[NSRCA-discussion] Firewall Material

[rcmaster199 at aol.com]

Tim,

You can build up cross grained balsa and carbon firewalls your self. It's easy.

Aircraft ply. 1/8", will weight almost double what a carbon balsa laminate will at 5/16" thickness.

Ed Alt discussed this technique some time ago in the KFactor. We first built up his firewall shape in cross grained light balsa and installed as many hardpoints as needed for the mount...hard points are simple maple blocks (lighter) or aircrfat ply squares (heavier), maybe 3/8" square. It requires some prep as you can see.

Lamination is straightforward. I use 3K carbon cloth, 1 layer each side, and epoxy such as ProSet, West Systems or the newest discovery JGreer, which is half the cost of the others. The assembly is inserted in a vacuum bag such as a Food Saver, and closed up. I place it on a flat surface and use a 10 lb weight on it to keep it flat.The vacuum is great because, besides the fact that you get the best contact possible between the layers, it draws epoxy into the grain and really stiffens the structure. Nonteless, before insertion into the bag, I use paper towels to remove as much of the excess as practical. You can't remove too much.

I think Ed said the weight of his Integral FW was around 40 grams. I am using the same type in my new design that has a rather large FW, and is designed for a gasoline engine. I took weights of the light ply FW I removed from my fuse and the new Carbon/balsa. Original weighed around 85 grams, and new 42grams.

MattK






-----Original Message-----
From: Pascoe,Tim [Burlington] <Tim.Pascoe at ec.gc.ca>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
Sent: Thu, Jan 28, 2010 10:29 am
Subject: [NSRCA-discussion] Firewall Material



I’m working on a pair of Genesis’ for next season. In the past, most of my airplanes have been wood, and while I have some experience with composite airframes, I’m far from being an expert. I’m ready to put in the firewalls, and I’d like some suggestions as to what the best material will be for this. I’d like to keep the weight down (don’t we all), and was wondering if laminated carbon/balsa panels such as those available at the Composites Store (http://www.cstsales.com/carbon_sandwich_panel.html)  are worth it, difficult to work with, etc. Also, do panels like this require some special reinforcement where the bolts go through? Special epoxies for adhering to the fuse, etc.? Or should I just be using aircraft grade plywood?
 
Any suggestions would be great.
 
Tim Pascoe
 


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