Icing Airmets

[Andrew Sarangan]

I've been watching the icing airmets for some time now, and it seems
to be getting more and more conservative to the point of being
unrealistic. For example, right now the freezing level is at 5000 ft,
MEA is at 2500 ft, yet we have an airmet Z that goes all way from SFC
to 18k. How could you possibly justify such an airmet? Even though the
conditions appear to be quite good for an IFR training flight, we
still have to cancel the flight because we don't want to teach the
students that airmets can be ignored. Yet I am at a loss to explain to
them why there is an airmet when the ingredients for icing is just not
there.

The ADDS icing potential charts appear to be more realistic, but they
warn you that it supplements the Airmet and should not be used as a
substitute for icing intensity.


Any thoughts?

[ArtP]

On 26 Jan 2004 10:08:44 -0800, (Andrew
Sarangan) wrote:

>For example, right now the freezing level is at 5000 ft,
>MEA is at 2500 ft, yet we have an airmet Z that goes all way from SFC
>to 18k.

Since the published icing conditions occur from +5 to -20 C, a
freezing level at 5000 would mean icing potentially below 3000 feet.
The MEA may be 2500 but the normal minimum IFR altitudes would be
either 3000 or 4000 feet depending on direction and that is known
icing conditions. I am sorry this frustrates you but depending on
where you live a big chunk of winter is off limits to small GA
aircraft trying to fly IFR.

[Dave]

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.




"ArtP" > wrote in message
...
> On 26 Jan 2004 10:08:44 -0800, (Andrew
> Sarangan) wrote:
>
> >For example, right now the freezing level is at 5000 ft,
> >MEA is at 2500 ft, yet we have an airmet Z that goes all way from SFC
> >to 18k.
>
> Since the published icing conditions occur from +5 to -20 C, a
> freezing level at 5000 would mean icing potentially below 3000 feet.
> The MEA may be 2500 but the normal minimum IFR altitudes would be
> either 3000 or 4000 feet depending on direction and that is known
> icing conditions. I am sorry this frustrates you but depending on
> where you live a big chunk of winter is off limits to small GA
> aircraft trying to fly IFR.

[Peter R.]

Dave ) wrote:

> 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.

I have picked up ice when the digital thermometer on an '02 C172 read +3c.

--
Peter












----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---

[Dave]

How do you know your guage wasn't wrong?


"Peter R." > wrote in message
...
> Dave ) wrote:
>
> > 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.
>
> I have picked up ice when the digital thermometer on an '02 C172 read +3c.
>
> --
> Peter
>
>
>
>
>
>
>
>
>
>
>
>
> ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet
News==----
> http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000
Newsgroups
> ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption
=---

[Peter R.]

Dave ) wrote:

> How do you know your guage wasn't wrong?

The digital gauge was calibrated when new and the aircraft is about one and
one half years old. Is it possible that it slipped out of calibration a
degree or two? I suppose.

But since every icing article I have ever read states that icing can occur
at temperatures higher than 0c, I have no trouble believing that my icing
encounters above 0c actually did occur one to three degrees above 0c.



--
Peter












----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---

[Peter R.]

Dave ) wrote:

> How do you know your guage wasn't wrong?

I forgot to include the point of my adding to this thread: I use these
experiences (granted that they are somewhat limited to two winters of IFR
flying downwind of the Great Lakes, US) of encountering ice above 0c when
flight planning a cruise altitude, as well as when making a go/no decision
due to ice.

Are you implying that you are comfortable that ice will *not* occur above
0c and therefore plan accordingly?

--
Peter












----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---

[Mike Rapoport]

You can't unless your thermometer is wrong.

