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.

--
Peter

Except for integral fuel tanks, where warm fuel is in
contact with the skin, the aluminum skin will be below
freezing in a matter of less than a minute. The warm hanger
will have the airplane ice free and all the weep holes
should drain, but if there is snow falling, spray it with
glycol with a rich enough mixture to keep the surface ice
free for the expected take-off delay.

Even better, don't take-off in the blizzard, wait for the
snow to stop and the taxi and runways to be plowed.



"Peter R." > wrote in message
...
|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.
|
| --
| Peter

Jim Macklin > wrote:

Thanks, Jim.

> Even better, don't take-off in the blizzard, wait for the
> snow to stop and the taxi and runways to be plowed.

Only when accompanied by winds of about 25mph or stronger would I consider
lake effect snowfall a blizzard-like condition. There are many of these
events where the winds are not so strong as to blow snow across the runways
and taxiways at a rate where the plows at these two commercial airports (my
home and my destination airports) cannot keep up.

--
Peter

On Fri, 8 Dec 2006 10:18:23 -0500, "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.

The wings and tail will very quickly go to ambient air temperature, I
would guess in 1-2 minutes.

I keep my plane in a 55deg heated hangar, and have pulled it outside,
and departed during a few light snows. I have not yet had a problem
with the 'warm' wings melting the snow and causing ice droplets.

Unless the flakes are very wet/heavy, I doubt you really need to worry
about this scenario. Of course, if the flakes are wet/heavy, then
perhaps it is not a good day for flying anyway...

Peter R. writes:

> 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?

Nor more than a couple of minutes. Aluminum is an excellent conductor
of heat.

> 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.

If the wings are cold enough to freeze water, falling snow won't melt
on them.

I suppose that if snow fell on the wing while it was still above
freezing, it might freeze into ice as the wing cooled, but since the
wing will cool so quickly and since ice is hard to melt, I don't know
that this would be much of a problem.

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

Mxsmanic wrote:
> Peter R. writes:
>
> > 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?

On a clear night the skin temperature can go BELOW the air
temperature due to the radiation losses into space. We regularly see
that here, and it's what causes frost to form so quickly.

Dan

The NASA online icing course addressed part of this question:

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


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.
>
> --
> Peter

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.



"Peter R." > wrote in message
...
| Jim Macklin > wrote:
|
| Thanks, Jim.
|
| > Even better, don't take-off in the blizzard, wait for
the
| > snow to stop and the taxi and runways to be plowed.
|
| Only when accompanied by winds of about 25mph or stronger
would I consider
| lake effect snowfall a blizzard-like condition. There are
many of these
| events where the winds are not so strong as to blow snow
across the runways
| and taxiways at a rate where the plows at these two
commercial airports (my
| home and my destination airports) cannot keep up.
|
| --
| Peter

writes:

> On a clear night the skin temperature can go BELOW the air
> temperature due to the radiation losses into space.

The temperature of the aircraft won't drop below the temperature of
the ambient air, as long as the aircraft is dry.

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

Dan, it's not an important point, but from the physics/theromdynamics
side of the issue, the top surface of the wing is really at risk of
radiational cooling. The wing's leading edge's shape would allow
convective warming, as the warmer air in contact with the surface would
cool and flow downward.

writes:
> On a clear night the skin temperature can go BELOW the air
> temperature due to the radiation losses into space.


Tony wrote:
> Dan, it's not an important point, but from the physics/theromdynamics
> side of the issue, the top surface of the wing is really at risk of
> radiational cooling. The wing's leading edge's shape would allow
> convective warming, as the warmer air in contact with the surface would
> cool and flow downward.

And that's where we see frost forming: on top of the wings,
fuselage and stabilizer.


Mxmanic wrote:
>The temperature of the aircraft won't drop below the temperature of
>the ambient air, as long as the aircraft is dry.

You really should read the textbooks. Try this website:
http://www.islandnet.com/~see/weather/elements/frost1.htm

I quote from this article from the above site:

"Frost forms first on rock, glass, or metal surfaces that lose heat
more rapidly through radiative cooling than the surrounding air. This
is why car windshields frost over before frost forms on surrounding
vegetation. If the surface on which it forms has a temperature below
the frost point, frost may even appear when the officially reported air
temperature is above freezing."

