How fast does the skin of the airplane cool to surrounding temperatures?

Tony wrote:
You'll notice some have claimed to observe frost forming as I had
suggested it might,

Agreed. It's quite common for frost to form on glass and metal
surfaces that are exposed to a clear night sky even when the local air
temperature never drops below 35F at any time.

When theory and observations differ, it's the
theory that should change.

But in this case the observations are in good agreement with the theory
of radiant heat transfer to a clear night sky.

The effect is well known to amateur astronomers since it causes the
optics of their telescopes to cool down below the dew point and have
water condense on them even though the air temperature remains well
above the dew point. Various solutions are used such as slight heating
of the optical elements or installing tubes (dew caps) that extend well
past the end of the telescope and therefore don't allow as much heat
radiation to the cold, clear night sky.

Mxsmanic opined

Ash Wyllie writes:

Actually, it can. I have seen frost on metal surfaces (like wings) when the
air temp is above freezing.

What was the temperature profile of the air during the preceding
hours, and at the exact time of the observation?

If the air is warming up and moist, metal surfaces might well be below
that temperature and below the dew point.

It was before dawn, and the temp had dropped over night (and was still dropping).

A clear night sky is /cold./

Yes, because large masses of water vapor have a moderating effect on
temperature, making warm days cooler and cold days warmer.

Look up _radiational cooling_ . Space is in the single digits absolute, and
the atmosphere is pretty much transparent to radiation. Objects will radiate
energy trying to heat up interstellar space, and cool in the process.

You might drop in on some of the amatuer telescope groups. They have the same problem.


-ash
Cthulhu in 2005!
Why wait for nature?

Jim Macklin wrote:

Just remember the snow on the wing does not blow off during
take-off. Moderate snow is snow with the visibility reduced
to not less than 1/2 mile, which is low IFR.

It will if it is freshly fallen snow on a cold wing. Often, it will
blow off just taxing in the wind. I've lost half of the snow on the
wing just taxiing to the pumps. The rest is easily brushed off if it is
fairly fresh and hasn't yet seen above freezing temps.

I'm not recommending using the takeoff as a snow removal technique, but
fresh snow will blow off once a little wind gets on it. I do us this
technique often with my cars and it works great. :-)

Matt

M wrote:

The NASA online icing course addressed part of this question:

http://aircrafticing.grc.nasa.gov/courses.html

Thanks for the link.

--
Peter

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote:

But to get back to the orignial post - just ask the guy in the next hanger,
he/she ought to know if they have been in the area a few years, right?

In the several months since starting my hangar contract at that airport I
have yet to meet any of the fellow hangar lessees. Either they don't fly a
lot or my arrival/departure timing is out of sync with theirs. Most likely
the latter.

--
Peter

peter writes:

But in this case the observations are in good agreement with the theory
of radiant heat transfer to a clear night sky.

How much frost do you see condensing on Styrofoam?

--
Transpose mxsmanic and gmail to reach me by e-mail.

Peter R. wrote:
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?

This is my first winter where my airplane sits at my destination airport
(Buffalo, NY) all week in a heated hangar. The problem I just inherited
is that if I desire to depart during a lake effect snowfall event, falling
snow could melt on the wings and fuselage and then turn to ice.

Buy ($80) or borrow an infrared remote thermometer and get some data.
NB: The laser only tells where the center of the cone is. It is not
involved in the measurement at all.

"Nomen Nescio" wrote in message ...
: -----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.


Great post...thanks!

I'm not recommending using the takeoff as a snow removal technique, but fresh snow will blow off once a little wind gets on it. I do us this technique often with my cars and it works great. :-)

My experience (with watching snow blow off cars) is that it blows off
only from the very top surface, so takes quite a while to blow off
completely. Much more than a takeoff run - maybe a trip to my aunt's.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

Jose wrote:
I'm not recommending using the takeoff as a snow removal technique,
but fresh snow will blow off once a little wind gets on it. I do us
this technique often with my cars and it works great. :-)


My experience (with watching snow blow off cars) is that it blows off
only from the very top surface, so takes quite a while to blow off
completely. Much more than a takeoff run - maybe a trip to my aunt's.

Yes, it depends a lot on the type of snow, temperature and shape of the
car. Wet snow will not blow off to any significant degree. Dry snow on
a cold surface will blow off almost completely. Cars don't have good
airflow around them with a lot of stagnation points that trap snow.
Airplane wings don't have such issues and the airflow is fairly uniform
over them.

If I have dry snow on the wings, I generally taxi a ways to see how much
blows off. Then I clean off the remains by hand. Some days there is
nothing left to sweep off and some days it is all left. :-(


Matt