Iced up Cirrus crashes

("greenwavepilot" wrote)

snip
Michael, I am training in a Diamond DA-20 C1, incidentally, the only
composite airplane on my flight schools ramp. I am flying in upstate
SC. This morning, at 8:15 the top surfaces of the wings on the C1 were
iced significantly, as was the nose and fuselage (tail boom). Outside
air temp was 41*F/Overnight low was 40*F. Plane is tied-down, morning
sun was directly on wing surfaces, no intervening shadows. My lesson
was delayed, of course.


There can be a thermal "dip" right before sunrise, right about at wingtip
height. Duck hunters and deer hunters will confirm (and curse) this
temperature phenomenon - forget what it's called.

41F overnight? 40F at 8:15? And still ice?

So it either go down to 32F at or near your wing, or it was below 32F a
number of feet, maybe many, many feet above your wing? Or your wing was 32F
at some point in the early morning? Wonder what it was?

Also wonder what the height of the temp reading instrument is?

Our local airport can report 40F with an overnight low of 36F yet there will
sometimes be "white-ice-dew" on the grass those mornings - usually in the
fall. We keep track of this because of our flower garden and outside plants.
Minnesota flowers in late October are a night-by-night proposition. Ooh,
there go the Impatiens.

Our airport's automated weather reporting station is less than two miles
away. Plus geologically, we are all at an identical elevation sharing the
same glacially flat sandy river bottom. This area was all sod farms just a
few years back - no other farming is sustainable in this area. Anyway, we
usually always agree with the airport temps - here at home, in the car,
neighbors thermometer, etc.

37F-40F and frost on the grass in the morning is common here.


Montblack

Montblack wrote:
("greenwavepilot" wrote)

snip

Michael, I am training in a Diamond DA-20 C1, incidentally, the only
composite airplane on my flight schools ramp. I am flying in upstate
SC. This morning, at 8:15 the top surfaces of the wings on the C1 were
iced significantly, as was the nose and fuselage (tail boom). Outside
air temp was 41*F/Overnight low was 40*F. Plane is tied-down, morning
sun was directly on wing surfaces, no intervening shadows. My lesson
was delayed, of course.

There can be a thermal "dip" right before sunrise, right about at wingtip
height. Duck hunters and deer hunters will confirm (and curse) this
temperature phenomenon - forget what it's called.

41F overnight? 40F at 8:15? And still ice?

So it either go down to 32F at or near your wing, or it was below 32F a
number of feet, maybe many, many feet above your wing? Or your wing was 32F
at some point in the early morning? Wonder what it was?

The temperature of a surface that's radiating heat to a clear night sky
can drop considerably below the ambient air temperature. So it's
possible for frost to form even when the air temperature never gets
down to freezing.

Peter wrote:

The temperature of a surface that's radiating heat to a clear night sky
can drop considerably below the ambient air temperature.

Err... no.

Stefan

"Stefan" wrote in message
...
Peter wrote:

The temperature of a surface that's radiating heat to a clear night sky
can drop considerably below the ambient air temperature.

Err... no.

Stefan

Err... yes.
--
Jim in NC

On Fri, 11 Feb 2005 09:26:18 -0500, "Morgans" wrote:

"Stefan" wrote in message
...
Peter wrote:

The temperature of a surface that's radiating heat to a clear night sky
can drop considerably below the ambient air temperature.

Err... no.

Err... yes.

Let me guess what's going on here.

"Ambient air temperature" means " the current local temperature of the air."
As someone said in another post, this is a fairly imprecise term and
depends on where the measurement is made at an airport.

Heat can be transferred by conduction (two masses in contact), convection
(circulation of gases or liquids), and radiation (infrared rays carry heat
away from the warm mass elsewhere).

Two masses in contact with each other (airplane skin and the air
that contacts it) have got to reach thermal equilibrium, all things
being equal and given sufficent time. Stefan seems to be focused
on this fact--the skin and the layer of air near it have to be at
the same temperature. JSM says, "But that layer of air may
be cooled more than the ambient air because the surface
loses heat not only to the ambient air but also by means of
infrared radiation."

