I'm presuming flying IFR in light snow in a Skylane RG with no deice
equipment other that the pitot heat is OK if the temp is low enough to
preclude sticking, perhaps -10c or less.

This comes up as I contemplate flying to Minneapolis early next week.

Just is case there could be other opinions though...

Doug Carter > wrote:

> I'm presuming flying IFR in light snow in a Skylane RG with no deice
> equipment other that the pitot heat is OK if the temp is low enough to
> preclude sticking, perhaps -10c or less.
>
> This comes up as I contemplate flying to Minneapolis early next week.
>
> Just is case there could be other opinions though...

I trained for my instrument rating downwind of Lake Ontario, New York
State, during the winter of '02-'03. Most of my 17 or so hours of actual
instrument conditions logged during the training were in moderate to heavy
lake effect snow in temperatures from -2 to -15 degrees C.

Other than a very light, white film on the leading edges, the snow never
stuck to the C172 in any mass to cause concern during these, or any
subsequent flights.

--
Peter







----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
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If you can see then you are ok. Even heavy wet snow isn't really a problem.
Sometimes clouds can be "embeded" in the snow and they may contain ice.

Mike
MU-2


"Doug Carter" > wrote in message
om...
> I'm presuming flying IFR in light snow in a Skylane RG with no deice
> equipment other that the pitot heat is OK if the temp is low enough to
> preclude sticking, perhaps -10c or less.
>
> This comes up as I contemplate flying to Minneapolis early next week.
>
> Just is case there could be other opinions though...

From my real life experience: your wings are not the main problem - but the
prop. I had 2 flights in where I had to go through light snow for landing
and always the prop. was "iced" (from the spinner to half of the blades
appr. - thats why the prop heating sits exactly there, if you have it ;-) -
when you get out of the airplane and see it you are scared.

If you have to go missed - I have my doubts that you will be able to get all
the power. Now add some little ice on the wings/frame, more time in light
snow, maybe even divert - I am not going to do that again.

Bernd

"Doug Carter" > wrote:
> I'm presuming flying IFR in light snow in a Skylane RG with no deice
> equipment other that the pitot heat is OK if the temp is low enough to
> preclude sticking, perhaps -10c or less.

Bernd Seitter > wrote:

> I had 2 flights in where I had to go through light snow for landing
> and always the prop. was "iced" (from the spinner to half of the blades

Were you sure that wasn't from the clouds?

--
Peter







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Bernd Seitter wrote:
> From my real life experience: your wings are not the main problem - but the
> prop. I had 2 flights in where I had to go through light snow for landing
> and always the prop. was "iced" (from the spinner to half of the blades

do you happen to remember what the temperature was?

Any ice on your prop came from flying through cloud, not snow. Snow is
already frozen and doesn't stick.

Mike
MU-2


"Bernd Seitter" > wrote in message
...
> From my real life experience: your wings are not the main problem - but
> the prop. I had 2 flights in where I had to go through light snow for
> landing and always the prop. was "iced" (from the spinner to half of the
> blades appr. - thats why the prop heating sits exactly there, if you have
> it ;-) - when you get out of the airplane and see it you are scared.
>
> If you have to go missed - I have my doubts that you will be able to get
> all the power. Now add some little ice on the wings/frame, more time in
> light snow, maybe even divert - I am not going to do that again.
>
> Bernd
>
> "Doug Carter" > wrote:
>> I'm presuming flying IFR in light snow in a Skylane RG with no deice
>> equipment other that the pitot heat is OK if the temp is low enough to
>> preclude sticking, perhaps -10c or less.
>
>

I do not remember the temperatures (but it was not too cold, maybe -5C
Celcius on the ground - the ice did not melt from the prop). The cloud
layers were thin (maybe 2000ft) - both flights happened in southern Germany
during winter time, both alreay after sunset (quite early here in winter
time ;-)

No - I am not sure if the ice came from the clouds. But then I would have
seen more ice pickup in the clouds on the wings, and this was really just
small amount, compared to the "ice block" on the prop.

I have been to similar and more heavy icing conditions, but with an
appropriate equip. aircraft. There you could see the ice pick up very
clearly on the radar-dome under the wing (C210) while flying - on the
leading edge of the wing it is difficult to see (IMHO). On the ground I
could see parts of the wings iced while the prop. was clean as it could be.

Bernd

"Mike Rapoport" > wrote :

> Any ice on your prop came from flying through cloud, not snow. Snow is
> already frozen and doesn't stick.
>
> Mike
> MU-2

Mike Rapoport wrote:

> Any ice on your prop came from flying through cloud, not snow. Snow is
> already frozen and doesn't stick.