Mike
MU-2

"Dave" > wrote in message
ink.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.
>
>
>
>
> "ArtP" > wrote in message
> ...
> > On 26 Jan 2004 10:08:44 -0800, (Andrew
> > Sarangan) wrote:
> >
> > >For example, right now the freezing level is at 5000 ft,
> > >MEA is at 2500 ft, yet we have an airmet Z that goes all way from SFC
> > >to 18k.
> >
> > Since the published icing conditions occur from +5 to -20 C, a
> > freezing level at 5000 would mean icing potentially below 3000 feet.
> > The MEA may be 2500 but the normal minimum IFR altitudes would be
> > either 3000 or 4000 feet depending on direction and that is known
> > icing conditions. I am sorry this frustrates you but depending on
> > where you live a big chunk of winter is off limits to small GA
> > aircraft trying to fly IFR.
>
>

[Peter R.]

Mike Rapoport ) wrote:

> You can't unless your thermometer is wrong.

Are you replying to Dave's first sentence, which is:

> I'd like to know how you get in icing when the temperature is +5.

Or his second:

> I have never seen ice until the the gauge reads 0 or below.

Or both?

If you are replying to his second sentence, this is contradictory to my
understanding that the temperature right at the leading edge of an airfoil
could be up to a few degrees colder than the surrounding air, which is why
I learned that airframe icing (excluding freezing rain) can occur in air
temperatures above freezing.

I should point out here that I am simply seeking clarification of your
comment, not challenging it (as I look to you as one of the more
experienced in these groups).

--
Peter












----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---

[PaulaJay1]

In article >, Peter R.
> writes:

>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.
>
>I have picked up ice when the digital thermometer on an '02 C172 read +3c.
>

I picked up ice when my digital theromometer indicated +2 deg F. I brought it
home to calibrate it and found that it read 2 deg high at 25, 45, and 65 deg.
Pretty consistent in its error. Spec on the thermometer was plus/minus 0.5
deg. Know your own thermometer but you won't pick up ice much above 32 deg F.

Chuck

[Peter R.]

PaulaJay1 ) wrote:

> I brought it
> home to calibrate it and found that it read 2 deg high at 25, 45, and 65 deg.

How did you calibrate your thermometer for 25 degrees?

--
Peter












----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---

[Mike Rapoport]

Both sentences actually. Recent studies of airframe icing have not been
able to produce icing above 0C. (Sorry I don't have a reference). If the
static air temperature is above 0C then the water isn't supercooled, so even
if the airplane is at or slightly below freezing you won't get ice. The
wing's leading edge experiences a temperature increase, not a decrease.

I suppose that it is possible to locate the temp probe in an area with a ram
temperature rise greater than the wing. In that case, it is possible for
the temp guage to read above 0C but still have the static air temperature
and portions of the airplane below 0C. That would lead to icing but it is
an instrument error not icing above 0C.

Mike
MU-2


"Peter R." > wrote in message
...
> Mike Rapoport ) wrote:
>
> > You can't unless your thermometer is wrong.
>
> Are you replying to Dave's first sentence, which is:
>
> > I'd like to know how you get in icing when the temperature is +5.
>
> Or his second:
>
> > I have never seen ice until the the gauge reads 0 or below.
>
> Or both?
>
> If you are replying to his second sentence, this is contradictory to my
> understanding that the temperature right at the leading edge of an airfoil
> could be up to a few degrees colder than the surrounding air, which is why
> I learned that airframe icing (excluding freezing rain) can occur in air
> temperatures above freezing.
>
> I should point out here that I am simply seeking clarification of your
> comment, not challenging it (as I look to you as one of the more
> experienced in these groups).
>
> --
> Peter
>
>
>
>
>
>
>
>
>
>
>
>
> ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet
News==----
> http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000
Newsgroups
> ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption
=---

[Dave]

