flying into snow showers without deice

"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