Are you wimping out simply because it's a transient thermodynamics
problem that involves coductive, convective, and radiative heat
transfer and a little fluid dynamics?

To that I say, you're a wise man! When the experiment is easier to do
than the calculation, do the experiment! (So long as it can be done
safely, of course.)


On Dec 8, 2:10 pm, Nomen Nescio wrote:
-----BEGIN PGP SIGNED MESSAGE-----

From: "Peter R."

A question for those of you more adept at chemistry/physics than I: How
fast does the aluminum skin of the standard single engine GA aircraft take
to cool to surrounding air temperatures? For example, how long would it
take for the skin to cool from a heated hangar at 65 degrees F to outside
air at 20 degrees F?In theory................NEVER.
It will approach 20 deg but never quite get there.

Now that I've made my heat transfer professor proud...........................

The practical answer is very complex.
First question is how close is close enough (now we're in the realm
of "engineering" as opposed to "science")
21 deg? 25 deg? Below freezing?

On an infinite plate, heat transfer is analagous to Ohm's law (V=IR).
[Temp(side1) -[Temp(side2)]= [Heat flow] [plate's resistance to heat flow]

Ok, that's easy. BUT.....................
Now you bring in convective heat transfer (that' a bit more tricky), in a
dynamic system (even more tricky), in a non-uniform system (now we're
approaching engineering hell).

So what would an engineer do to get a working answer?

I'd say tape a thermometer over the surface with the most thermal
inertia (probably over the fuel tanks) and insulate the bulb from the
environment (a washcloth folded and taped over the bulb would
probably be good enough), record the time it takes for the surface to
reach an acceptable temp. Do this with full tanks to get a maximum
time.

Caveat:
Agitation of the fuel tanks will change the whole heat transfer equation.
You could get the surface to an acceptable temp., and then have it rise
above an acceptable temp when the plane is being moved.

So there's the basic scientific answer, and the basic engineering answer.

Basic piloting answer........
Observe.....apply a little intuition.......
de-ice if it's questionable.

Basic capitalist answer.......
I'll do a full heat transfer profile for you for about 100 grand.

-----BEGIN PGP SIGNATURE-----
Version: N/A

iQCVAwUBRXnTyJMoscYxZNI5AQEQ2wP/XctN74VCtK/+iD2m6NN84cygvrh9FsWf
fg0TF10kAL6AEpo5O+GQqE62vMr8oxXSkkOBZOuRTovPr6oxy3 eXoXmbwgD3/YP/
e3lBi1gXaRNlTk+Us9ZLfYvWjG5A4bWyaKkJ+6lAB9oROVBDmL uBsbzsypU/N8iU
xtukJeGadao=
=LoQz
-----END PGP SIGNATURE-----