On Fri, 03 Sep 2004 01:02:47 +0000,
(Robert Bonomi) wrote:

In article ,
Dick Kurtz wrote:

(Paul Lee) wrote in message
e.com...
Anybody try one of those automotive rear window electric grid element
defroster
kits for defrosting a portion of aircraft winshield?

You could always use the electric defroster units that used to be
available back in the days of the Model "A" Ford.
They mounted to the windscreen with suction cups, about half an inch
from the glass, and warmed the glass radiantly. You would still need
to make sure the Acrylic did not get too warm.

After molding my own windsheilds recently, I can't think that these
would be a good idea. Acrylic softens at below 300 degrees F and I
think those elements get pretty close to this (locally) I imagine it
could potentially cause localized areas of melt/stress.
[[.. munch ..]]

Obviously the temperature rise depends on how much current you let flow
through the element, _and_ how fast the heat is dissipated. grin

The initial temperature also affects things.

_Without_ running any actual numbers, I suspect that the thermal resistance
of the acrylic is such that, to get enough heat over the area between
strands of the element, and considering the potential cooling effects from
the airstream, that the element temperature _would_ have to rise to the
point of adversely affecting the local strength of the acrylic.

If you're talking about using it strictly on the ground, _pre_-flight,
then it is mostly a question of 'how long are you willing to wait' for
it to have the desired effect. For some reason, if it takes 3 hours to
clear the windshield (arbitrarily pulling a number out of thin air), I
don't think it would be regarded as at all "useful", even if, technically,
it did work.

Trade-off between how hot you let the element, and thus the immediate
surrounding material, get, vs. how long it takes to clear the windshield.