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Old 09-16-2020, 10:30 PM   #71  
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Originally Posted by Ace66 View Post
No sir, not a myth - an actual meteorological term. And you are wrong, fog is water vapor that is condensing because the air is oversaturated. I've never seen fog on a surface. Did you perhaps mean to say....dew?


There's frost and then there's hoarfrost. By definition hoarfrost goes from the vapor state to the solid state. It can be brushed off the surface. Think about two pieces of lead at room temperature. Put them together - no adhesion. Heat one to the melting point and then touch the solid piece and then cool to room temp - it adheres. Think of dry snow falling on a wing cold soaked at -20degC. Are you telling me that snow will adhere?


"While hoarfrost forms directly on objects as ice crystals, rime forms when tiny, near-freezing water droplets, usually from thick fog and other clouds, attach to the surface of a below-freezing object and turn into ice immediately on contact."

https://www.accuweather.com/en/weath...hoarfrost/7092


Hoarfrost is described in many meteorological texts. Frost - AMS Glossary for an easy one.


Regardless, even if that frost did adhere to the wing like window frost, it would not affect the airflow. It's thin enough to see through it, it's on the aft portion of the wing, and it's far smoother than the screw heads, access panels, and other structure on the wing. But we continue to waste money and the environment on spraying clean wings because every uneducated idiot like this guy has a phone camera and the FSDO on speed dial.

Not sure why the "former bush pilot" comment was made. Dogma? Ok let's go - four years conducting aviation weather research including aircraft icing for a government lab funded by the FAA and years designing jets for Boeing as an aerospace engineer. Oh yea and I flew a 1941 warbird with a 65hp engine, no GPS, no electrical above the arctic circle - in the bush. Oh and I've flown a CRJ200 (supercritical wing) with the typical outer 4 wing panels having hoarfrost on them. If you want to pull out resumes and compare who's bigger, I'm game. But I'd rather argue physics. Crack a book sometime.
Regular frost also goes from the vapor state to the solid state. It's just the extent of the crystals and that hoarfrost only forms by deposition. You are trying to somehow claim that hoarfrost doesn't adhere because it uniquely goes from a gas to a solid? While the crystals can be broken quite easily, they are still attached at the base. See my comment at the end.

Quote:
Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above freezing atmosphere coming in contact with a solid surface whose temperature is below freezing,[1][2] and resulting in a phase change from water vapor (a gas) to ice (a solid) as the water vapor reaches the freezing point. In temperate climates, it most commonly appears on surfaces near the ground as fragile white crystals; in cold climates, it occurs in a greater variety of forms.[3] The propagation of crystal formation occurs by the process of nucleation.

The ice crystals of frost form as the result of fractal process development. The depth of frost crystals varies depending on the amount of time they have been accumulating, and the concentration of the water vapor (humidity). Frost crystals may be invisible (black), clear (translucent), or white; if a mass of frost crystals scatters light in all directions, the coating of frost appears white.

Types of frost include crystalline frost (hoar frost or radiation frost) from deposition of water vapor from air of low humidity, white frost in humid conditions, window frost on glass surfaces, advection frost from cold wind over cold surfaces, black frost without visible ice at low temperatures and very low humidity, and rime under supercooled wet conditions.[3]
You are clearly cherry-picking what we are saying. No one is saying that hoarfrost is not a meteorological term or phenomenon, only that it's simply the extent to which the crystals grow based on higher humidity. It's still frost. You are attempting to make it out to be something it is not. It still adheres to surfaces just like any other frost...because it is frost.

The reference that we were asking for was the one that says it doesn't adhere to surfaces.

If you want to use the cold wing scenario, a cold-soaked fuel tank can make frost deposit directly on the fuel tank area even when there's no frost in the environment otherwise and the air temperature is well above freezing. It's the same mechanism. It adheres and no, it doesn't just brush off.

Due to the low sun and cold temps, hoarfrost often forms on our car windows in the winter time, even in the daytime, so we spend a few minutes scraping it off. Forms on the metal body as well. Sometimes it's damn near impossible to get off without heating the car from the inside to at least partially melt it. If it behaved as you claim, I could just blow it off with my breath.

The only situations I've observed in Alaska where ice does not adhere is dry snow when it's below freezing (I've seen this upset by various factors too, can't just assume it) and ice-fog under the same conditions. I've never seen a form of frost that can be brushed or polished off. I've seen plenty of people try...but it's still there after they attempt to brush/polish it. You seem to be implying the "polish smooth" thing about it...

