Epoxy and Kevlar issues

[Williamhimka]

So I’m kinda concerned right now. Well sorta…I’m building an Ultimate Wildman and working on the booster section. I got the motor mount in place and now when I was injecting epoxy through the airframe right above the top CR, I may have gotten a bit on the 1” Kevlar harness. I do have a backup plan because I’m flying this with a 75/5120 case and I have a forged eyebolt that threads right into the fwd closure as many of you know. And I can attach that harness which is connected to the motor right to the 1” harness higher up. I do hear that most of the time epoxy or glue are very strong enemies with Kevlar or nylon and that it can lead to failure of the harness later on after a few flights.
Is it a bad thing? Tips for next build? Please let me know.
Thanks
William

 

[Williamhimka]

So I’m kinda concerned right now. Well sorta…I’m building an Ultimate Wildman and working on the booster section. I got the motor mount in place and now when I was injecting epoxy through the airframe right above the top CR, I may have gotten a bit on the 1” Kevlar harness. I do have a backup plan because I’m flying this with a 75/5120 case and I have a forged eyebolt that threads right into the fwd closure as many of you know. And I can attach that harness which is connected to the motor right to the 1” harness higher up. I do hear that most of the time epoxy or glue are very strong enemies with Kevlar or nylon and that it can lead to failure of the harness later on after a few flights.
Is it a bad thing? Tips for next build? Please let me know.
Thanks
William

Also forgot to mention, the epoxy I’m using is rocketpoxy.

 

[Steve Shannon]

Epoxy isn’t an enemy of Kevlar; it doesn’t chemically attack the material. Instead, if your cord soaks up epoxy it gets stiff. Right at the edge of the stiff area a high stress area is created as the flexible material is forced to bend around the stiffer material. It works like a sharp edge. The only shock cord I’ve ever had fail in ordinary use was in a Wildman Jr. rocket where I used the supplied Kevlar cord and the base of the cord was embedded in epoxy. It snapped right at the edge of the epoxy. Since then I look for ways to attach the shock using eye bolts or u-bolts (preferred). For the Ultimate Wildman (which is a nice kit) you have plenty of room for a mechanical fastener.
As far as your strap goes, where did you get the epoxy on it? If it’s right on the end just cut it off. If it’s in the middle try arranging your shock cord so that section is protected from tension or cut it out.

 

[Williamhimka]

Epoxy isn’t an enemy of Kevlar; it doesn’t chemically attack the material. Instead, if your cord soaks up epoxy it gets stiff. Right at the edge of the stiff area a high stress area is created as the flexible material is forced to bend around the stiffer material. It works like a sharp edge. The only shock cord I’ve ever had fail in ordinary use was in a Wildman Jr. rocket where I used the supplied Kevlar cord and the base of the cord was embedded in epoxy. It snapped right at the edge of the epoxy. Since then I look for ways to attach the shock using eye bolts or u-bolts (preferred). For the Ultimate Wildman (which is a nice kit) you have plenty of room for a mechanical fastener.
As far as your strap goes, where did you get the epoxy on it? If it’s right on the end just cut it off. If it’s in the middle try arranging your shock cord so that section is protected from tension or cut it out.

Yes. So it’s right above the knot that allows it to attach to the quick link. That quick link then attaches to the U bolt. It’s a few inches above the knot like I said and not a huge gob of it it’s just a good coating I’d say. I really can’t get to it now. I have a few ideas to cut down on the stress that area would be affected by. That might be the best plan…

 

[Steve Shannon]

If it’s that close to the quick link I would just cut it off.

 

[Williamhimka]

How do you suppose I get down in there? Being a person of my size haha I don’t know how easy this will be. Should I just have my harness connected to the eyebolt on my motor?

 

[Steve Shannon]

Let me see if I understand. You put the u-bolt way down on a centering ring that you can’t get to because the motor mount tube sticks way up above it?
If that’s the situation then you will either have to make a tool or use a different way to hook your shock cord to the u-bolt. Tying a loop in it, feeding it through the u-bolt and pulling it up and then putting the other end through the loop would work.
Or you could simply cut the motor mount down to just above the centering ring so your hands can get in there.
Edited: how did you get it in there?

 

[Barkley]

Whole high end race boats have been made of kevlar and epoxy, so your issue is rigidity in the wrong place causing unnecessary shock loading. I'll echo what Steve has said above.

 

[Williamhimka]

Let me see if I understand. You put the u-bolt way down on a centering ring that you can’t get to because the motor mount tube sticks way up above it?
If that’s the situation then you will either have to make a tool or use a different way to hook your shock cord to the u-bolt. Tying a loop in it, feeding it through the u-bolt and pulling it up and then putting the other end through the loop would work.
Or you could simply cut the motor mount down to just above the centering ring so your hands can get in there.
Edited: how did you get it in there?

No. I’ll attach images. That’s where the U bolt is. Then the quick link is attached to the U bolt. And the Kevlar is attached to the quick link. Do you understand? Just let me know if you want me to make things more clear. Sorry about that haha

 

[Steve Shannon]

No. I’ll attach images. That’s where the U bolt is. Then the quick link is attached to the U bolt. And the Kevlar is attached to the quick link. Do you understand? Just let me know if you want me to make things more clear. Sorry about that haha

How do you suppose I get down in there? Being a person of my size haha I don’t know how easy this will be. Should I just have my harness connected to the eyebolt on my motor?