Wet snow can stick. A snowflake that falls into warm air (above
freezing air) doesn't instantly turn to water. Parts of it may be water
while other parts are frozen. This can stick to the airframe, or,
particularly on certain Cessnas, quickly clog the air intake.

I never had trouble in the 182 below about 25F, but I quickly clogged
the air intake in heavy snow at about 32-34F once.


Matt

If it is melting then the temp is above 0Cand the water content isn't
supercooled and it won't stick. It can certainly clog the intake though.

Mike
MU-2


"Matt Whiting" > wrote in message
...
> Mike Rapoport wrote:
>
>> Any ice on your prop came from flying through cloud, not snow. Snow is
>> already frozen and doesn't stick.
>
> Wet snow can stick. A snowflake that falls into warm air (above freezing
> air) doesn't instantly turn to water. Parts of it may be water while
> other parts are frozen. This can stick to the airframe, or, particularly
> on certain Cessnas, quickly clog the air intake.
>
> I never had trouble in the 182 below about 25F, but I quickly clogged the
> air intake in heavy snow at about 32-34F once.
>
>
> Matt

Mike Rapoport wrote:

> If it is melting then the temp is above 0Cand the water content isn't
> supercooled and it won't stick. It can certainly clog the intake though.

Well, it CAN stick as I've collected it a number of times on 172 and 182
airplanes. I can't explain for certainty why, but I'm guessing it is
the combination of water and ice crystals in the same snowflake that mix
and stick upon impact.

You don't fly much in PA in the winter without encountering snow of all
forms (and there are many forms of snow). Most doesn't stick, but some
does if the conditions are right.

Matt

Well with four years of flying in Montana I will tell you that no
matter what type of precipitation, if the static air temperature (SAT)
is anywhere from +3 degrees celsius to -17 degrees celsius and flying
in IMC the potential for icing exists.

I fly about 800 hours a year in pistion twins certified for moderate
icing conditions. The worst icing encounter I ever got was in a heavy
snow storm, about 4" in 10 minutes. Did the boots work, yea, but did
the ice go away, nope!

Also, if flying on the lee side of mountains or over water the
potential goes up exponentionally!

If you don't have an airplane certified for icing conditions please
don't becomen a statistic and go fishing, your life and the life of
your passengers aren't worth it.

Curtis
Montana

Oh, If you do get into the ice, either move your airplane 180 degrees
immediately where there was no ice, this would constitute an emergency
in an airplane not capable of flight into known icing.

Or move the airplane up or down 4000' will guarantee exiting icing
conditions, however, in my experience moving 2000' feet will exit those
conditions.

I haven't had to declare an emergency due to ice, yet, however on
several occasions I've been in mountain wave with ice accumulation and
haven't been able to maintain altitude, however, ATC was kind and
issued a block altitude and I was able to drift up and down at my
minumum controllable airspeed. Yes this was in a twin airplane capable
for flight into known icing conditions.

Even with the slightest amount of ice you need a way to rid the ice off
the windscreen to see to land. We have a plane with alcohol windows
and I guess the alcohol wasn't fresh and contained water, so it just
made matters worse. Guess it's why we get paid the big bucks to fly!

Best of luck and be safe and smart.

Curtis

"CloudyIFR" > wrote in message =
oups.com...
>=20
>=20
> Or move the airplane up or down 4000' will guarantee exiting icing
> conditions, however, in my experience moving 2000' feet will exit =
those
> conditions.
>=20
> Curtis
>

Normally that's true, but there's no such guarantee.
I've seen weird inversions giving rain and multiple freezing levels
spanning a vertical range of 10,000 feet.

From a strictly theoretical viewpoint it is diffucult to see how snow can be
both melting (implying temp>0C) and freezing to the wing (implying temp <0C)
at the same time. NASA studies have never be able to create icing above 0C.

Mike
MU-2


"Matt Whiting" > wrote in message
...
> Mike Rapoport wrote:
>
>> If it is melting then the temp is above 0Cand the water content isn't
>> supercooled and it won't stick. It can certainly clog the intake though.
>
> Well, it CAN stick as I've collected it a number of times on 172 and 182
> airplanes. I can't explain for certainty why, but I'm guessing it is the
> combination of water and ice crystals in the same snowflake that mix and
> stick upon impact.
>
> You don't fly much in PA in the winter without encountering snow of all
> forms (and there are many forms of snow). Most doesn't stick, but some
> does if the conditions are right.
>
> Matt

Mike Rapoport wrote:
> From a strictly theoretical viewpoint it is diffucult to see how snow can be
> both melting (implying temp>0C) and freezing to the wing (implying temp <0C)
> at the same time. NASA studies have never be able to create icing above 0C.