My own pic:
Attached Images
File Type: jpg 0118832284351d5a9a15576d244919b50b2474a45fss.jpg (118.7 KB, 125 views)

Last edited by JamesNoBrakes; 09-16-2020 at 10:59 PM.
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Old 09-17-2020, 08:31 AM   #72  
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Originally Posted by JamesNoBrakes View Post
Regular frost also goes from the vapor state to the solid state. It's just the extent of the crystals and that hoarfrost only forms by deposition. You are trying to somehow claim that hoarfrost doesn't adhere because it uniquely goes from a gas to a solid? While the crystals can be broken quite easily, they are still attached at the base. See my comment at the end.

No, not all frost goes directly to the solid state:

Window frost

Window frost (also called fern frost or ice flowers) forms when a glass pane is exposed to very cold air on the outside and warmer, moderately moist air on the inside. If the pane is not a good insulator (for example, if it is a single pane window), water vapour condenses on the glass forming frost patterns. With very low temperatures outside, frost can appear on the bottom of the window even with double pane energy efficient windows because the air convection between two panes of glass ensures that the bottom part of the glazing unit is colder than the top part. On unheated motor vehicles the frost will usually form on the outside surface of the glass first. The glass surface influences the shape of crystals, so imperfections, scratches, or dust can modify the way ice nucleates. The patterns in window frost form a fractal with a fractal dimension greater than one but less than two. This is a consequence of the nucleation process being constrained to unfold in two dimensions, unlike a snowflake which is shaped by a similar process but forms in three dimensions and has a fractal dimension greater than two.[8]


If the indoor air is very humid, rather than moderately so, water will first condense in small droplets and then freeze into clear ice.


Similar patterns of freezing may occur on other smooth vertical surfaces, but they seldom are as obvious or spectacular as on clear glass.


Quote:
No one is saying that hoarfrost is not a meteorological term or phenomenon, only that it's simply the extent to which the crystals grow based on higher humidity.

Yes, zerozero said hoarfrost is an urban myth that came out of the bush. I was responding to him.


Quote:
It's still frost. You are attempting to make it out to be something it is not. It still adheres to surfaces just like any other frost...because it is frost.

Well then describe the adhering mechanism for two solids that come into contact. Also if all frost is the same then why use a different term for it?


Quote:
The reference that we were asking for was the one that says it doesn't adhere to surfaces.

Without spending a lot of time on finding better texts (and I hate to use this reference because they misused the term sublimation):

"Hoar frost occurs when a sub-zero surface comes into contact with moist air. The water vapour in the air turns directly into ice by sublimation, forming a white crystalline ice coating which can normally be brushed off."

https://www.skybrary.aero/index.php/Hoar_Frost


Quote:
If you want to use the cold wing scenario, a cold-soaked fuel tank can make frost deposit directly on the fuel tank area even when there's no frost in the environment otherwise and the air temperature is well above freezing. It's the same mechanism. It adheres and no, it doesn't just brush off.

WHAT?? Completely different mechanism. The cold fuel cools the warm air around the wing to the saturation point and water vapor condenses into water where it attaches to the surface which is below freezing so the condensed water then freezes into ice or frost adhering to the wing.


"there's no frost in the environment" this sentence just doesn't make any sense. There's always some water vapor in the air.


Quote:
Due to the low sun and cold temps, hoarfrost often forms on our car windows in the winter time, even in the daytime, so we spend a few minutes scraping it off. Forms on the metal body as well. Sometimes it's damn near impossible to get off without heating the car from the inside to at least partially melt it. If it behaved as you claim, I could just blow it off with my breath.

That's not hoarfrost. See above. The windshield radiates to cold space on a clear night thereby cooling it below ambient temperatures. The air immediately above the window is cooled, saturates, and water condenses onto the window where it then freezes, adhering to the windshield. Ambient air temperature can be above freezing.


Quote:
The only situations I've observed in Alaska where ice does not adhere is dry snow when it's below freezing

Exactly!


Quote:
I've never seen a form of frost that can be brushed or polished off. I've seen plenty of people try...but it's still there after they attempt to brush/polish it.

I've seen it and it done many times. I've even watched it sublimate away once we started taxi'ing in a Piper. It is very common in drier climates.


Quote:
You seem to be implying the "polish smooth" thing about it...
I have no idea what you mean by this. The whole point of this argument is if the hoarfrost in the pictures that FAASTER posted would prevent the wing from providing adequate lift. Read any aircraft icing source and they will describe that ice either roughens the surface or deforms the shape of the airfoil enough that it disrupts and detaches the airflow from the wing. I made the point, actually several points, that 1) the hoarfrost is not rough (enough) and those pictures clearly show surface features under the frost such that it's probably 1/32" thick or less and 2) other surface imperfections are much more significant than the thin, light, and conforming layer of hoarfrost yet the FAA hypocritically ignores these.