Yes I am comfortable flying in temperatures above 0 and I do plan
accordingly. Although as soon as I see 0 on the OAT then I also plan
accordingly. (Like change altitude , turn around, land etc.)
"Peter R." > wrote in message
...
> Dave ) wrote:
>
> > How do you know your guage wasn't wrong?
>
> I forgot to include the point of my adding to this thread: I use these
> experiences (granted that they are somewhat limited to two winters of IFR
> flying downwind of the Great Lakes, US) of encountering ice above 0c when
> flight planning a cruise altitude, as well as when making a go/no decision
> due to ice.
>
> Are you implying that you are comfortable that ice will *not* occur above
> 0c and therefore plan accordingly?
>
> --
> Peter
>
>
>
>
>
>
>
>
>
>
>
>
> ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet
News==----
> http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000
Newsgroups
> ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption
=---

[Bob Gardner]

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. That's why you look at those surfaces
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

"Dave" > wrote in message
ink.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.
>
>
>
>
> "ArtP" > wrote in message
> ...
> > On 26 Jan 2004 10:08:44 -0800, (Andrew
> > Sarangan) wrote:
> >
> > >For example, right now the freezing level is at 5000 ft,
> > >MEA is at 2500 ft, yet we have an airmet Z that goes all way from SFC
> > >to 18k.
> >
> > Since the published icing conditions occur from +5 to -20 C, a
> > freezing level at 5000 would mean icing potentially below 3000 feet.
> > The MEA may be 2500 but the normal minimum IFR altitudes would be
> > either 3000 or 4000 feet depending on direction and that is known
> > icing conditions. I am sorry this frustrates you but depending on
> > where you live a big chunk of winter is off limits to small GA
> > aircraft trying to fly IFR.
>
>

[PaulaJay1]

In article >, Peter R.
> writes:

>> I brought it
>> home to calibrate it and found that it read 2 deg high at 25, 45, and 65
>deg.
>
>How did you calibrate your thermometer for 25 degrees?
>

I put it and two reference thermometers in the freezer part of the
refrigerator. I put them in the full freezer that is about 0 deg F and the
digital did not display. Don't know if the battery was weak or the electronics
just gave out. I didn't think that this was a problem since the inside of the
plane is at least 25deg F <G> or higher. The 45 deg was the refrigerator and
the 65 was outside temperature.

Chuck

[Andrew Sarangan]

The temperature above the wings and below the elevators could be
slightly below ambient due to the lower pressure. I don't have a
number on what the temperature drop is on these surfaces, but
technically it is possible to have icing on the lifting surfaces when
the ambient temperature is above freezing. Sort of like carb icing in
above-freezing temperatures.


"Mike Rapoport" > wrote in message . net>...
> You can't unless your thermometer is wrong.
>
> Mike
> MU-2
>
> "Dave" > wrote in message
> ink.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.
> >
> >
> >
> >
> > "ArtP" > wrote in message
> > ...
> > > On 26 Jan 2004 10:08:44 -0800, (Andrew
> > > Sarangan) wrote:
> > >
> > > >For example, right now the freezing level is at 5000 ft,
> > > >MEA is at 2500 ft, yet we have an airmet Z that goes all way from SFC
> > > >to 18k.
> > >
> > > Since the published icing conditions occur from +5 to -20 C, a
> > > freezing level at 5000 would mean icing potentially below 3000 feet.
> > > The MEA may be 2500 but the normal minimum IFR altitudes would be
> > > either 3000 or 4000 feet depending on direction and that is known
> > > icing conditions. I am sorry this frustrates you but depending on
> > > where you live a big chunk of winter is off limits to small GA
> > > aircraft trying to fly IFR.
> >
> >

[Doug]

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.
If you get ice on your themometer and it reads above zero, your
themometer is out of calibration.


