Watched several videos about dewpoint (lectures, physics and etc.) and the your explanation (through aviation optics) was the one that really made me understand the concept! thank you.
I don’t get the part where “the aircraft radiates heat away and so it cools down below the ambient air”. I think that’s wrong. I believe the correct explanation is that the aircraft which was at a much colder temperature when in flight has relatively quickly been brought into a warmer (high humidity) environment and so while the external surface of the landed aircraft may be at TOAT temperature (39F) momentarily after landing, the internal structure is far cooler (e.g. 20F) as it hasn’t had a chance to equalize with the outside air on ground. This produces a temperature gradient between the innermost/coldest part of the aircraft (at 20F) and the ambient air (at 39F) and if this gradient is sharp enough I.e. the aircraft has descended relatively quickly to warmer/high humidity air after a long cruise flight in colder air, it will quickly cool the skin back down to at or below freezing (32F) while the aircrafts sits unpowered in the parking area. The reason why horizontal surfaces ice up first is because that’s where the fuel tanks are and the fuel at 20F will take much longer to equalize to outside air therefore the wings have a greater potential for such icing. On the other hand, the air inside the cabin is usually at much higher temperatures (e.g.70F) and so the gradient is usually reversed on most vertical surfaces (non-wing surfaces, more correctly) and so there’s zero possibility of icing at those areas. Bottom line is if the ambient is assuredly above freezing, there is absolutely no way frozen moisture will stay frozen on the skin given enough time has elapsed for the aircraft reach equilibrium with its surrounding. Furthermore, if the ambient is above dew point temperature, even the thawed out moisture will evaporate back into the air after enough time has elapsed. I made a point to write this comment because I found the explanation as well the conclusion that in such occurrences, one has to wait until morning for higher TOAT before they could depart quite misleading. Depending on amount of fuel and the coldest temp. the aircraft has seen in cruise, the wait would mostly likely be less than a couple of hours for skin frost to disappear.
It also happens on cars. I get frost on my car (parked) when it gets down to 40F (36F dew point) but only on the roof and not the doors. The roof radiates heat away into the sky but the doors receive heat from walls and objects.
I also did not understood it initially, yet the video is right, its radiation the one creating the frost, remember objects can cool down on 3 ways, 1. Conduction, 2. Convection, 3. Radiation, you can look up the first 2 but basically its due to molecule to molecule heat transference, on the other hand Radiation cooling happens due to electromagnetic radiation, what this means is that any surface of the plane that is looking into the sky (specially on a cloudless night) is releasing thermal energy trough electromagnetic radiation into the space, this type of radiation usually wont interfere with surrounding water or air molecules ( it depends on the wavelength, with what type of material will interact this electromagnetic waves) but it will go directly into space, so to make it easier: The upper surface of the wings are radiating heat trough electromagnetic radiation into space and only the space (not interacting with the surrounding air) so they cool down yet they absorb trough conduction temperature from the surrounding air and as a result the surrounding air cools down even more dropping its already low temperature below freezing temp and creates that frost over the wing, if the plane is left outside long enough the process will have time for it to create frost If the air is moving or the plane its moved to a new location the process fo cooling the surrounding air will start again, so technically I believe the guy on the video could have started to fly and not worry about ice over the wings as the process would have been interrupted (however by regulation you must never operate an airplane that hast snow or ice on its surfaces) yet if the air is so cold at ground level is really likely it would be even colder up at flight level so unless my plane has anti ice systems I would not consider it. If you want more info search Radiative cooling in wikipedia. (sorry for the bad English I am not a native English speaking person)
The glass of water analogy was great, thank you for this
Watched several videos about dewpoint (lectures, physics and etc.) and the your explanation (through aviation optics) was the one that really made me understand the concept! thank you.
Glad it was helpful!
This was so simple and easy to understand. I love it.
On the ground use Fahrenheit, feet and inches, aloft, use centigrade and metric. English when communication. I was told years ago.
