snow and icing

Ok, so it's snowing out. Presumably the water in the clouds is all frozen and
there should be no icing concerns. Under what circumstances am I wrong?

Jose

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In article , Teacherjh
wrote:

Ok, so it's snowing out. Presumably the water in the clouds is all frozen and
there should be no icing concerns. Under what circumstances am I wrong?

An inversion aloft. The air gets warmer as you climb, up to a point.

Most of the time there will be some ice as all of the water is not frozen.
Often snow does not come from clouds at all but goes directly from a vapor
to a crystal. In that cast there is no cloud and no ice. Today it was
snowing heavily on the ground where it was -1C and I found ice in the clouds
all the way to the tops at about 16,000' where it was below -20C (most of
the ice was lower however).

If the snow is the pellet type it is formed by liquid droplets freezing
together, so there is definately liquid water in clouds producing this kind
of snow.

..
Mike
MU-2



"Teacherjh" wrote in message
...
Ok, so it's snowing out. Presumably the water in the clouds is all frozen
and
there should be no icing concerns. Under what circumstances am I wrong?

Jose

--
(for Email, make the obvious changes in my address)

Teacherjh wrote:
Ok, so it's snowing out. Presumably the water in the clouds is all frozen and
there should be no icing concerns. Under what circumstances am I wrong?

You are flying a Cessna Skylane with the air intake under the spinner.
Heavy snow can clog it requiring you to fly with carb heat applied
causing a measurable loss of manifold pressure.

Also, prior to having static wicks installed, I got a very bad case of
p-static when flying in cold snow. Couldn't hear the controller on the
radio at all for 15 minutes. Not an icing problem per se, but a problem
caused by flying in "dry" snow.


Matt

Matthew S. Whiting wrote:

You are flying a Cessna Skylane with the air intake under the spinner.
Heavy snow can clog it requiring you to fly with carb heat applied
causing a measurable loss of manifold pressure.

The later model C172s and 182s have an automatic alternate air feature
that will pull air from within the engine cavity if the air intake below
the spinner clogs up.

The pilot can expect a drop in RPMs of about 10% if this occurs.

--
Peter










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Peter R. wrote:
The later model C172s and 182s have an automatic alternate air feature
that will pull air from within the engine cavity if the air intake below
the spinner clogs up.

Don't all planes? It's a prety common feature that the alternate air
door is spring loaded. Pulling the carb heat (or alternate air) knob
will pull the door open, but even without pulling the knob, if the
pressure differential gets too high (i.e. the intake is clogged), the
door will open on its own against spring pressure.

Roy Smith wrote:

Don't all planes?

I do not know. I interpreted the previous poster to imply that pilots
of all C182 models had to pull the carb heat if the front air intake
clogged. Thus, I offered what little aircraft knowledge I have about
the later fuel-injected models that do not have a carb heat or alternate
air lever inside the cockpit.

It's a prety common feature that the alternate air
door is spring loaded.

OK, I'll take your word for it.

Pulling the carb heat (or alternate air) knob
will pull the door open, but even without pulling the knob, if the
pressure differential gets too high (i.e. the intake is clogged), the
door will open on its own against spring pressure.

Roger.

--
Peter










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In article , Teacherjh
wrote:

Ok, so it's snowing out. Presumably the water in the clouds is all frozen and
there should be no icing concerns. Under what circumstances am I wrong?

If it is snowing dry snow and the temp is well below freezing you can
pretty much discount ice if you remain clear of clouds. The snow may
clog the air intake, but ice will not accrete on the leading edges.

If you get up into clouds, however, regardless of whether snow is
falling below the clouds, you should probably be prepared for ice
accretion because in the clouds the water will most likely not be
completely frozen, unless the temperature is VERY low and you will
encounter supercooled droplets which will freeze when they hit the
airframe.

Peter R. wrote:
Matthew S. Whiting wrote:


You are flying a Cessna Skylane with the air intake under the spinner.
Heavy snow can clog it requiring you to fly with carb heat applied
causing a measurable loss of manifold pressure.


The later model C172s and 182s have an automatic alternate air feature
that will pull air from within the engine cavity if the air intake below
the spinner clogs up.

The pilot can expect a drop in RPMs of about 10% if this occurs.


The 182 shouldn't lose RPM if the prop governor is working correctly.


Matt

Roy Smith wrote:
Peter R. wrote:

The later model C172s and 182s have an automatic alternate air feature
that will pull air from within the engine cavity if the air intake below
the spinner clogs up.


Don't all planes? It's a prety common feature that the alternate air
door is spring loaded. Pulling the carb heat (or alternate air) knob
will pull the door open, but even without pulling the knob, if the
pressure differential gets too high (i.e. the intake is clogged), the
door will open on its own against spring pressure.

My Skylane didn't open automatically. I don't know if it was designed
to or not, but I know it didn't. At least not completely, and partial
carb heat was often worse than none at all.


Matt