--> Europa-List message posted by: "Area-51" <goldsteinindustrial@gmail.com>
Chris, the firewall from memory is about 6.0mm phenolic material and the
drumming qualities are quite different to the rest of the fuselage; higher
pitched around 2000hz. If you have a dB app on your phone you can work these
out by going around tapping sharply with finger tip and noting all the areas
identified. On 181's firewall this is the forward facing footwell surfaces and
the upper vertical firewall/cabin surface. Engine vibration travels through the
entire airframe.
These surfaces can often act more like a speaker cone vibrating when excited by
another "modal" frequency impacting anywhere upon the body.
Technicals aside the DCI produced butyl mat only needs to be applied to 10% of
the entire drumming surface area to still be most effective. Other brands will
require 20% coverage due to density. It can be applied on the interior side of
the firewall.
DCI also produce a 3M adhesive polyester backed AL sheet which I have used
successfully lining automotive roof panels; it's very light weight, fire
resistant, sound and heat insulating, applied across entire panel, and looks
great when the edges are folded over to form an edge bead.
The 3M adhesive is a "once on never comes off" solution. You get one chance
only at putting on. On composites it will tear the base material layer away
from the body before it comes away from the adhered surface. So finger tip size
tacking points to align followed by soft paint roller application is required.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=511425#511425
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