The aviation weather textbooks teach the same thing. Another website,
this time by NASA:

http://aircrafticing.grc.nasa.gov/courses/ground_icing/related/4_2_1a_RI.html

Now try to tell people the dry surface temp won't drop below the
air temp.

Dan

Mxsmanic opined

writes:

>> On a clear night the skin temperature can go BELOW the air
>> temperature due to the radiation losses into space.

>The temperature of the aircraft won't drop below the temperature of
>the ambient air, as long as the aircraft is dry.

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

A clear night sky is /cold./


-ash
Cthulhu in 2005!
Why wait for nature?

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-----
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>
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> xtukJeGadao=
> =LoQz
> -----END PGP SIGNATURE-----

wrote:
> writes:
> > On a clear night the skin temperature can go BELOW the air
> > temperature due to the radiation losses into space.
>
>
> Tony wrote:
> > Dan, it's not an important point, but from the physics/theromdynamics
> > side of the issue, the top surface of the wing is really at risk of
> > radiational cooling. The wing's leading edge's shape would allow
> > convective warming, as the warmer air in contact with the surface would
> > cool and flow downward.
>
> And that's where we see frost forming: on top of the wings,
> fuselage and stabilizer.

Yea, same here. Often we'll get lots of frost on the top of the plane,
almost never on the bottom. I wasn't sure if the difference was temp or
moisture.

-Robert

writes:

> You really should read the textbooks.

I have.

> Try this website:
> http://www.islandnet.com/~see/weather/elements/frost1.htm
>
> I quote from this article from the above site:

The above site is not a textbook.

> "Frost forms first on rock, glass, or metal surfaces that lose heat
> more rapidly through radiative cooling than the surrounding air. This
> is why car windshields frost over before frost forms on surrounding
> vegetation. If the surface on which it forms has a temperature below
> the frost point, frost may even appear when the officially reported air
> temperature is above freezing."

Surfaces such as metal and glass cool more during the night because of
radiative cooling. However, they emit in the infrared, and water
vapor, CO2, and other gases in the atmosphere absorb it, so it doesn't
get very far.

Early in the morning, as temperatures rise, the air may be filled with
moisture but slightly warmer than surfaces that have cooled greatly
during the night and conduct heat well (such as metal). The moisture
in the air may condense (and even freeze) on such surfaces. But there
isn't much radiation loss at ground level unless the air temperature
is lower than surface temperatures. Remember that not only does the
atmosphere absorb infrared, but it also emits it.

> The aviation weather textbooks teach the same thing. Another website,
> this time by NASA:
>
> http://aircrafticing.grc.nasa.gov/courses/ground_icing/related/4_2_1a_RI.html

This site requires Flash, so I can't read it.

> Now try to tell people the dry surface temp won't drop below the
> air temp.

I already have.

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

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.

> 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.

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

In article >,
says...
> 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.

Put some fuel in them wings for the night. Take a while to bring all
that lot down to freezing level when you head out.

Indeed the reverse happenned to me a couple years ago, I was down in
Omarama in winter and stayed the night. Had to scrape the ice of the
wings in the morn, but they kept freezing up even though it was a lovely
sunny morning. Had to leave it for a couple of cups of coffee and let
the wing warm a bit (and all the fuel in the wing) before I was happy to
fly.

--
Duncan

You'll notice some have claimed to observe frost forming as I had
suggested it might, When theory and observations differ, it's the
theory that should change.