Peter R. > wrote in message >...
> Dave ) wrote:
>
> > How do you know your guage wasn't wrong?
>
> The digital gauge was calibrated when new and the aircraft is about one and
> one half years old. Is it possible that it slipped out of calibration a
> degree or two? I suppose.
>
> But since every icing article I have ever read states that icing can occur
> at temperatures higher than 0c, I have no trouble believing that my icing
> encounters above 0c actually did occur one to three degrees above 0c.
>
>
>
> --
> Peter
>
>
>
>
>
>
>
>
>
>
>
>
> ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==----
> http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
> ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---

[Andrew Sarangan]

This is not about frustration, but about trying to understanding how
FAA comes up with airmets. An airmet is supposed to be issued when
moderate icing is expected. If they are issuing an airmet every time
there are clouds and freezing temperatures (or even above freezing),
then what about light icing?




ArtP > wrote in message >...
> On 26 Jan 2004 10:08:44 -0800, (Andrew
> Sarangan) wrote:
>
> >For example, right now the freezing level is at 5000 ft,
> >MEA is at 2500 ft, yet we have an airmet Z that goes all way from SFC
> >to 18k.
>
> Since the published icing conditions occur from +5 to -20 C, a
> freezing level at 5000 would mean icing potentially below 3000 feet.
> The MEA may be 2500 but the normal minimum IFR altitudes would be
> either 3000 or 4000 feet depending on direction and that is known
> icing conditions. I am sorry this frustrates you but depending on
> where you live a big chunk of winter is off limits to small GA
> aircraft trying to fly IFR.

[Roy Smith]

In article >,
(Andrew Sarangan) wrote:

> The temperature above the wings and below the elevators could be
> slightly below ambient due to the lower pressure. I don't have a
> number on what the temperature drop is on these surfaces, but
> technically it is possible to have icing on the lifting surfaces when
> the ambient temperature is above freezing. Sort of like carb icing in
> above-freezing temperatures.

You're talking about two very very different things.

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? You think I'm trying to befuddle
the issue with big-sounding words like "adiabatic"? OK, all adiabatic
means is that there's no exchange of heat. We all know that gasses get
hotter when you compress them. You probably learned Boyle's Law and
Charles's Law in high school chemistry, or maybe the Ideal Gas Law.
These are all just different ways of saying that if you've got a certain
amount of gas which contains a certain amount of energy, if you know any
two of pressure, volume, and temperature, you can figure out the third.
As long as you don't add or subtract energy (i.e. heat), you can play
with those three variables to get all sorts of different combinations.

All those "no heat lost or gained" transitions are adiabatic. That's
what happens at the leading edge. The air moves from an area of high
pressure to an area of lower pressure on top of the wing. As it does,
it expands and cools, but the total amount of energy in a given parcel
of air stays the same.

This is not to say that adiabatic cooling can't cause very large
temperature drops. Anybody who has ever fired off a CO2 fire
extinguisher knows that the gas coming out is VERY cold, and that is an
adiabatic process. But it's also undergoing a pressure drop orders of
magnitude bigger than what goes on at the leading edge of a spam can.

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. The air that enters the carburator is NOT undergoing an
adiabatic process; it's giving up energy to the gas to make it vaporize.
That's why you get huge temperature drops inside the carb, and can get
carb icing at ambient temperatures way above freezing.

[ArtP]

On Tue, 27 Jan 2004 20:33:12 -0500, Roy Smith > wrote:

>
>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.

That is all we are discussing, whether the FAA +5 to -20 is a
reasonable range for icing.

[ArtP]

On 27 Jan 2004 17:05:49 -0800, (Andrew
Sarangan) wrote:

>This is not about frustration, but about trying to understanding how
>FAA comes up with airmets. An airmet is supposed to be issued when
>moderate icing is expected. If they are issuing an airmet every time
>there are clouds and freezing temperatures (or even above freezing),
>then what about light icing?

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..

[C J Campbell]

"Dave" > wrote in message
ink.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.

Per your next reply -- if you don't trust Peter R.'s gauge to say it is +3
when he is getting icing, what makes you think you can trust your gauge?

