Weather Flying - Buck

A Lieberman wrote:

Never had icing, however, one lesson my CFI and I were in clouds right at
32 degrees. Water was beading up the windscreen, so as long as that was
happening, we were reasonably safe.

I wouldn't trust that at all. The collection efficiency for ice
increases as the surface gets narrower (towards the wind), so you can
have ice on your antennas when there's still water on your tail; ice on
your tail when there's still water on your wings; and ice on your wings
when there's still water on your windshield.

Fortunately, my Warrior (like most or all Piper PA-28 models) has an
outside air temperature gauge with a long metal probe sticking straight
out into the airstream from the middle of the windshield. Because the
probe is so narrow, ice will form on it before just about anything else
(except maybe the antennas, which I cannot see). I use it as my
early-warning device, and divert to warmer and/or dryer conditions as
soon as the first tiny piece of ice forms on the end of the probe.


All the best,


David

Fortunately, my Warrior (like most or all Piper PA-28 models) has an
outside air temperature gauge with a long metal probe sticking straight
out into the airstream from the middle of the windshield. Because the
probe is so narrow, ice will form on it before just about anything else
(except maybe the antennas, which I cannot see). I use it as my
early-warning device, and divert to warmer and/or dryer conditions as
soon as the first tiny piece of ice forms on the end of the probe.

Don't count on it. I flew into ice in the Blue Ridge mountains; I was
keeping a good eye on that temperature probe and other things sticking
out, but the wings got what I now in retrospect realize was a nice
coating of clear ice while the probe stayed clean as a whistle. Then
all of a sudden the windshield iced up - bang.

I declared an emergency and got vectors to warmer air and an ILS. It
took a while for the ice to come off, but it did before I landed.

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

wrote:
A Lieberman wrote:


Never had icing, however, one lesson my CFI and I were in clouds right at
32 degrees. Water was beading up the windscreen, so as long as that was
happening, we were reasonably safe.


I wouldn't trust that at all. The collection efficiency for ice
increases as the surface gets narrower (towards the wind), so you can
have ice on your antennas when there's still water on your tail; ice on
your tail when there's still water on your wings; and ice on your wings
when there's still water on your windshield.

Do you have a freezer in your antennas that freezes the water on them
when it is still above freezing elsewhere (i.e., water on the tail)?


Fortunately, my Warrior (like most or all Piper PA-28 models) has an
outside air temperature gauge with a long metal probe sticking straight
out into the airstream from the middle of the windshield. Because the
probe is so narrow, ice will form on it before just about anything else
(except maybe the antennas, which I cannot see). I use it as my
early-warning device, and divert to warmer and/or dryer conditions as
soon as the first tiny piece of ice forms on the end of the probe.

Yes, ice will form first on small radius surfaces, but not until at or
below freezing temperatures. If you still have water on your wings or
tail, then you won't have ice on your OAT probe.


Matt

Matt Whiting wrote:

Yes, ice will form first on small radius surfaces, but not until at or
below freezing temperatures. If you still have water on your wings or
tail, then you won't have ice on your OAT probe.

From what I've observed so far, there's a zone of ambiguity between
about 1 degC and -5 degC where supercooled droplets may or may not
stick to the airframe as ice. I've seen ice form on the tip of my OAT
probe while there were still drops of water running down its sides, as
well as over the rest of the airframe. Freezing is not an
all-or-nothing proposition.


All the best,


David

wrote in message
oups.com...
A Lieberman wrote:

Never had icing, however, one lesson my CFI and I were in clouds right at
32 degrees. Water was beading up the windscreen, so as long as that was
happening, we were reasonably safe.

I wouldn't trust that at all. The collection efficiency for ice
increases as the surface gets narrower (towards the wind), so you can
have ice on your antennas when there's still water on your tail; ice on
your tail when there's still water on your wings; and ice on your wings
when there's still water on your windshield.

Fortunately, my Warrior (like most or all Piper PA-28 models) has an
outside air temperature gauge with a long metal probe sticking straight
out into the airstream from the middle of the windshield. Because the
probe is so narrow, ice will form on it before just about anything else
(except maybe the antennas, which I cannot see). I use it as my
early-warning device, and divert to warmer and/or dryer conditions as
soon as the first tiny piece of ice forms on the end of the probe.


All the best,


David


Whether the droplets are supercooled or not has nothing to do with
collection efficiency. Collection efficiency is simply the number of
droplets which impact a surface instead of going around it with the airflow.
Collection efficiency is a function of the mass of the droplets, airspeed
and the size and radius of the collecting surface. If the droplets hitting
the windscreen are not freezing (assuming the windscreen is not heated) then
the droplets hitting the tail are not freezing either.

Mike
MU-2

If the droplets hitting the windscreen are not
freezing (assuming the windscreen is not heated) then
the droplets hitting the tail are not freezing either.

I don't think that's true at all. The airflow around the windscreen is
different from the airflow around the tail. The temperature of the
inside of the cockpit (which influences the outside of the windscreen)
is different from the temperature inside the tail. The heat capacity of
aluminum is different from the heat capacity of plexiglass. All these
impact collection efficiency.

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

collection efficiency is a measure of what percentage of droplets will hit
the surface...nothing more. It has nothing to do with *whether* ice will
form on a surface, only how much.

Mike
MU-2


"Jose" wrote in message
...
If the droplets hitting the windscreen are not freezing (assuming the
windscreen is not heated) then the droplets hitting the tail are not
freezing either.

I don't think that's true at all. The airflow around the windscreen is
different from the airflow around the tail. The temperature of the inside
of the cockpit (which influences the outside of the windscreen) is
different from the temperature inside the tail. The heat capacity of
aluminum is different from the heat capacity of plexiglass. All these
impact collection efficiency.

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

collection efficiency is a measure of what percentage of droplets will hit
the surface...nothing more. It has nothing to do with *whether* ice will
form on a surface, only how much.

Ok, then collection efficiency is not a good measure of what's
important. What I care about is how much of that water will be
=retained= ("collected") as ice.

So, I am concerned about retention efficiency.

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