Electric windshield defroster

[Paul Lee]

Anybody try one of those automotive rear window electric grid element defroster
kits for defrosting a portion of aircraft winshield?

[Corky Scott]

On 1 Sep 2004 21:34:11 -0700, (Paul Lee) wrote:

>Anybody try one of those automotive rear window electric grid element defroster
>kits for defrosting a portion of aircraft winshield?

The DeHaviland DH 125 (Bus Jet during the mid sixties) my father used
to fly had a sheet of gold sandwiched between two panels of safety
glass for windshield defrosting. The gold was extremely thin, as you
might assume, so that it merely tinted the windshield.

Power was routed to the terminals connected to the gold sheet and the
entire windshield heated up.

Corky Scott

[Dick Kurtz]

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. Of course the
best information would come from buying one and testing it out on some
acrylic to see if it affects it in an undesirable manner.....



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

[Robert Bonomi]

In article >,
Dick Kurtz > wrote:
>
(Paul Lee) wrote in message
>...
>> Anybody try one of those automotive rear window electric grid element
>defroster
>> kits for defrosting a portion of aircraft winshield?
>
>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.

[[email protected]]

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

>In article >,
>Dick Kurtz > wrote:
>>
(Paul Lee) wrote in message
>...
>>> 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.
>

[Capt.Doug]

>"Paul Lee" wrote in message > Anybody try one of those automotive rear
>window electric grid element defroster
> kits for defrosting a portion of aircraft winshield?

Production heated windshields in aircraft have thermistors to prevent
overheating, acrylic or glass. Your idea is valid if you can control the
temperature.

D.

[Barnyard BOb -]

>
>Production heated windshields in aircraft have thermistors to prevent
>overheating, acrylic or glass. Your idea is valid if you can control the
>temperature.
>
>D.
++++++++++++++++++++++++++++++++++++++

I suspect the heat is controlled to a safe level
by the resistance of the heating element itself.

This type of system won't meet the needs of an icing
Lear Jet at 50,000 feet, but it is sufficient for cars...
or aircraft that have no need of high wattage termistor
designs operating @ - 40 degrees F and .8 mach.

Barnyard BOb - K.I.S.S.

[Capt.Doug]

>"Barnyard BOb -" wrote in message > This type of system won't meet the
>needs of an icing Lear Jet at 50,000 feet,

Lear's system doesn't meet the needs of a Lear, hence the bath towel in
every -20 and -30 series cockpit.

> or aircraft that have no need of high wattage termistor
> designs operating @ - 40 degrees F and .8 mach.

I seem to recall some sort of temperature control on the acrylic windshield
of the Cessna 414. I can't confirm it right now because my reference
material is stored in a mandatory curfew area.

D. (still better than shoveling snow)