So just to be clear, you are saying that the wing in the photos posted is unsafe and will not generate adequate lift?


Look up turbulators.
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Old 09-17-2020, 09:18 AM   #73  
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Originally Posted by Ace66 View Post
No, not all frost goes directly to the solid state:

Window frost

Window frost (also called fern frost or ice flowers) forms when a glass pane is exposed to very cold air on the outside and warmer, moderately moist air on the inside. If the pane is not a good insulator (for example, if it is a single pane window), water vapour condenses on the glass forming frost patterns. With very low temperatures outside, frost can appear on the bottom of the window even with double pane energy efficient windows because the air convection between two panes of glass ensures that the bottom part of the glazing unit is colder than the top part. On unheated motor vehicles the frost will usually form on the outside surface of the glass first. The glass surface influences the shape of crystals, so imperfections, scratches, or dust can modify the way ice nucleates. The patterns in window frost form a fractal with a fractal dimension greater than one but less than two. This is a consequence of the nucleation process being constrained to unfold in two dimensions, unlike a snowflake which is shaped by a similar process but forms in three dimensions and has a fractal dimension greater than two.[8]

Well then describe the adhering mechanism for two solids that come into contact. Also if all frost is the same then why use a different term for it?
It's the same as any other frost that forms when the temp is below zero, such as adhering to my windshield, the wing of an aircraft, etc. Small imperfections are like mountains and valleys on a microscopic level and the ice forms in those and creates a structure that is bounded by multiple anchor points, like a mountaineering cam. The same way the frost formed on that picture of the log that I took. I can "break" the crystals relatively easily, but they are adhering at the base and they do not brush off. The log is more of a macro scale. If what you claim is true, I'd have no use for a an ice-scraper most of the winter, since it remains below freezing and is clear most of the time. I'd be able to just "blow off" the ice crystals from my windshield, but we both know that's not real.

You have to realize the logic fail here. Ice, such as clear or rime ice is also a solid, so even though it's a liquid and then freezes, it too wouldn't have any adhering after forming, according to your theory, since both would then be "solids".

Quote:
"Hoar frost occurs when a sub-zero surface comes into contact with moist air. The water vapour in the air turns directly into ice by sublimation, forming a white crystalline ice coating which can normally be brushed off."

https://www.skybrary.aero/index.php/Hoar_Frost
Hoarfrost, by multiple references, is the extent to which the frost grows in high humidity. Yes, it does go directly from a gas to a solid, but so does "normal frost" when the air temp is below zero, it's only the extent of the ice crystal propagation that is referred to as "hoarfrost". Again, if what you were claiming is true, there's be no way that hoarfrost can form on fences, signs, etc., because it would "fall off", since those are solids too.

Quote:
WHAT?? Completely different mechanism. The cold fuel cools the warm air around the wing to the saturation point and water vapor condenses into water where it attaches to the surface which is below freezing so the condensed water then freezes into ice or frost adhering to the wing.
It still happens in cold temps when there's enough moisture in the air.

Quote:
That's not hoarfrost. See above. The windshield radiates to cold space on a clear night thereby cooling it below ambient temperatures. The air immediately above the window is cooled, saturates, and water condenses onto the window where it then freezes, adhering to the windshield. Ambient air temperature can be above freezing.
100% wrong. It's below freezing the entire time, the water does not come out as liquid. Maybe you are referring to some warmer location where the air temp is above freezing and the cold surface causes the water to condense first. That's not what I'm talking about. I can take some pictures in a few months if it helps you.

Quote:
So just to be clear, you are saying that the wing in the photos posted is unsafe and will not generate adequate lift?
Doesn't matter, the regulation is what it is. You can probably take off with a lot of ice adhering to the wing and leading edges in many situations. Doesn't change that it's illegal.
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Old 09-18-2020, 12:38 AM   #74  
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Yes, zerozero said hoarfrost is an urban myth that came out of the bush. I was responding to him.
Well this little disagreement has certainly made mountains out of mole hills! Or maybe it would be more accurate to say glaciers out of frost crystals.

Look I don't have the time for this little exercise, but I do want to clear up this one misunderstanding. I was not saying hoarfrost is myth. On the contrary, hoarfrost is a very real phenomenon.

What I was trying to say was your comments about the hoarfrost simply blowing off the wing and therefore (it sounded like) there's no need to deice, reminded me of the bush pilot myths that I heard when I was out there.

The fact is, any wing contamination *should* be addressed in order to depart with the "clean wing" as described by JamesNoBrakes.

That's all I got.
Safe flights.
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