Hi All!

> rad0 wrote:
>
> >This surpises me, in hindsight of course.  I've heard that what they call
> >foam is more like concrete.

At those speeds *anything* is 'like concrete.'

On Sat, 15 Mar 2003, M. Adam Davis wrote:

> The foam is very lightweight.

In the news I've seen the word polyurethane mentioned and I'm sure
there're many kinds but probably all very similar. It's very light but
also very hard, dense and strong, meaning you can't just poke a finger
into it (or the speeds in the atmosphere would just tear it off with the
wind turbulence.) The stuff I worked with, you can snap a 1^2" thick stick
of it in two hands, maybe 3^2" over the knee, but 6^2" is quite strong.

My Dad did a little experiment with it when I was a kid. He had a piece of
aluminum honeycomb material about 1"x6"x24". Very light and flexible, the
walls of the cells were very thin. He filled the cells with polyurethane.
It became totally inflexible and powerful strong. We set it up between two
bricks and stand on it and jump and down and it didn't even flex never
mind break.

I'd also guess that the rason they don't put the insulation -inside- the
tank is because it'd require yet another sealed inner liner with
associated weight and reliability problems. The surface of the foam was
actually very fragile, could scratch plastic flakes/dust off by just
touching it, and they -can't- allow that to get into the fuel. It's clog
things, leave residue all around, and probably affect the burn mixture
(it's flammable.)

The point being that's it's very strong, but only up to a point after
which it's just dust.

> My understanding is that on humid days (aren't all days humid down
> there? ;-)  ) the foam can still become encrusted with ice in some
> spots.
>
> My own intuition tells me that sprayed on foam, even carefully applied,
> may not always stick properly or prevent ice buildup from moisture.

Good point. So if the adhesion is a little down and the frost/ice is a
little up then parameters could easily be outside design safety limits.
Gee, can anyone spell o-ring? :/

Ice or foam though doesn't matter much because if whatever fell off the
tank hit the wing it'd do more or less the same damage. The surface of
those black tiles can be scratched with a fingernail.

Have a :) day!

jb

--
jim barchuk
jb@jbarchuk.com

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