So I’m confused about your question about how you get down in there. Your question made me think that you couldn’t reach the quick link to unscrew it.

 

[Williamhimka]

So I’m confused about your question about how you get down in there. Your question made me think that you couldn’t reach the quick link to unscrew it.

Ahhh. Ok so yeah there’s a slight issue with that aswell. The quick link of course had to get epoxy on it as well so that’s kinda glued shut. The only way I could get to the quick link now if I were to do anything would be to shove my arm way up the motor mount tube and then I could reach it. I’m gonna see what I can do. It is so big I could probably get in there and undo the quick link maybe with a pair of pliers. I’ll let you know. It’ll be tricky. Before I do anything else, what would your recommendations be from here?

 

[Steve Shannon]

Ahhh. Ok so yeah there’s a slight issue with that aswell. The quick link of course had to get epoxy on it as well so that’s kinda glued shut. The only way I could get to the quick link now if I were to do anything would be to shove my arm way up the motor mount tube and then I could reach it. I’m gonna see what I can do. It is so big I could probably get in there and undo the quick link maybe with a pair of pliers. I’ll let you know. It’ll be tricky. Before I do anything else, what would your recommendations be from here?

Can you get a basin wrench or crowfoot ratchet attachment on the gate of the quick link?

 

[Williamhimka]

Can you get a basin wrench or crowfoot ratchet attachment on the gate of the quick link?

View attachment 526344

Wow I’ve never seen one of those. Who would you say has one? Ace or True value? Maybe Home Depot? Let me know. Which end could i go thru to get to the quick link? Should I go through the motor mount tube? Or just the top of the airframe? Or maybe it doesn’t matter. Please give me some tips on how to use this tool. It looks quite interesting

 

[David Schwantz]

First of all, if you cannot get to the Quick link, why is there a need for one? They are used to detach harness from u bolt. I like to sew a loop in the ends of the harness, and then like Steve said just thread it back though itself. This way also allows for removal at a later date.
If quick link is glued shut, heat may help to loosen it. That is if you can get in there.
If you are flying 75mm, there should be enough room for your arm to get in there.
I have the same set up with a 75/5120 mmt, I run the harness from the eye bolt in the forward closure up to the quick link at the point where the "Y" harness hooks up. This way I have 3 attachment points on the airframe, in case one fails. This type needs 2 u bolts in the upper CR.

 

[Williamhimka]

First of all, if you cannot get to the Quick link, why is there a need for one? They are used to detach harness from u bolt. I like to sew a loop in the ends of the harness, and then like Steve said just thread it back though itself. This way also allows for removal at a later date.
If quick link is glued shut, heat may help to loosen it. That is if you can get in there.
If you are flying 75mm, there should be enough room for your arm to get in there.
I have the same set up with a 75/5120 mmt, I run the harness from the eye bolt in the forward closure up to the quick link at the point where the "Y" harness hooks up. This way I have 3 attachment points on the airframe, in case one fails. This type needs 2 u bolts in the upper CR.

Sorry for the frustration of you all. I can get to the quick link. I’ll try that. Thanks again for all the info. I was actually thinking of a similar “Y” harness idea myself. I learned a few things from this. Thanks and sorry again for the confusion.
William

 

[David Schwantz]

No need to be sorry. We are all glad to help/ I know, I've been there before

 

[Steve Shannon]

Wow I’ve never seen one of those. Who would you say has one? Ace or True value? Maybe Home Depot? Let me know. Which end could i go thru to get to the quick link? Should I go through the motor mount tube? Or just the top of the airframe? Or maybe it doesn’t matter. Please give me some tips on how to use this tool. It looks quite interesting

I would just reach in from the top of the airframe; where the shock cord comes out.
All the places you listed have basin wrenches in the plumbing area, but I don’t know if they’ll fit. You bend the head over and turn the tee handle.
I try to set up my u-bolts so I can reach the quick link with my hands to unscrew it because stuff happens sometimes and the shock cord needs to be replaceable. It’s difficult sometimes I realize.

 

[Onebadhawk]

Yeah,
You guys are right..
"Y" attachment points are a good idea...
I make these for folks when I make a harness set for them..

Teddy

 

[Ronz Rocketz]

Just spitballing here. Could he attach a secondary line from the ubolt to above epoxy so if it does break at the epoxy then there's a backup?

 

[David Schwantz]

Yes he could. But I would remove the cord and get rid of the epoxy.

 

[Williamhimka]

Once again, another great idea. I’m gonna mess around with it tonight and see what I can do. I’ll let you all know what happens.
Thanks again

 

[jahall4]

@Williamhimka have not read the whole thread but stitching up your own harness might give you some more options. Here is how I do it, takes time, but is very satisfying, and far easier than you may think. At the end I explain the Y-bar harness which is stitched in such a way that the harness itself has redundancy. Let me know if you have any questions.

 

[OzHybrid]

@Williamhimka have not read the whole thread but stitching up your own harness might give you some more options. Here is how I do it, takes time, but is very satisfying, and far easier than you may think. At the end I explain the Y-bar harness which is stitched in such a way that the harness itself has redundancy. Let me know if you have any questions.

Just bought a speed stitcher. Thanks for the tip. Just need to not sew my hand accidentally....

 

[jahall4]

Just bought a speed stitcher. Thanks for the tip. Just need to not sew my hand accidentally....

You are welcome. After you poke that finger several times you'll be desensitized I see that you fly hybrids are you familiar with the UTK team flying hybrids?