kevlar and epoxy - RC Groups
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Feb 04, 2013, 10:33 PM
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kevlar and epoxy

I have some Kevlar tow I would like to use to strengthen a firewall. Can I use standard 30min epoxy to do this with or do I need special resins for this? The aircraft is a .40 size which I'll be adding a .60 to; so the old firewall is getting new holes drilled for a mount and stuff. The aircraft will be moving at about 120mph and I need the firewall to stand up to the new abuse of a .60.
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Feb 04, 2013, 11:37 PM
I am actually really slow
Why do you want to use Kevlar?

I would be using carbon tow instead or just some fiberglass cloth. Proper laminating resins arnt necessary but recommended.
Feb 04, 2013, 11:57 PM
Registered User
I want to use Kevlar because that's what I have on hand and I don't want to buy anything to make this aircraft work since my budget is limited.

So there "shouldn't" be any issues with using regular great planes 30min epoxy then?
Feb 05, 2013, 04:59 AM
Life begins at transition
Use heat to thin it. It'll be very thick compared to a "proper" resin, which is about the consitancy of milk.

Some use alcohol or acetone, but that affects the final strength.
Feb 05, 2013, 06:59 AM
I am actually really slow
As soon as you put heat to it your working time will go from 30 mins to 2 mins (slight sarcasm, but you will have to work alot faster)

I'm not sure how much good Kevlar would do to reinforce a firewall. It certainly wouldn't be on my list of materials if I had to 'reinforce' something. That's if I was using a good laminating resin to.

Strongly suggest going down to a local marine shop and picking up some 100g glass instead.
Feb 05, 2013, 10:42 AM
Registered User
Why wouldn't you guys use kevlar? Is it not stiff enough or something?
Feb 05, 2013, 11:11 AM
I am actually really slow
There's nothing bad about the mechanical properties of Kevlar but resin more encapsulates the kevlar fibers rather then bonding with it. I just dont think standard 30min epoxy and kevlar rovings will do you much good. You will get a stronger firewall if you just use fiberglass cloth. It would probably look neater to, kevlar is a pain to work with and things can get real messy quickly.
Feb 05, 2013, 12:15 PM
Registered User
I was going to do this on the inside of the firewall / airframe so the looks don't matter much, I just need it to work. I've read about resin encapsulating the kevlar but from my searches that only seems true with certian types of resin and my standard epoxy might be one of those. So I've been looking at West Systems epoxy resin. I figure since I will be using the kevlar to reinforce more things down the road I should just go ahead and invest in some quality resin.

Does anyone have any experience with the west systems epoxy resin and kevlar?
Feb 06, 2013, 07:57 PM
Registered User
I do not know what your firewall is made of, but seems to me if you were to
1/ apply a layer of resin on the firewall
2/ lay your kevlar tow in 2 layers perpendicular to each other to the resined firewall, remove as much of the resin excess as possible with a paper towel
3/ stick another layer of ply on top of that, effectively sandwiching your kevlar
then that would be plenty strong
thin epoxy is better as it will wet the fibres much better and you can blot the excess, but it does not look like weight is a key concern to you so your 30mns epoxy will probably do the job although it will be a bit messier to apply and work with.
ideally you would use carbon fibre for this but given you already have the kevlar I would not run buy some carbon - plenty of dlg wings are bagged with kevlar / epoxy and they do withstand a massive amount of abuse. kevlar IS a pain to cut and sand but again since it is all internal you probably won't have to make it pretty
Feb 07, 2013, 10:11 AM
Registered User
Thanks for the boost of confidence on this. However, I went to go do this last night and I guess if you don't use epoxy within a year it goes bad. My resin was rock hard and it was a fairly new bottle; I even stored it inside my home, in a temperature controlled closet.
Feb 09, 2013, 04:01 AM
Registered User
Well with tight space I had to work with I ended up cutting a bunch of 2" strips and then mixed them with a bunch of 5min epoxy. Seems to hold up well for what I needed but I will use cloth from now on because the tow is really hard to work with like this. Looks like crap but as long as it works, right? Lol At least it will be concealed in the fuel tank bay.
Feb 09, 2013, 10:00 AM
Hope to get out of life alive
kenh3497's Avatar
I've always had good luck by adding triangle stock to the fuse/firewall junction. If a little more strength is needed just some wally world glass cloth works fine to bridge over the tri stock to the fuse and firewall. A package of that is not much money and will last for several years in that application.


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