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Foam Filling - Printable Version

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Foam Filling - Chris Mc - 22-10-2014

Calling on the Members expertise.

I have a Dynam Waco that's ripped the undercarriage out on 3 occasions....yeah I know, learn how to land properly, blah blah.

I was wondering if there is a lightweight filler compound that can be used to strengthen the fuse and re-fix the mounting plate.

Being central to the plane hopefully will not upset COG but obviously the lighter the better.

Any thoughts?

RE: Foam Filling - secant0give - 22-10-2014

I normally use Micro light filler mixed with west systems epoxy for filling jobs. that makes a really nice light strong bog for filling things. It's not as flexible as foam tho so it will cause a hard point where it joins the foam.

or

You could always get some Hard dense EPS foam cut out the effected area and fit in a new piece using hot melt glue. that bonds really well to both EPO and EPS foam. (EPS = Expanded Polystyerene)

or

You could cut some slots and insert some 1.6mm ply some into the foam, underneath & perpindicular to the mounting plate and lengthwise along the fuse. That would toughen it up a as well. Two hacksaw blades CA'd together cut about the right width slot. Just make the pieces different lengths so they don't cause a hard point for the fuse to break right where they end.

Normal CA bonds very well to EPO foam and also to EPP foam but EPS foam hates it, Be ware Normal CA melts EPS!!

Hope this helps chris it's a bit hard to difinativly suggest something unless unless you can have close look at it but heres a couple of things to think about. Smile

You can also use polyurithane spray foam as a light filler, It's a bugger to work with and you want to do a practice piece first. I'm not sure how good it will be structurally tho' You kind of spray it on, it expands to heaps more than you want then you let it cure for a day and trim it off with a sharp knife later.

Good Luck

RE: Foam Filling - Chris Mc - 22-10-2014

Thanks mate. I like the sound of Option 3 using Ply, think would give the backing plate a solid base to adhere to.

RE: Foam Filling - symowallo - 22-10-2014

Depending on the fracture/crack, I would consider epoxy with microballoons/inorganic microspheres mixed in with it, as Jason suggested.

The more microballoons you put in, the lighter it'll be.

RE: Foam Filling - secant0give - 24-10-2014

Yes there are a couple of products you can use as a light filler mixed with epoxy

west microlight which is phenolic micro baloons, Ie bubbles made form backalight It's really light and easy to sand.

There is West microspheer blend which is a blend of glass micro baloons and I think coloidal silica, It's a little tougher and a bit heavier and still reasonable to sand

You can get Q-cell which is just glass micro baloons with nothing else.

There are a couple of very strong epoxy fillers but they make a pretty heavy bog
There's west micro fiber blend which is cotton fiber and colloidal silica It's great as an adhesive filler but heavy used a lot for boat building.

You can buy just the cotton fiber which is good to add to the micro-light filler because it gives you a light and reasonably strong filler but makes it a little harder to sand.

The good thing about epoxy is you can use a combination of fillers to suit just what you want to do.

IMPORTANT use slow set epoxy and mix the part A and part B thoroughly first before adding the filler. I like west systems epoxy with the slow hardener it has a great shelf life too

Always use gloves when mixing and working with epoxy don't get it on your skin it's nasty until it cures!! Vinal gloves are better than latex ones as well. If you use latex change them regular as the epoxy permeates latex slowly.

Good luck !!

RE: Foam Filling - symowallo - 24-10-2014

That's the one - Q-Cel. I use Q-Cel for fibreglass repairs. I have found it to be very good. It doesn't impact strength all that much - I have used it to fix jetskis from surf and impact damage over the years, so it's certainly good enough for model aircraft. It definitely keeps the weight down.

Like you said Jason - I agree, the West system is good. The Aussie ones aren't bad either.