[NSRCA-discussion] Firewall Material

[J N Hiller]

Tim unless absolute lightest weight is a factor a simple balsa-ply laminate
as bob describes works very well, low cost, simple and made from readily
available material.
I first started doing this 25 years ago usually on large scale airplanes
where I wanted more rigidity and flatness than 1/4" aircraft ply offered as
well as a wider edge for gluing. I've used end grain balsa but feel it isn't
worth the trouble if end grain hard points are inserted where bolts pass
through, which requires a little prior planning. I generally use dowel
(poplar if I can find it) for hard points because it's easy to cut a round
hole through the balsa sheet core with a sharpened brass tube, although
spruce block would work as well. Internal hard points give the blind nut
points something to lock into eliminating the need for an external backer or
reinforcement. I believe the balsa sheet is actually better than an end
grain balsa core when thin surface material is used as it offers better
support against dimpling under stress. I just used slow set epoxy for
laminating, clamping the 'sandwich' between two pieces of 3/4" plywood or
weight it down on the workbench.
I don't have a paint booth so I still build wood airplanes and use iron on
paint.
Jim Hiller



-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Pascoe,Tim
[Burlington]
Sent: Thursday, January 28, 2010 7:29 AM
To: General pattern discussion
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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