The stiffness goes up by the third power if the thickness. Double the
thickness of a plate, and it's eight times as stiff.

--
Bob (Chief Pilot, White Knuckle Airways)


" jls" wrote in message
. ..

wrote in message
...
I've seen a few homebuilts with part of the fuselage panel that are flat
aluminum that are quite wrinkly and tend to "oil can" and make noise in
various flight attitudes. I haven't seen cross breaks used to stop
this,
although it is used in duct work to stiffen flat panels. (cross breaks
are
slight bends in the metal, done diagonally from corner to corner)

Another thought to reduce this noise is to spray urethane foam on the
panels.
I know that this foam is combustable, but I figure for it to get on fire
would
mean the pilot and passenger cabin is already engulfed, so it wouldn't
really
matter.

What do you think?

thanks,
tom pettit

A stiffening bead pressed into the panel or aluminum channel or angle
riveted to the back of the panel. My old Taylorcraft has half-circle
pressed beads on the firewall to stiffen it, and I notice the old Cessna I
have the cowl off of has a flange running horizontally across the middle
of
the firewall, plus a few other neat stiffening devices. That stiffens it
for you. You can countersink the rivets for appearance's sake if you
wish.

Stiffening a panel of fiberglas is great fun: all you have to do is make
a
sandwich with foam in between, the thicker the foam the stiffer. As a
matter of fact as the thickness increases the stiffness and strength go up
at a staggering rate. There are formulas for that and not being a
mathematician I'd best not delve into the theory of beams but if you
double
the height of a beam you have increased the stiffness and strength of the
beam by exponents of the increase in height. Let Billy B. Badd explain it
to you in his most inimitable articulate way.