Icing Airmets

On 28 Jan 2004 06:46:28 -0800, (Andrew
Sarangan) wrote:


Unless your plane is certified for known icing then airmet or not any
icing potential means you can't legally fly. Arguing over moderate
versus light is academic since either is prohibitive..

But what if the airplane were certified for known ice? Would it not matter then?

Many people claim that the only function of certified deice equipment
in a small GA aircraft is to give you time to get out of that
condition. If you look at the definition of light and moderate icing,
a certified system should be able to handle them. It is also my
understanding that the level of icing encountered is more complicated
than a linear relationship to temperature so that temperatures near
freezing don't necessarily imply less accumulation than lower
temperatures.

ArtP wrote:
It is also my understanding that the level of icing encountered is
more complicated than a linear relationship to temperature so that
temperatures near freezing don't necessarily imply less accumulation
than lower temperatures.

In fact, just the opposite. The worst icing happens when it's just a
little below freezing, as super-cooled droplets freeze on contact with
the airplane. As you get much colder, 1) there's less total water in
the air, and 2) what's there will already be frozen, so it mostly
bounces off instead of sticking.

"ArtP" wrote in message
...
On 28 Jan 2004 06:46:28 -0800, (Andrew
Sarangan) wrote:


Unless your plane is certified for known icing then airmet or not any
icing potential means you can't legally fly. Arguing over moderate
versus light is academic since either is prohibitive..

But what if the airplane were certified for known ice? Would it not
matter then?

Many people claim that the only function of certified deice equipment
in a small GA aircraft is to give you time to get out of that
condition. If you look at the definition of light and moderate icing,
a certified system should be able to handle them. It is also my
understanding that the level of icing encountered is more complicated
than a linear relationship to temperature so that temperatures near
freezing don't necessarily imply less accumulation than lower
temperatures.

I see this all the time too but I don't really buy off on it. I don't hear
of known-ice piston 135 charter and freight flights not making their
destinations becasue of ice. I think that if you have a known ice airplane
and everything is in proper working order, you should be capable of flying
in 99% of icing. This doesn't mean that there won't be tense moments and
obviously having more performance is better but I don't see why any known
ice airplane isn't adequate to the job.

Mike
MU-2

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

"Doug" wrote in message
om...
This was gleaned form talking to a Phd (meteorology) instructor,
Citation, Super Cub pilot.

Water will not freeze until it is 0 C or below.
Just because it is 0 degrees or below doesn't mean water HAS to
freeze.
There is themometer error, but there are also lower pressure areas on
the wing/airframe, and due to the lower pressure, the temperature
lowers.
It is possible to get ice when your themometer reads above zero, but
it will be zero or below where the ice is.

Water to ice state transition is statistical in nature and not always
governed by group temperature.

"Roy Smith" wrote in message
...
In article ,
(Andrew Sarangan) wrote:

Carb icing is a totally different fish. What's going on inside a
carburator is liquid gasoline is evaporating and turning into vapor.
There's a phase change. It takes a huge amount of energy to effect a
phase change.

A phase change is involved in the discussion at hand, but the collapse of
water's "hydrogen bridge" makes the energy involved in a gasoline phase
change look like nothing.

"Mike Rapoport" wrote in message
ink.net...

"Bob Gardner" wrote in message
news:XKARb.132385$nt4.579289@attbi_s51...
Any time air is accelerated, as it is when passing over a small-radius
surface, its temperature drops...so it is entirely possible to accrete
ice
when the temp is above zero.
first...OAT guage, struts, lower edge of windscreen where there is a lip
rather than a flush surface, etc. That is also why tail feathers begin
to
accrete ice before the wing's leading edge does.

Bob Gardner


While small radius objects do collect ice better than larger redius
objects,
temperature drop has nothing to do with it. Small radius objects have a
higher "collection efficiency" meaning more of the droplets in their path
will impact the surface. They have a higher collection efficiency because
they don't project a "bow wave" as far in front of them as larger. You
NEED
supercooled water for airframe icing.

Not exactly. Small objects and small water lead to the best conditions,
from a statistical standpoint, for gathering ice.

In article ,
"Tarver Engineering" wrote:

"Roy Smith" wrote in message
...
In article ,
(Andrew Sarangan) wrote:

Carb icing is a totally different fish. What's going on inside a
carburator is liquid gasoline is evaporating and turning into vapor.
There's a phase change. It takes a huge amount of energy to effect a
phase change.

A phase change is involved in the discussion at hand, but the collapse of
water's "hydrogen bridge" makes the energy involved in a gasoline phase
change look like nothing.



Not sure what you mean by "hydrogen bridge". I'm certainly familiar
with hydrogen bonds, and heats of vaporization and fusion, and the
energy involved in surface tension, but not the term "hydrogen bridge".
Can you explain?