cannot see it). The knot cannot pull back through the bolt. Very secure.

Craig.