On Dec 8, 7:47 pm, Mxsmanic > wrote:
> writes:
> > You really should read the textbooks.I have.
>
> > Try this website:
> >http://www.islandnet.com/~see/weather/elements/frost1.htm
>
> > I quote from this article from the above site:The above site is not a textbook.
>
> > "Frost forms first on rock, glass, or metal surfaces that lose heat
> > more rapidly through radiative cooling than the surrounding air. This
> > is why car windshields frost over before frost forms on surrounding
> > vegetation. If the surface on which it forms has a temperature below
> > the frost point, frost may even appear when the officially reported air
> > temperature is above freezing."Surfaces such as metal and glass cool more during the night because of
> radiative cooling. However, they emit in the infrared, and water
> vapor, CO2, and other gases in the atmosphere absorb it, so it doesn't
> get very far.
>
> Early in the morning, as temperatures rise, the air may be filled with
> moisture but slightly warmer than surfaces that have cooled greatly
> during the night and conduct heat well (such as metal). The moisture
> in the air may condense (and even freeze) on such surfaces. But there
> isn't much radiation loss at ground level unless the air temperature
> is lower than surface temperatures. Remember that not only does the
> atmosphere absorb infrared, but it also emits it.
>
> > The aviation weather textbooks teach the same thing. Another website,
> > this time by NASA:
>
> >http://aircrafticing.grc.nasa.gov/courses/ground_icing/related/4_2_1a...This site requires Flash, so I can't read it.
>
> > Now try to tell people the dry surface temp won't drop below the
> > air temp.I already have.
>
> --
> Transpose mxsmanic and gmail to reach me by e-mail.

> Yea, same here. Often we'll get lots of frost on the top of the plane,
> almost never on the bottom. I wasn't sure if the difference was temp or
> moisture.

The bottom is subject to radiation heating from the pavement.

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 in message
. net...
>> Yea, same here. Often we'll get lots of frost on the top of the plane,
>> almost never on the bottom. I wasn't sure if the difference was temp or
>> moisture.
>
> The bottom is subject to radiation heating from the pavement.
>
> Jose

Zactly - radiation depends on what the surface is exposed to. I park my
mini-van next to a big pine tree in the driveway - the tree side is clear in
the morning- it "see's" the tree. The other windows are frosted over (even
if the overnight low is still a bit above freezing) - they are exposed to
the sky. It's a real problem with telescopes too. Since they are pointed
directly at the sky (on clear nights) the objective lens cools off rapidly
and will fog up. Look up "telescope heater".

The earth surfaces cool first through radiation, which, in turn, cools the
air (which is reasonably "transparent" to a lot of wavelengths). That's what
makes clear nights colder than cloudy nights - more heat loss to space via
radiation. And having the air cooled by the surface of the earth is what
causes surface winds to often die down at sundown - you get a layer of cold,
heavy, air that just sits there under the warmer air that is moving around
the high and low pressure areas.

During the daytime, of course, radiation from the sun warms the surface,
which then warms the air. The nice thing about that is that it is the
mechinism that triggers the thermals that keep glider pilots aloft (dragging
it back to aviation content, eh?).

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?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

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

On 8 Dec 2006 18:39:30 -0500, "Ash Wyllie" > wrote:

> Mxsmanic opined
>
> writes:
>
> >> On a clear night the skin temperature can go BELOW the air
> >> temperature due to the radiation losses into space.
>
> >The temperature of the aircraft won't drop below the temperature of
> >the ambient air, as long as the aircraft is dry.
>
> Actually, it can. I have seen frost on metal surfaces (like wings) when the air
> temp is above freezing. Taxiing will sometimes melt frost.

As usual, mxsmanic is both right and wrong (as in 'a little knowledge can be
a dfangerous thing"). When the skin radiates, it cools down, and will cool
the air in contact with its surface. This creates a thin inversion layer,
which (in the absence of any appreciable wind) is stable. The air
temperateure a few millimeters above the skin will be significantly warmer.

>
> A clear night sky is /cold./
>
>
> -ash
> Cthulhu in 2005!
> Why wait for nature?
>

Ash Wyllie writes:

> Look up _radiational cooling_.

I'm familiar with it, and with blackbody radiation.

> Space is in the single digits absolute, and the atmosphere is pretty
> much transparent to radiation.

The atmosphere not only absorbs and reflects the blackbody radiation
emitted by most objects on the ground at ordinary temperatures, it
also emits radiation of its own (as does anything with a non-zero
absolute temperature).

> Objects will radiate energy trying to heat up interstellar space,
> and cool in the process.