I can't explain it, but I've seen it happen enough to know that it does.
I'll venture a guess that it is due to the fact that not all of the
snowflake is melted. So, part of the flake is still below freezing and
part is above. Mash it against the wing at 150 MPH and the energy may
well equalize fairly quickly causing freezing of what was water a moment
before. Could well be similar to the way super cooled droplets work.
They are below freezing, but still liquid. Yet the slightest impact and
they freeze instantly.


Matt

Perhaps a partly melted snowflake hits the wing or another partly
melted snowflake, and the slipstream preferentially carries off the
more energetic molecules, leaving the remainder to freeze together?

Jose
--
Money: What you need when you run out of brains.
for Email, make the obvious change in the address.

On 5 Feb 2005 06:33:10 -0800, "CloudyIFR" > wrote:

>If you don't have an airplane certified for icing conditions please
>don't becomen a statistic and go fishing


Would that be ice fishing?


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Sat, 05 Feb 2005 15:49:32 GMT, "Mike Rapoport" >
wrote:

>From a strictly theoretical viewpoint it is diffucult to see how snow can be
>both melting (implying temp>0C) and freezing to the wing (implying temp <0C)
>at the same time. NASA studies have never be able to create icing above 0C.

I think what is happening is that the wing is colder (cold soaked fuel) or
the OAT changes -- perhaps with a slight climb.

I recall departing SWF one morning when it was snowing on the ground. But
the snow was melting. At about 20' AGL, the snow that had melted onto our
wing suddenly froze, and we had these little ice bumps all over the upper
wing surface.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Ron Rosenfeld wrote:

> On 5 Feb 2005 06:33:10 -0800, "CloudyIFR" > wrote:
>
>
>>If you don't have an airplane certified for icing conditions please
>>don't becomen a statistic and go fishing
>
>
>
> Would that be ice fishing?

Probably, but I never did understand why anyone wanted to catch ice?


Matt

Matt Whiting > wrote:

> So, part of the flake is still below freezing and
> part is above.

Is that really possible?

--
Peter







----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
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----= East and West-Coast Server Farms - Total Privacy via Encryption =----

>> So, part of the flake is still below freezing and
>> part is above.
>
> Is that really possible?

Of course it is. It just doesn't represent a snowflake at
equilibrium. I don't think snowflakes that are beginning to melt, and
then get rammed by an airplane wing and blasted by hundred mile an
hour freezing cold air can be expected to be at equilibrium.

Do that to me and I will =certainly= lose my equilibrium!

Jose
--
Money: What you need when you run out of brains.
for Email, make the obvious change in the address.

Peter R. wrote:

> Matt Whiting > wrote:
>
>
>> So, part of the flake is still below freezing and
>>part is above.
>
>
> Is that really possible?
>

Sure, just as it is possible for water to be below 32F and not frozen.


Matt

It goes the other way. You would have to take quite a bit of energy out of
the partially melted snowflake to refreeze it. Snow is fully crystalized.
If it is melting than the temp has to be above freezing. It the temp is
above freezing then nothing can stick. It is impossible for snow freeze
onto an airplane above 0C SAT. The temp must be below freezing and the
stuff sticking to your wing is almost certainly supercolled water from cloud
droplets.

By the time snow is melting the energy is above that required to refreeze it
and if the temp is above 0C then the energy of the snow flake is increasing
and it continues to melt.

Mike
MU-2


"Matt Whiting" > wrote in message
...
> Mike Rapoport wrote:
>> From a strictly theoretical viewpoint it is diffucult to see how snow can
>> be both melting (implying temp>0C) and freezing to the wing (implying
>> temp <0C) at the same time. NASA studies have never be able to create
>> icing above 0C.
>
> I can't explain it, but I've seen it happen enough to know that it does.
> I'll venture a guess that it is due to the fact that not all of the
> snowflake is melted. So, part of the flake is still below freezing and
> part is above. Mash it against the wing at 150 MPH and the energy may
> well equalize fairly quickly causing freezing of what was water a moment
> before. Could well be similar to the way super cooled droplets work. They
> are below freezing, but still liquid. Yet the slightest impact and they
> freeze instantly.
>
>
> Matt

"Matt Whiting" > wrote in message
...
> Peter R. wrote:
>
>> Matt Whiting > wrote:
>>
>>
>>> So, part of the flake is still below freezing and part is above.
>>
>>
>> Is that really possible?
>
> Sure, just as it is possible for water to be below 32F and not frozen.
>
>
> Matt

No. The difference is that the snowflake is *melting*. If you cool water,
it will go below 0C before freezing but ice will *not* melt below 0C (at
normal pressures).