Excellent explanation.👍
I don’t get the part where “the aircraft radiates heat away and so it cools down below the ambient air”. I think that’s wrong.
I believe the correct explanation is that the aircraft which was at a much colder temperature when in flight has relatively quickly been brought into a warmer (high humidity) environment and so while the external surface of the landed aircraft may be at TOAT temperature (39F) momentarily after landing, the internal structure is far cooler (e.g. 20F) as it hasn’t had a chance to equalize with the outside air on ground. This produces a temperature gradient between the innermost/coldest part of the aircraft (at 20F) and the ambient air (at 39F) and if this gradient is sharp enough I.e. the aircraft has descended relatively quickly to warmer/high humidity air after a long cruise flight in colder air, it will quickly cool the skin back down to at or below freezing (32F) while the aircrafts sits unpowered in the parking area.
The reason why horizontal surfaces ice up first is because that’s where the fuel tanks are and the fuel at 20F will take much longer to equalize to outside air therefore the wings have a greater potential for such icing. On the other hand, the air inside the cabin is usually at much higher temperatures (e.g.70F) and so the gradient is usually reversed on most vertical surfaces (non-wing surfaces, more correctly) and so there’s zero possibility of icing at those areas.
Bottom line is if the ambient is assuredly above freezing, there is absolutely no way frozen moisture will stay frozen on the skin given enough time has elapsed for the aircraft reach equilibrium with its surrounding. Furthermore, if the ambient is above dew point temperature, even the thawed out moisture will evaporate back into the air after enough time has elapsed. I made a point to write this comment because I found the explanation as well the conclusion that in such occurrences, one has to wait until morning for higher TOAT before they could depart quite misleading. Depending on amount of fuel and the coldest temp. the aircraft has seen in cruise, the wait would mostly likely be less than a couple of hours for skin frost to disappear.
It also happens on cars. I get frost on my car (parked) when it gets down to 40F (36F dew point) but only on the roof and not the doors. The roof radiates heat away into the sky but the doors receive heat from walls and objects.
I also did not understood it initially, yet the video is right, its radiation the one creating the frost, remember objects can cool down on 3 ways, 1. Conduction, 2. Convection, 3. Radiation, you can look up the first 2 but basically its due to molecule to molecule heat transference, on the other hand Radiation cooling happens due to electromagnetic radiation, what this means is that any surface of the plane that is looking into the sky (specially on a cloudless night) is releasing thermal energy trough electromagnetic radiation into the space, this type of radiation usually wont interfere with surrounding water or air molecules ( it depends on the wavelength, with what type of material will interact this electromagnetic waves) but it will go directly into space, so to make it easier:
The upper surface of the wings are radiating heat trough electromagnetic radiation into space and only the space (not interacting with the surrounding air) so they cool down yet they absorb trough conduction temperature from the surrounding air and as a result the surrounding air cools down even more dropping its already low temperature below freezing temp and creates that frost over the wing, if the plane is left outside long enough the process will have time for it to create frost
If the air is moving or the plane its moved to a new location the process fo cooling the surrounding air will start again, so technically I believe the guy on the video could have started to fly and not worry about ice over the wings as the process would have been interrupted (however by regulation you must never operate an airplane that hast snow or ice on its surfaces) yet if the air is so cold at ground level is really likely it would be even colder up at flight level so unless my plane has anti ice systems I would not consider it.
If you want more info search Radiative cooling in wikipedia.
(sorry for the bad English I am not a native English speaking person)
The beat explanation on UA-cam
Thank you for kind reply and feedback.
Thank you
Thank you!
great video it should have more views thanks
thank you never under stood tiil now
Hey it's John from fly8ma.com!
He does a great job!
You get frost on a telescope and the reason you radiate so much is because it's radiating into space which is 3 degrees above absolute zero.
Moore Jose Davis Karen Williams George
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Please America, got metric and Celsius.
Why would you use farenheit when talking about aviation? Pleease go metric.