Thanks for bringing this over Montblack. I really wish I would have
caught my typo because I think it pulled away from my main
point/question, which is, "What is the difference in thermal
conductivity (as it relates to ice/icing conditions) between a
composite wing and an aluminum wing."

Obviously, at certain extreme temperatures and conditions (NH in
January), both an aluminum and composite wing may act similarly, or in
other words, the therrmal conductivity/icing differences may not be
distinguishable.

But in marginal temperatures and conditions, (like SC in February),
those differences MAY be quite distinguishable, as the experience I
posted, and may be a point of concern for composite drivers.

Or I may be completely bonkers. But the only logical explanation I
could reason/infer from my experience was that the thermal conductivity
differences between aluminum and fiberglass were to blame.

This probably breaches usenet protocol, but I shall reprint my original
post from r.a.student that Montblack refers to below, with the
temperature typo corrected.

"I am training in a Diamond DA-20 C1, incidentally, the only
composite airplane on my flight schools ramp. I am flying in upstate
SC. This morning, at 8:15 the top surfaces of the wings on the C1 were
iced significantly, as was the nose and fuselage (tail boom). Outside
air temp was 41*F/Overnight low was 30*F. Plane is tied-down, morning
sun was directly on wing surfaces, no intervening shadows. My lesson
was delayed, of course.

Curious, I checked the other planes on the ramp-all of which are
aluminum. NONE had icing on any surface. Through a very unscientific
"hand touch" test I determined the composite surfaces "felt" much
colder than the aluminum surfaces.

I would be very interested in learning more about the heat/cold
transfer dynamics of aluminum versus composites. Pure speculatin'
though, I would bet from my limited experience that the composite will
ice faster or retain ice longer than similarly exposed aluminum. But,
there's always someone who knows more about it than me-so maybe they
will chime in.

So, I did some research and found the following thermal
conductivity values (Note these figures are for a standard temperature
of 25*C):

Aluminum,
Pure=237 watts/meter*Kelvin

Fiberglass,
Paper Faced=.046 watts/meter*Kelvin

So, what I should have inferred from my non-aviation experience with
these materials is confirmed by the above thermal conductivity values.

That is, aluminum is a good heat conductor-it can either gain or lose
heat very quickly. Fiberglass on the other hand is a good insulator.
It does not lose or gain heat very rapidly. Thus once "set" at a
temperature, it will tend to remain there longer than aluminum.

Therefore versus fiberglass the aluminum surfaces
will cool to icing temperatures faster, and conversely will heat to
non-icing temperatures faster. The composite will cool more slowly,
but once cooled, will retain that temperature much longer, meaning like
I discovered this morning, my composite plane will/may be iced when the
Cessnas, Pipers and Mooneys won't.

During the preflight "Hand Checking Of All Surfaces" has added meaning
for a composite driver (especially one like me who has scheduled 8am
lessons so that I can at least pretend there is a usable workday
left.

WPR
Student Pilot"