Mike
MU-2

> No. The difference is that the snowflake is *melting*.

Well, suppose the snowflake passed through some warmer air and then
some cooler air. It would start to melt, then start to refreeze. The
outer portion of the snowflake might be freezing while the inner part
is still melting. Then this aluminum thing whips into it at a hundred
knots, and the gentle breeze it was falling through becomes a gale.

Jose
--
Nothing is more powerful than a commercial interest.
for Email, make the obvious change in the address.

He said that the snow was melting. Anyway once crystalization is started
you don't have supercooled water. The supercooled water rapidly crystalizes
which releases heat and the temp reaches 0C.

Mike
MU-2


"Jose" > wrote in message
. com...
>> No. The difference is that the snowflake is *melting*.
>
> Well, suppose the snowflake passed through some warmer air and then some
> cooler air. It would start to melt, then start to refreeze. The outer
> portion of the snowflake might be freezing while the inner part is still
> melting. Then this aluminum thing whips into it at a hundred knots, and
> the gentle breeze it was falling through becomes a gale.
>
> Jose
> --
> Nothing is more powerful than a commercial interest.
> for Email, make the obvious change in the address.

Mike Rapoport wrote:

> It goes the other way. You would have to take quite a bit of energy out of
> the partially melted snowflake to refreeze it. Snow is fully crystalized.
> If it is melting than the temp has to be above freezing. It the temp is
> above freezing then nothing can stick. It is impossible for snow freeze
> onto an airplane above 0C SAT. The temp must be below freezing and the
> stuff sticking to your wing is almost certainly supercolled water from cloud
> droplets.

Yes, I agree and didn't say anything different. My point was it may be
possible that the frozen part of the flake could absorb enough energy
from the liquid part to partially refreeze it.

I don't agree that nothing can stick above freezing. Snow will stick to
a wet surface much easier than a dry surface. If the wing is damp from
the wet snow, it may well attract "dry" snow that is impinging.

As I said earlier, I make no claim to have an explanation for this.
I've simply observed it many times in winter in PA. You can believe it
or not, your choice.


Matt

Mike Rapoport wrote:

> "Matt Whiting" > wrote in message
> ...
>
>>Peter R. wrote:
>>
>>
>>>Matt Whiting > wrote:
>>>
>>>
>>>
>>>>So, part of the flake is still below freezing and part is above.
>>>
>>>
>>>Is that really possible?
>>
>>Sure, just as it is possible for water to be below 32F and not frozen.
>>
>>
>>Matt
>
>
> No. The difference is that the snowflake is *melting*. If you cool water,
> it will go below 0C before freezing but ice will *not* melt below 0C (at
> normal pressures).

I never said it would melt below 0C. I said it is possible that the
frozen part of the flake could absorb enough energy from the liquid part
to refreeze it.

Did you ever put ice in a glass and then add some water and have the ice
cubes bond together? Same idea. If you don't believe that ice can
extract enough energy from water to refreeze it, how do you explain this?

Keep in mind that ice doesn't have to be at 0C. The temperature of ice
can be much lower than 0C and thus it can absorb a fair bit of energy
from its surroundings before melting.


Matt

Mike Rapoport wrote:

> He said that the snow was melting. Anyway once crystalization is started
> you don't have supercooled water. The supercooled water rapidly crystalizes
> which releases heat and the temp reaches 0C.

I never said there was supercooled water in the snowflake. Read again
what I wrote. I only mentioned supercooling as an example of things
happening that aren't always intuitive. Something happens in wet snow
that causes it to occasionally stick to the airfame. This isn't
intuitive, but it happens. That was the point.


Matt

"Matt Whiting" > wrote in message
...
> Mike Rapoport wrote:
>
>> "Matt Whiting" > wrote in message
>> ...
>>
>>>Peter R. wrote:
>>>
>>>
>>>>Matt Whiting > wrote:
>>>>
>>>>
>>>>
>>>>>So, part of the flake is still below freezing and part is above.
>>>>
>>>>
>>>>Is that really possible?
>>>
>>>Sure, just as it is possible for water to be below 32F and not frozen.
>>>
>>>
>>>Matt
>>
>>
>> No. The difference is that the snowflake is *melting*. If you cool
>> water, it will go below 0C before freezing but ice will *not* melt below
>> 0C (at normal pressures).
>
> I never said it would melt below 0C. I said it is possible that the
> frozen part of the flake could absorb enough energy from the liquid part
> to refreeze it.