The surface of the planet is not part of interstellar space.

Everything on the surface of the Earth cools through emission of
radiation, but aircraft do not do this to any greater extent than
anything else, and they don't cool to subfreezing temperatures in air
that is above freezing.

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

"Ash Wyllie" > wrote in message
...

> 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.

Ash, I'd like to expand a bit on your statements.
In the 3-5 and 8-12 micrometer region of the electromagnetic spectrum,
atmospheric transmission is, like you said, close to 100% transparent. Outer
space, in those bands, is to photons like a Hoover is to dust in the
carpet - it just sucks heat right out.
The rate at which the transfer of photons occurs is dependent on, among
other things, the emmissivity of the surface and the thermal conductivity
from the mass to that surface. The perfect case is a gaussian emmissivity of
one, and since perfection is difficult, the closest you can come is a bunch
of nines behind the decimal point. A pure white specular surface is at the
opposite end of the scale.
One good example to back up your statement is in the winter time. We
have all felt the phenomena when the sky is clear that the nights are much
colder than when the sky is overcast. That is because interstellar space is
sucking the heat off the planet's surface. The adjacent atmosphere loses a
lot of its energy to the surface and its temperature decreases also.
Please, don't confuse the cloud cover effect with the so-called
"greenhouse" effect.
I always used the term "radiative cooling" (not radiational) to keep in
tune with NASA's glossary:
(http://eobglossary.gsfc.nasa.gov/Library/glossary.php3?mode=alpha&seg=q&segend=s)
radiative cooling Cooling process of the Earth's surface and adjacent
air, which occurs when infrared (heat) energy radiates from the surface of
the Earth upward through the atmosphere into space. Air near the surface
transfers its thermal energy to the nearby ground through conduction, so
that radiative cooling lowers the temperature of both the surface and the
lowest part of the atmosphere.

Oh, did I mention that I spent the better part of two decades doing infrared
measurements using a Michelson Interferometric Spectrometer? [Don't try
saying that with more than two drinks under your belt.] A lot of that dealt
with radiative transfer.

"Ash Wyllie" > wrote
>
> 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.

Why on earth are you arguing with this BoZo? He doesn't know **** from shinola,
and has proven it on many occasions and many subjects, yet still he argues with
people that do know, and then tells them that they are not qualified to make
statements on xyz subject.

You only contribute to him overstaying his welcome even longer!
--
Jim in NC

Morgans opined

>"Ash Wyllie" > wrote
>>
>> 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.

>Why on earth are you arguing with this BoZo? He doesn't know **** from
>shinola, and has proven it on many occasions and many subjects, yet still he
>argues with people that do know, and then tells them that they are not
>qualified to make statements on xyz subject.

I've quit doing so here. Mx is impervious to experience, and science.

>You only contribute to him overstaying his welcome even longer!


-ash
Cthulhu in 2005!
Why wait for nature?

"Peter R." > wrote in message
...
>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.
>
> --

You might be better off to taxi out with 20 degree wings that will not have
the snow melt and attach.

Danny


> Peter

Danny Dot writes:

> You might be better off to taxi out with 20 degree wings that will not have
> the snow melt and attach.

The wings couldn't melt snow _and_ freeze it. They could freeze water
droplets, or melt ice particles, but not both.

--
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The snow would most likely melt over the fuel tanks (if it's a wet
skinned tank) then flow aft and freeze again. I don't remember ever
having the problem, but the only time our Mooney saw the inside of a
heated hanger was when it needed to have snow and ice melted from it.
At least once I climbed aboard after it was hanger heat soaked then
took off in fairly light snow (vis at least a half mile.) I wasn't
smart enough to worry about snow melting and refreezing -- my concern
was braking, or lack of it! It couldn't have been too bad though, the
airplane didn't move during run up.

I think even with warm fuel tanks, the convective cooling would pretty
quickly get the wing surfaces cool enough to keep the white stuff
solid.