[C J Campbell]

"PaulaJay1" > wrote in message
...
| In article >, Peter R.
| > writes:
|
| >> I brought it
| >> home to calibrate it and found that it read 2 deg high at 25, 45, and
65
| >deg.
| >
| >How did you calibrate your thermometer for 25 degrees?
| >
|
| I put it and two reference thermometers in the freezer part of the
| refrigerator. I put them in the full freezer that is about 0 deg F and
the
| digital did not display.

Digital displays usually fail in cold temperatures. There is nothing odd
about that.

[Mike Rapoport]

"Andrew Sarangan" > wrote in message
om...
> The temperature above the wings and below the elevators could be
> slightly below ambient due to the lower pressure. I don't have a
> number on what the temperature drop is on these surfaces, but
> technically it is possible to have icing on the lifting surfaces when
> the ambient temperature is above freezing. Sort of like carb icing in
> above-freezing temperatures.
>

There has been a lot of hypothisizing about this in the past but NOBODY has
EVER been able to reproduce it.

You don't get icing just because a portion of the airplane is below 0C. I
doubt if droplets even touch any part of the airfoil where the
temperature/preasure is below ambient without running back. If they run
back, the first encountered the heated portion of the wing (leading edge).
You need supercooled water to get airframe icing.

It is another of aviations myths

Mike
MU-2
..

[Mike Rapoport]

"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.

Mike
MU-2

[Mike Rapoport]

"C J Campbell" > wrote in message
...
>
> "Dave" > wrote in message
> ink.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.

Mike
MU-2

[Gerald Sylvester]

>>This is not about frustration, but about trying to understanding how
>>FAA comes up with airmets. An airmet is supposed to be issued when
>>moderate icing is expected. If they are issuing an airmet every time
>>there are clouds and freezing temperatures (or even above freezing),
>>then what about light icing?
> 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..

The other crazy thing is people are arguing over 2 degrees F. I don't
care how accurate your thermometer is, but if you are that close
to potential icing, get out of there. +5 certainly gives you the
margin and sure the FAA will err on the larger side but still,
are you watching the OAT in your instrument scan....."one more
degree drop and I turn around....." Crazy.

Gerald

[Peter R.]

Gerald Sylvester ) wrote:

> are you watching the OAT in your instrument scan....."one more
> degree drop and I turn around....." Crazy.

LOL!

--
Peter












----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =---

[Andrew Sarangan]

Roy
Thanks for that explanation. I did not realize that it was evaporative
cooling that was the cause of cooling in the carb. A lot of texts out
there describe that the cooling is due to pressure drop. It makes
sense that evaporation gives out a lot more energy than adiabatic
expansion.


Roy Smith > wrote in message >...
> In article >,
> (Andrew Sarangan) wrote:
>
> > The temperature above the wings and below the elevators could be
> > slightly below ambient due to the lower pressure. I don't have a
> > number on what the temperature drop is on these surfaces, but
> > technically it is possible to have icing on the lifting surfaces when
> > the ambient temperature is above freezing. Sort of like carb icing in
> > above-freezing temperatures.
>
> You're talking about two very very different things.
>
> 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? You think I'm trying to befuddle
> the issue with big-sounding words like "adiabatic"? OK, all adiabatic
> means is that there's no exchange of heat. We all know that gasses get
> hotter when you compress them. You probably learned Boyle's Law and
> Charles's Law in high school chemistry, or maybe the Ideal Gas Law.
> These are all just different ways of saying that if you've got a certain
> amount of gas which contains a certain amount of energy, if you know any
> two of pressure, volume, and temperature, you can figure out the third.
> As long as you don't add or subtract energy (i.e. heat), you can play
> with those three variables to get all sorts of different combinations.
>
> All those "no heat lost or gained" transitions are adiabatic. That's
> what happens at the leading edge. The air moves from an area of high
> pressure to an area of lower pressure on top of the wing. As it does,
> it expands and cools, but the total amount of energy in a given parcel
> of air stays the same.
>
> This is not to say that adiabatic cooling can't cause very large
> temperature drops. Anybody who has ever fired off a CO2 fire
> extinguisher knows that the gas coming out is VERY cold, and that is an
> adiabatic process. But it's also undergoing a pressure drop orders of
> magnitude bigger than what goes on at the leading edge of a spam can.
>
> 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. The air that enters the carburator is NOT undergoing an
> adiabatic process; it's giving up energy to the gas to make it vaporize.
> That's why you get huge temperature drops inside the carb, and can get
> carb icing at ambient temperatures way above freezing.