For this to happen the water has to be supercooled. You don't get
supercooled water from melting ice. The only way that you can get
supercooled water from melting ice is to "melt it" with pressure.

> Did you ever put ice in a glass and then add some water and have the ice
> cubes bond together? Same idea. If you don't believe that ice can
> extract enough energy from water to refreeze it, how do you explain this?

Yes, I have seen this happen but it is not the same as what you are
describing. If you take a very small-thin piece of ice and allow it to
start melting it will not then freeze to anything that is above freezing. It
works with larger chunks if ice because the core temp can be significantly
lower than the surface temp. This in not true for snow.


> Keep in mind that ice doesn't have to be at 0C. The temperature of ice
> can be much lower than 0C and thus it can absorb a fair bit of energy from
> its surroundings before melting.
>
Yes, but in the case of snow which has a lot of surface area and little
volume, the flake will not have big differences in temp from one part to
another. I don't know if you are familiar with the concept of "latent hear
of fusion" but basically to convert water at 0C to ice at 0C requires a LOT
of energy to be removed.

Mike
MU-2

"Matt Whiting" > wrote in message
...
> Mike Rapoport wrote:
>
>> It goes the other way. You would have to take quite a bit of energy out
>> of the partially melted snowflake to refreeze it. Snow is fully
>> crystalized. If it is melting than the temp has to be above freezing. It
>> the temp is above freezing then nothing can stick. It is impossible for
>> snow freeze onto an airplane above 0C SAT. The temp must be below
>> freezing and the stuff sticking to your wing is almost certainly
>> supercolled water from cloud droplets.
>
> Yes, I agree and didn't say anything different. My point was it may be
> possible that the frozen part of the flake could absorb enough energy from
> the liquid part to partially refreeze it.

The snowflake has equal temp throughout because it is so thin. The whole
flake warms to freezing and then begins to melt. At this point there is too
much energy to refreeze and more energy is being added all the time by the
>0C air. To get the flake to freeze, you would have to take a significant
amount of energy out.

> I don't agree that nothing can stick above freezing. Snow will stick to a
> wet surface much easier than a dry surface. If the wing is damp from the
> wet snow, it may well attract "dry" snow that is impinging.
>
I guess that we are using different definitions of "sticking". I don't
consider tiny bits of snow suspended in water that is flowing to the
trailing edge to be sticking. By that definition, water "sticks" to an
airplane. I think that earlier you said that the snow was sticking to the
leading edge and to do that it has to be frozen.


> As I said earlier, I make no claim to have an explanation for this. I've
> simply observed it many times in winter in PA. You can believe it or not,
> your choice.
>
I absolutely believe that you have frozen stuff on the leading edge of your
wings but it is impossible for that frozen stuff to be partially melted snow
that has refrozen in above 0C air. You have snowflakes where both the ice
portion and the water portion are at 0C. There is too much energy in the
system to allow freezing and you are continuing to add more energy all the
time.

You *are* claiming to have an explanation for the white stuff on the wings.
You are claiming that it is snow. I am asserting that if can't be snow..
To get airframe icing the there has to be supercooled water present and for
supercooled water to exist, SAT has to be below freezing. Your OAT guage
reads TAT.

Mike
MU-2

In article >,
"Mike Rapoport" > wrote:

> Your OAT guage reads TAT.

Actually, in a typical GA aircraft, your OAT gauge reads some vague
approximation of the outside temperature, plus or minus who knows what. I
wouldn't trust a typical gauge to better than a couple of degrees C.

True, it's pretty easy to calibrate (stick it in a bowl of crushed ice and
water slurry and see if it reads 0), but my guess is most GA OAT's haven't
been tested since the day they left the factory. Something to think about
if you're going to play games with being in clouds near the freezing point.

