Icing Airmets

Mike Rapoport wrote:
"C J Campbell" wrote in message
...

"Dave" wrote in message
hlink.net...
| I'd like to know how you get in icing when the temperature is +5. I have
| never seen ice until the the gauge reads 0 or below.

Icing occurs when liquid water freezes on an airplane surface that is

below

freezing. The aircraft may have been cooled earlier when it flew through a
layer.


Almost. Icing occurs when a below freezing aircraft encounters supercooled
water. Supercooled water does not exist above 0C.


True, but only partially correct.

Above-freezing water will still freeze and cling to your below-freezing
airframe. In fact, the preferred migration of liquid and of
not-condensed water vapour is "from warm to cold". So moisture will
migrate to the below-freezing airframe.... you can even get a thin sheet
of ice forming in absolutely clear air, simply from the condensation of
the water vapour. (similar to your glasses fogging when you come inside
from the cold)


Until such time as the airframe finally warms up to ambient and sheds
the ice.

Agreed , but my below freezing airframe's oat gauge will also read below 0.


"Icebound" wrote in message
ble.rogers.com...
Mike Rapoport wrote:
"C J Campbell" wrote in message
...

"Dave" wrote in message
hlink.net...
| I'd like to know how you get in icing when the temperature is +5. I
have
| never seen ice until the the gauge reads 0 or below.

Icing occurs when liquid water freezes on an airplane surface that is

below

freezing. The aircraft may have been cooled earlier when it flew through
a
layer.


Almost. Icing occurs when a below freezing aircraft encounters
supercooled
water. Supercooled water does not exist above 0C.


True, but only partially correct.

Above-freezing water will still freeze and cling to your below-freezing
airframe. In fact, the preferred migration of liquid and of
not-condensed water vapour is "from warm to cold". So moisture will
migrate to the below-freezing airframe.... you can even get a thin sheet
of ice forming in absolutely clear air, simply from the condensation of
the water vapour. (similar to your glasses fogging when you come inside
from the cold)


Until such time as the airframe finally warms up to ambient and sheds
the ice.

"Icebound" wrote in message
ble.rogers.com...
Mike Rapoport wrote:
"C J Campbell" wrote in message
...

"Dave" wrote in message
hlink.net...
| I'd like to know how you get in icing when the temperature is +5. I
have
| never seen ice until the the gauge reads 0 or below.

Icing occurs when liquid water freezes on an airplane surface that is

below

freezing. The aircraft may have been cooled earlier when it flew through
a
layer.


Almost. Icing occurs when a below freezing aircraft encounters
supercooled
water. Supercooled water does not exist above 0C.


True, but only partially correct.

Above-freezing water will still freeze and cling to your below-freezing
airframe. In fact, the preferred migration of liquid and of
not-condensed water vapour is "from warm to cold". So moisture will
migrate to the below-freezing airframe.... you can even get a thin sheet
of ice forming in absolutely clear air, simply from the condensation of
the water vapour. (similar to your glasses fogging when you come inside
from the cold)


Until such time as the airframe finally warms up to ambient and sheds
the ice.


Which will happen before any of the theorized freezing takes place at least
at the leading edges.

Mike
MU-2

Icebound wrote
Almost. Icing occurs when a below freezing aircraft encounters supercooled
water. Supercooled water does not exist above 0C.


True, but only partially correct.

Above-freezing water will still freeze and cling to your below-freezing
airframe.

Not at any significant rate. The issue is heat transfer. If the
water is not already at or below the freezing point, then it must shed
excess heat and be cooled to the freezing point, or it will not
freeze. Even if a droplet comes into contact with a subfreezing
surface, most of it will be long gone before it can cool sufficiently.

In fact, the preferred migration of liquid and of
not-condensed water vapour is "from warm to cold". So moisture will
migrate to the below-freezing airframe....

This makes no sense.

you can even get a thin sheet
of ice forming in absolutely clear air, simply from the condensation of
the water vapour. (similar to your glasses fogging when you come inside
from the cold)

This is true, but wholly irrelevant. The accretion rate involved is
so low as not to matter.

Michael