[Andrew Sarangan]

ArtP > wrote in message >...
> On 27 Jan 2004 17:05:49 -0800, (Andrew
> Sarangan) wrote:
>
> >This is not about frustration, but about trying to understanding how
> >FAA comes up with airmets. An airmet is supposed to be issued when
> >moderate icing is expected. If they are issuing an airmet every time
> >there are clouds and freezing temperatures (or even above freezing),
> >then what about light icing?
>
> 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?

[ArtP]

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.

[Roy Smith]

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.

[Mike Rapoport]

"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

[Icebound]

Mike Rapoport wrote:
> "C J Campbell" > wrote in message
> ...
>
>>"Dave" > wrote in message
ink.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.

[Dave]

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
> ink.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.
>
>

[Mike Rapoport]

"Icebound" > wrote in message
ble.rogers.com...
> Mike Rapoport wrote:
> > "C J Campbell" > wrote in message
> > ...
> >
> >>"Dave" > wrote in message
> ink.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

[Tarver Engineering]

"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.

[Tarver Engineering]

"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.

[Tarver Engineering]

"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.

[Roy Smith]

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?

[Tarver Engineering]

"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.

[Mike Rapoport]

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.
>
>

[Tarver Engineering]

"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]

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.
> > >
> > >
> >
> >
>
>

[Tarver Engineering]

"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]

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.
>
>

[Tarver Engineering]

"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]

"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.

[Michael]

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

[Julian Scarfe]

"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=1ADJ9.172%24Pn2.38474%40newsfep1-win.server.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

[Michael]

"Mike Rapoport" > wrote
> 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.

Yeah, but you do hear about one falling out of the sky every once in a
while.

> 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.

The trick, of course, is recognizing the 1% you can't fly in before
it's too late.

> 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.

A good friend of mine has lots of experience in known-ice piston twins
(acquired on the way up to the airlines) and gave me some advice when
it looked like I might be moving into one (when it looked like I might
have to move North for professional reasons). His position is that
flying a piston airplane in icing conditions requires careful
attention to maintenance (his experience is that most piston deice
systems are poorly maintained) and a significantly greater level of
weather savvy and skill (relative to flying a jet, which requires none
- all icing problem go away at 400 kts indicated) but it can be done,
and will allow the completion of the vast majority of missions in
icing conditions.

I suspect it's similar to the Stormscope vs. RADAR deal. I hear
people say that a Stromscope is just a way of knowing that there's
stuff out there and it's time to land, not a way of flying around
T-storms. In reality, I live in T-storm central and have yet to
cancel a flight because of T-storms. I have made some deviations, but
so does a RADAR-equipped airplane. I have had some tense moments, and
obviously having RADAR would have been better. Of course this is
predicated on the Stormscope working properly. Proper operation means
that when the sky is dead (meaning the air is smooth as glass, and any
clouds are stratiform) you can fly around for hours without seeing a
dot on the most sensitive setting. In reality, most avionics shops
are not competent to perform such an installation and less than 20% of
spherics devices function that way.

These are simply specific instances of a more general rule - if you
want to fly difficult weather in less capable equipment, you need to
be a more capable pilot, but it can usually be done.

Michael

[Ray Andraka]

It is possible to get icing if you were recently in colder air such that the airframe got cold-soaked and has not warmed to above
freezing yet. I've picked up ice in a descent that way before, but it doesn't take long before it goes way.

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759