On Dec 10, 5:28 pm, "Danny Dot" > wrote:
> "Peter R." > wrote in ...
>
> >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.
>
> > --You might be better off to taxi out with 20 degree wings that will not have
> the snow melt and attach.
>
> Danny
>
>
>
> > Peter- Hide quoted text -- Show quoted text -

"Ash Wyllie" > wrote
>
> I've quit doing so here. Mx is impervious to experience, and science.

Great! Another one leaves the "Dark Side" of the force! <g>

You will feel better, if you don't fight with him, I think.
--
Jim in NC

Mxsmanic wrote:
> Peter R. writes:
>
>> 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?
>
> Nor more than a couple of minutes. Aluminum is an excellent conductor
> of heat.
>

How well aluminum conducts heat has nothing to do with it. It is all
matter of thermal mass and surface area to mass ratio. The good heat
conductivity or aluminum means that once the outside of the plane has
cooled off, the inside will cool off fast too.

--
Chris W
KE5GIX

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Mxsmanic wrote:
> Danny Dot writes:
>
> > You might be better off to taxi out with 20 degree wings that will not have
> > the snow melt and attach.
>
> The wings couldn't melt snow _and_ freeze it. They could freeze water
> droplets, or melt ice particles, but not both.

Have you tried this with your simulator?

We have six airplanes here, and when we take them out of a warm
hangar into falling snow, the snow melts on the airplane, and then the
resultant water freezes as the structure cools off. Makes a mess. Works
better to open the hangar door and let the airplanes cool off first
before moving them outside.
Maybe you should take your computer outside in various weather
conditions and see frost form or snow melt and refreeze. Be sure it's
turned off, like the real airplane.

I bet you've never seen ice fog generated by an airplane
propeller. An aircraft on runup can trugger fog over the whole airport
in a minute or two under the right conditions. Maybe the fan on your
computer could be made to duplicate it?

Dan

Chris W writes:

> How well aluminum conducts heat has nothing to do with it.

It has a great deal to do with it, because it determines how much heat
energy must be removed or added in order to reach a given temperature
at a given point. Since aluminum conducts heat well, as soon as the
skin of the plane cools, heat from within will flow into the skin and
further cooling will occur, and just about everything made of aluminum
will become cold very quickly.

If the skin were Styrofoam, it would cool almost instantly at the very
surface, but the remaining mass of foam and whatever was behind it
would stay warm much longer.

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writes:

> Have you tried this with your simulator?

No. It depends on well-known principles of physics that I don't have
to simulate.

> We have six airplanes here, and when we take them out of a warm
> hangar into falling snow, the snow melts on the airplane, and then the
> resultant water freezes as the structure cools off. Makes a mess. Works
> better to open the hangar door and let the airplanes cool off first
> before moving them outside.

That's what I would have suggested.

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Mxsmanic wrote:
> Chris W writes:
>
> > How well aluminum conducts heat has nothing to do with it.
>
> It has a great deal to do with it, because it determines how much heat
> energy must be removed or added in order to reach a given temperature
> at a given point. Since aluminum conducts heat well, as soon as the
> skin of the plane cools, heat from within will flow into the skin and
> further cooling will occur, and just about everything made of aluminum
> will become cold very quickly.
>
> If the skin were Styrofoam, it would cool almost instantly at the very
> surface, but the remaining mass of foam and whatever was behind it
> would stay warm much longer.

Sure. But it's the surface that ice forms upon, not the warmer
interior. A composite skin might cool off faster since it's insulated
from the rest of the structure.

Dan

writes:

> Sure. But it's the surface that ice forms upon, not the warmer
> interior. A composite skin might cool off faster since it's insulated
> from the rest of the structure.

Yes, but this might not be the source of most problems.

Consider an aircraft that has been soaking in the cold for a long
time. If it's built of highly heat-conductive materials, it could
easily freeze any rain falling upon the wings when it is moved
outside. I recall at least one commercial jet that may have been
brought down by this effect, but I don't remember the details.

If the wings contain fuel (which has a high specific heat and thus can
store a lot of heat or cold) and highly conductive wings, it could
freeze water at ambient temperatures well above freezing after being
cold soaked, and develop a substantial layer of ice in no time.

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