Mike Rapoport wrote:

> "Matt Whiting" > wrote in message
> ...
>
>>Mike Rapoport wrote:
>>
>>
>>>It goes the other way. You would have to take quite a bit of energy out
>>>of the partially melted snowflake to refreeze it. Snow is fully
>>>crystalized. If it is melting than the temp has to be above freezing. It
>>>the temp is above freezing then nothing can stick. It is impossible for
>>>snow freeze onto an airplane above 0C SAT. The temp must be below
>>>freezing and the stuff sticking to your wing is almost certainly
>>>supercolled water from cloud droplets.
>>
>>Yes, I agree and didn't say anything different. My point was it may be
>>possible that the frozen part of the flake could absorb enough energy from
>>the liquid part to partially refreeze it.
>
>
> The snowflake has equal temp throughout because it is so thin. The whole
> flake warms to freezing and then begins to melt. At this point there is too
> much energy to refreeze and more energy is being added all the time by the
> >0C air. To get the flake to freeze, you would have to take a significant
> amount of energy out.

Do you have any data to support this? I've seen time lapse pictures of
snowflakes both freezing and melting and it doesn't happen all at once.


>>I don't agree that nothing can stick above freezing. Snow will stick to a
>>wet surface much easier than a dry surface. If the wing is damp from the
>>wet snow, it may well attract "dry" snow that is impinging.
>>
>
> I guess that we are using different definitions of "sticking". I don't
> consider tiny bits of snow suspended in water that is flowing to the
> trailing edge to be sticking. By that definition, water "sticks" to an
> airplane. I think that earlier you said that the snow was sticking to the
> leading edge and to do that it has to be frozen.

I don't think I said anything about leading edge, even though I've seen
it stick there. I believe what I said was air intake and airframe.
I've collected wet snow on the wings struts, windshield, pitot tube and
wheel pants when flying in temps between about 26-34F (according to the
OAT - never had it calibrated so who knows how accurate it was).


>>As I said earlier, I make no claim to have an explanation for this. I've
>>simply observed it many times in winter in PA. You can believe it or not,
>>your choice.
>>
>
> I absolutely believe that you have frozen stuff on the leading edge of your
> wings but it is impossible for that frozen stuff to be partially melted snow
> that has refrozen in above 0C air. You have snowflakes where both the ice
> portion and the water portion are at 0C. There is too much energy in the
> system to allow freezing and you are continuing to add more energy all the
> time.
>
> You *are* claiming to have an explanation for the white stuff on the wings.
> You are claiming that it is snow. I am asserting that if can't be snow..
> To get airframe icing the there has to be supercooled water present and for
> supercooled water to exist, SAT has to be below freezing. Your OAT guage
> reads TAT.

I was postulating a possibility. That is a far cry from claiming a fact.

Matt

"Matt Whiting" > wrote in message
...
> Mike Rapoport wrote:
>
>> "Matt Whiting" > wrote in message
>> ...
>>
>>>Mike Rapoport wrote:
>>>
>>>
>>>>It goes the other way. You would have to take quite a bit of energy out
>>>>of the partially melted snowflake to refreeze it. Snow is fully
>>>>crystalized. If it is melting than the temp has to be above freezing.
>>>>It the temp is above freezing then nothing can stick. It is impossible
>>>>for snow freeze onto an airplane above 0C SAT. The temp must be below
>>>>freezing and the stuff sticking to your wing is almost certainly
>>>>supercolled water from cloud droplets.
>>>
>>>Yes, I agree and didn't say anything different. My point was it may be
>>>possible that the frozen part of the flake could absorb enough energy
>>>from the liquid part to partially refreeze it.
>>
>>
>> The snowflake has equal temp throughout because it is so thin. The whole
>> flake warms to freezing and then begins to melt. At this point there is
>> too much energy to refreeze and more energy is being added all the time
>> by the >0C air. To get the flake to freeze, you would have to take a
>> significant amount of energy out.
>
> Do you have any data to support this? I've seen time lapse pictures of
> snowflakes both freezing and melting and it doesn't happen all at once.
>

No I don't unfortunately and no it doesn't I agree. Think about it this
way: your thesis depends on the partially melted snowflake being at a low
enough energy level to refreeze in above 0C temps. Either the water has to
be supercooled or the ice portion has to be far enough below freezing that
it can remove the latent heat from the water portion, allowing it to freeze.
The way ice forms, and you can observe this yourself (if it is below 0C), is
that the the water cools below 0C until the first crystals form, then
crystalization takes place rapidly and the water warms to 0C as latent heat
is released, then the rest of the water eventually freezes as it loses heat
to the surroundings. Flake type snow is formed by water vapor freezing
directly to the crystal, there is no intermediate liquid state. Pellet type
snow is the same as rime ice. It forms when supercooled water droplets
collide with ice crystals. When they collide the supercooled water freezes
almost instantly. When this has happened enough times the pellet becomes
heavy enough to fall.