The contrary situation certainly seems to be true: some surfaces
can be way hotter than the ambient air temperature because they
gain heat by "soaking up the sun's rays" (both infrared and visible,
I imagine). The air in contact with the hot surfaces must be in
equilibrium with the hot surface, though the air temperature would
decline to ambient air temperature as you move further away
from the surface.

Or so it seems to me.

Marty

In article ,
"Martin X. Moleski, SJ" wrote:

Two masses in contact with each other (airplane skin and the air
that contacts it) have got to reach thermal equilibrium, all things
being equal and given sufficent time.

Not quite. They have to reach thermal equilibrium if there is no heat
flowing in or out of the system. But, as you correctly note, heat can
(and doe) flow in and out via radiation. Surfaces can "soak up" the
cold of the night sky (actually, they radiate their heat into the night
sky) and become colder than the surrounding air, just as they can "soak
up" the heat of the sun and become warmer than the surrounding air.
Eventually some of the cold/heat does get transferred to the air. This
is why clear nights tend to be colder than cloudy ones (and why clear
days tend to be warmer, all else being equal).

rg

In article ,
Ron Garret wrote:

In article ,
"Martin X. Moleski, SJ" wrote:

Two masses in contact with each other (airplane skin and the air
that contacts it) have got to reach thermal equilibrium, all things
being equal and given sufficent time.

Not quite. They have to reach thermal equilibrium if there is no heat
flowing in or out of the system. But, as you correctly note, heat can
(and doe) flow in and out via radiation. Surfaces can "soak up" the
cold of the night sky (actually, they radiate their heat into the night
sky) and become colder than the surrounding air, just as they can "soak
up" the heat of the sun and become warmer than the surrounding air.
Eventually some of the cold/heat does get transferred to the air. This
is why clear nights tend to be colder than cloudy ones (and why clear
days tend to be warmer, all else being equal).


It is worth noting also that dark surfaces absorb and radiate more
readily than light ones, and so they get hotter during the day and
colder at night. Cirri are all painted white in order to take advantage
of this phenomenon and keep the skin from getting too hot in the sun.
(You'll never see a non-white Cirrus. It's part of the certification
conditions to paint the white.) Accordingly, Cirri are less prone to
radiation-induced cooling and icing than a dark-colored plane would be,
all else being equal.

FWIW,
rg

("Ron Garret" wrote)
Not quite. They have to reach thermal equilibrium if there is no heat
flowing in or out of the system. But, as you correctly note, heat can
(and doe) flow in and out via radiation. Surfaces can "soak up" the
cold of the night sky (actually, they radiate their heat into the night
sky) and become colder than the surrounding air, just as they can "soak
up" the heat of the sun and become warmer than the surrounding air.
Eventually some of the cold/heat does get transferred to the air. This
is why clear nights tend to be colder than cloudy ones (and why clear
days tend to be warmer, all else being equal).


So on the 41F night in question, and having imaginary temp probes build into
the composite wing surface, we might see overnight wing temperature readings
of say 29F or 30F?

Is there a way to (WAG), in advance, what different surface temps will be on
the night in question? (41F overnight and 40F at 8:15 am)

Knowing air temp, humidity, cloud cover, wind, etc - could someone predict
that the composite wing will be in the 25F - 31F range overnight, whereas
the aluminum wing might only get briefly down to say 35F? Aluminum being
willing to give up its heat to the air more readily than the composites?


Montblack

Stefan wrote:

Peter wrote:

The temperature of a surface that's radiating heat to a clear night sky
can drop considerably below the ambient air temperature.

Err... no.

Err ... Yes. The Romans used to make ice in North Africa by taking advantage of
this phenomena.

George Patterson
He who would distinguish what is true from what is false must have an
adequate understanding of truth and falsehood.

That's pretty cool (Pardon the pun ) Where can I read up on that George?

Patrick


"George Patterson" wrote in message
...


Stefan wrote:

Peter wrote:

The temperature of a surface that's radiating heat to a clear night sky
can drop considerably below the ambient air temperature.

Err... no.

Err ... Yes. The Romans used to make ice in North Africa by taking
advantage of
this phenomena.

George Patterson
He who would distinguish what is true from what is false must have an
adequate understanding of truth and falsehood.