Icing Airmets

"Roy Smith" wrote in message
...
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?

Liquid water tends to have both hydrogen atoms on the same side of the
molecule; 60 degress apart IIRC. The phase change from liquid to soild
water causes the hydrogen attoms to be 180 degrees apart and the molecule to
become larger. There is a specific amount of energy expelled for each
molecule to go through this phase change and it is large. This quantum
aspect of the liquid/solid phase change causes icing to be a statistical
process and invalidates the wind tunnel data.

If you say so John but you never present any evidence or reference to back
up your assertions. Small droplets are not a major icing hazard because
they freeze right at the leading edge..

Mike
MU-2

"Tarver Engineering" wrote in message
...

"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.

"Mike Rapoport" wrote in message
nk.net...
If you say so John but you never present any evidence or reference to back
up your assertions. Small droplets are not a major icing hazard because
they freeze right at the leading edge..

I'll take Brownlee's FAA flight test over you any day, Rapport.

"Tarver Engineering" wrote in message
...

"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.

Why don't you post some data from Mr. Brownlee then. Or even his opinion.

Mike
MU-2


"Tarver Engineering" wrote in message
...

"Mike Rapoport" wrote in message
nk.net...
If you say so John but you never present any evidence or reference to
back
up your assertions. Small droplets are not a major icing hazard because
they freeze right at the leading edge..

I'll take Brownlee's FAA flight test over you any day, Rapport.

"Tarver Engineering" wrote in message
...

"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.

"Mike Rapoport" wrote in message
ink.net...
Why don't you post some data from Mr. Brownlee then. Or even his opinion.

Call Joe on the telephone and ask him yourself, Rapoport, he is one hell of
a nice guy.

So you really don't have anything that supports your position which
contradicts all published information from all sources.

Mike
MU-2


"Tarver Engineering" wrote in message
...

"Mike Rapoport" wrote in message
ink.net...
Why don't you post some data from Mr. Brownlee then. Or even his
opinion.

Call Joe on the telephone and ask him yourself, Rapoport, he is one hell
of
a nice guy.

"Mike Rapoport" wrote in message
nk.net...
So you really don't have anything that supports your position which
contradicts all published information from all sources.

All I have is my conversation with Brownlee and his flight test pilot staff.
At the standrdization seminar's conclusion they all gathered around me while
Joe made the small droplet statement and they wanted soemthing from me on
probabilities. The FAA flight test pilot staff that flew the actual flights
of the large droplet study were there. Their conclusion was that the
original assumption of lthe large droplet icing study was completely wrong
and I made the comment that perhaps they could get new funding to study
small droplets; everyone laughed.

I believe the results of the flight test are published, but I am not going
to search it up for you.


"Tarver Engineering" wrote in message
...

"Mike Rapoport" wrote in message
ink.net...
Why don't you post some data from Mr. Brownlee then. Or even his
opinion.

Call Joe on the telephone and ask him yourself, Rapoport, he is one hell
of
a nice guy.

"Tarver Engineering" wrote in message
...

"Mike Rapoport" wrote in message
nk.net...
So you really don't have anything that supports your position which
contradicts all published information from all sources.

All I have is my conversation with Brownlee and his flight test pilot
staff.
At the standrdization seminar's conclusion they all gathered around me
while
Joe made the small droplet statement and they wanted soemthing from me on
probabilities. The FAA flight test pilot staff that flew the actual
flights
of the large droplet study were there. Their conclusion was that the
original assumption of lthe large droplet icing study was completely wrong
and I made the comment that perhaps they could get new funding to study
small droplets; everyone laughed.

I believe the results of the flight test are published, but I am not going
to search it up for you.

As an adendum:

Keep in mind that aero engineers have a very difficult time dealing with
their own data and equations being false. As an example, the Law of the
Wall was removed as a regulatory hurdle, once it was pointed out that the
Law is dimensionally without any basis in physical reality; yet some aero
engineering schools still teach the Law of the Wall.

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

"Roy Smith" wrote in message
...

When a gas undergoes adiabatic expansion, it gets cooler. There is no
doubt that this happens at the leading edges of airfoils, but at the
pressure drops we're talking about in any kind of airplane I'm likely to
fly is very small. How small is very small? I'm not sure, but I can't
imagine more than a degree or two.

Yes, you in the back? What's that?

Have you been sleeping in class *again* Dr Smith? :-)

http://groups.google.com/groups?selm...erver.ntli.net

(Actually Roy, you're correct.)

The summary was:

--
1) I assert that airframe icing can only occur at points on the airframe
where the static temperature is below freezing.

2) Since the pressure over the top surface of a wing is less than the
freestream pressure, the associated reduction in temperature can cause the
airframe to be cooler than the temperature indicated on an OAT probe.

3) I find that the difference in temperature between indicated OAT and the
coolest part of the wing is proportional to the wing loading of the aircraft
divided by the freestream pressure, and varies a little with AOA.

4) For light aircraft, the difference in temperature between indicated OAT
and the coolest part of the wing is unlikely to exceed about 1 degC. For
big jets, the difference in temperature is unlikely to exceed about 10 degC.
--

Mike suggests (and I think he suggested in Dec 2002 when I wrote the article
cited above) that the rate of cooling of water droplets is such that water
droplets above 0 degC will not freeze on running back on a wing that has a
part of it that is sub-zero. I haven't done that particular sum, so won't
comment on that until I have.

Julian Scarfe