Going the other way, from snow to water is simpler. The snow warms as it
descends into warmer air and starts to melt. It melts slowly because it
takes a lot of heat to change ice into water. The temperature is fairly
consistant thoughout the flake becasue it is warming slowly and the crystals
comprising the flake are thin with large surface area to absorb heat
(different from the ice cubes in water). The temperature also rises fairly
slowly, probably under 3C/minute (snow doesn't fall very fast).

>
>>>I don't agree that nothing can stick above freezing. Snow will stick to
>>>a wet surface much easier than a dry surface. If the wing is damp from
>>>the wet snow, it may well attract "dry" snow that is impinging.
>>>
>>
>> I guess that we are using different definitions of "sticking". I don't
>> consider tiny bits of snow suspended in water that is flowing to the
>> trailing edge to be sticking. By that definition, water "sticks" to an
>> airplane. I think that earlier you said that the snow was sticking to
>> the leading edge and to do that it has to be frozen.
>
> I don't think I said anything about leading edge, even though I've seen it
> stick there. I believe what I said was air intake and airframe. I've
> collected wet snow on the wings struts, windshield, pitot tube and wheel
> pants when flying in temps between about 26-34F (according to the OAT -
> never had it calibrated so who knows how accurate it was).

Sorry that was Jose suggesting that the airplane was crashing into the snow
flakes. I assume that the leading edges where the point where the snow
flakes "crashed".

Given that snow does not melt at below 0C I would suggest that anything
sticking to your airplane at 26F is not melting snow, it is rime ice. Rime
ice is white and porus. You can find it on any windward surface where
clouds blow by at temps below 0C. You see a lot of it on trees and ski lift
supports, particularly near ridgelines. Also when your OAT guage reads 1C
(~34F) the real static air temp is probably below 0C unless you are
practicing slow flight.. I forget the formula, but typical light airplane
speeds will produces a 2-3C temp rise.


>
>>>As I said earlier, I make no claim to have an explanation for this. I've
>>>simply observed it many times in winter in PA. You can believe it or
>>>not, your choice.
>>>
>>
>> I absolutely believe that you have frozen stuff on the leading edge of
>> your wings but it is impossible for that frozen stuff to be partially
>> melted snow that has refrozen in above 0C air. You have snowflakes where
>> both the ice portion and the water portion are at 0C. There is too much
>> energy in the system to allow freezing and you are continuing to add more
>> energy all the time.
>>
>> You *are* claiming to have an explanation for the white stuff on the
>> wings. You are claiming that it is snow. I am asserting that if can't be
>> snow.. To get airframe icing the there has to be supercooled water
>> present and for supercooled water to exist, SAT has to be below freezing.
>> Your OAT guage reads TAT.
>
> I was postulating a possibility. That is a far cry from claiming a fact.
>

Yes, and all I am suggesting is that the explanation doesn't apprear
possible from an energy standpoint. I would suggest that a more likely
explanation is that the stuff on your airplane was rime ice formed from
supercooled water and that the static air temp was below freezing.

Mike
MU-2
> Matt

Mike Rapoport wrote:

> "Matt Whiting" > wrote in message
> ...
>
>>Mike Rapoport wrote:
>>
>>
>>>"Matt Whiting" > wrote in message
...
>>>
>>>
>>>>Mike Rapoport wrote:
>>>>
>>>>
>>>>
>>>>>It goes the other way. You would have to take quite a bit of energy out
>>>>>of the partially melted snowflake to refreeze it. Snow is fully
>>>>>crystalized. If it is melting than the temp has to be above freezing.
>>>>>It the temp is above freezing then nothing can stick. It is impossible
>>>>>for snow freeze onto an airplane above 0C SAT. The temp must be below
>>>>>freezing and the stuff sticking to your wing is almost certainly
>>>>>supercolled water from cloud droplets.
>>>>
>>>>Yes, I agree and didn't say anything different. My point was it may be
>>>>possible that the frozen part of the flake could absorb enough energy
>>>
>>>>from the liquid part to partially refreeze it.
>>>
>>>
>>>The snowflake has equal temp throughout because it is so thin. The whole
>>>flake warms to freezing and then begins to melt. At this point there is
>>>too much energy to refreeze and more energy is being added all the time
>>>by the >0C air. To get the flake to freeze, you would have to take a
>>>significant amount of energy out.
>>
>>Do you have any data to support this? I've seen time lapse pictures of
>>snowflakes both freezing and melting and it doesn't happen all at once.
>>
>
>
> No I don't unfortunately and no it doesn't I agree. Think about it this
> way: your thesis depends on the partially melted snowflake being at a low
> enough energy level to refreeze in above 0C temps. Either the water has to
> be supercooled or the ice portion has to be far enough below freezing that
> it can remove the latent heat from the water portion, allowing it to freeze.
> The way ice forms, and you can observe this yourself (if it is below 0C), is
> that the the water cools below 0C until the first crystals form, then
> crystalization takes place rapidly and the water warms to 0C as latent heat
> is released, then the rest of the water eventually freezes as it loses heat
> to the surroundings. Flake type snow is formed by water vapor freezing
> directly to the crystal, there is no intermediate liquid state. Pellet type
> snow is the same as rime ice. It forms when supercooled water droplets
> collide with ice crystals. When they collide the supercooled water freezes
> almost instantly. When this has happened enough times the pellet becomes
> heavy enough to fall.
>
> Going the other way, from snow to water is simpler. The snow warms as it
> descends into warmer air and starts to melt. It melts slowly because it
> takes a lot of heat to change ice into water. The temperature is fairly
> consistant thoughout the flake becasue it is warming slowly and the crystals
> comprising the flake are thin with large surface area to absorb heat
> (different from the ice cubes in water). The temperature also rises fairly
> slowly, probably under 3C/minute (snow doesn't fall very fast).
>
>
>>>>I don't agree that nothing can stick above freezing. Snow will stick to
>>>>a wet surface much easier than a dry surface. If the wing is damp from
>>>>the wet snow, it may well attract "dry" snow that is impinging.
>>>>
>>>
>>>I guess that we are using different definitions of "sticking". I don't
>>>consider tiny bits of snow suspended in water that is flowing to the
>>>trailing edge to be sticking. By that definition, water "sticks" to an
>>>airplane. I think that earlier you said that the snow was sticking to
>>>the leading edge and to do that it has to be frozen.
>>
>>I don't think I said anything about leading edge, even though I've seen it
>>stick there. I believe what I said was air intake and airframe. I've
>>collected wet snow on the wings struts, windshield, pitot tube and wheel
>>pants when flying in temps between about 26-34F (according to the OAT -
>>never had it calibrated so who knows how accurate it was).
>
>
> Sorry that was Jose suggesting that the airplane was crashing into the snow
> flakes. I assume that the leading edges where the point where the snow
> flakes "crashed".
>
> Given that snow does not melt at below 0C I would suggest that anything
> sticking to your airplane at 26F is not melting snow, it is rime ice. Rime
> ice is white and porus. You can find it on any windward surface where
> clouds blow by at temps below 0C. You see a lot of it on trees and ski lift
> supports, particularly near ridgelines. Also when your OAT guage reads 1C
> (~34F) the real static air temp is probably below 0C unless you are
> practicing slow flight.. I forget the formula, but typical light airplane
> speeds will produces a 2-3C temp rise.
>
>
>
>>>>As I said earlier, I make no claim to have an explanation for this. I've
>>>>simply observed it many times in winter in PA. You can believe it or
>>>>not, your choice.
>>>>
>>>
>>>I absolutely believe that you have frozen stuff on the leading edge of
>>>your wings but it is impossible for that frozen stuff to be partially
>>>melted snow that has refrozen in above 0C air. You have snowflakes where
>>>both the ice portion and the water portion are at 0C. There is too much
>>>energy in the system to allow freezing and you are continuing to add more
>>>energy all the time.
>>>
>>>You *are* claiming to have an explanation for the white stuff on the
>>>wings. You are claiming that it is snow. I am asserting that if can't be
>>>snow.. To get airframe icing the there has to be supercooled water
>>>present and for supercooled water to exist, SAT has to be below freezing.
>>>Your OAT guage reads TAT.
>>
>>I was postulating a possibility. That is a far cry from claiming a fact.
>>
>
>
> Yes, and all I am suggesting is that the explanation doesn't apprear
> possible from an energy standpoint. I would suggest that a more likely
> explanation is that the stuff on your airplane was rime ice formed from
> supercooled water and that the static air temp was below freezing.

That is possible and also the airframe may have been below freezing as
often there are fairly laminar layers of varying temperature around here
in the winter. It isn't unusual when flying over the mountains to have
the OAT vary several degrees in a fairly short period of time. And when
flying in wet snow, it may well have supercooled water droplets mixed
in, but you can't really seen them.


Matt