Flying in snow
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From: In the boot of my car!
Pace,
You seem convinced that snow cannot stick to an airframe. Ever heard of pack snow?
You seem convinced that snow cannot stick to an airframe. Ever heard of pack snow?
Pace
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From: Wandering the FIR and cyberspace often at highly unsociable times
??? explain?
Here's one place it's discussed: Aircraft icing
And another:
HELICOPTER OPERATIONS IN WINTER
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From: In the boot of my car!
ShyTorque
This is pasted from your example article. I repeat Snow in its pure form will NOT cause icing on an aircraft. Please read the section I posted on the composition and creation of SNOW.
A snow flake is composed of DRY ice and as such cannot cause icing unless it is melted back ino liquid at which point it is no longer snow.
Again read the snippet I highlighted concerning sleet.
Supercooled water droplets or water droplets containing ice particles will cause icing if the temperature is correct for icing but that is NOT SNOW.
It will be the water droplets not the ice paricles contained that will freeze and stick not the ice particles on their own. Without visible moisture NO icing.
For airframe icing to occur there has to be visible moisture and freezing or sub freezing temperatures its as simple as that.
While I agree with the principals of your example article I do not agree with some of their terminology.
I have flown in Snow many times and never once had an icing problem with SNOW in its true sense.
I hope this makes sense ! God this is hard work
Pace
The prerequisites for airframe icing are:
The aircraft must be flying through visible supercooled liquid, i.e. cloud, rain or drizzle
The airframe temperature, at the point where the liquid strikes the surface, must be sub-zero.
The aircraft must be flying through visible supercooled liquid, i.e. cloud, rain or drizzle
The airframe temperature, at the point where the liquid strikes the surface, must be sub-zero.
A snow flake is composed of DRY ice and as such cannot cause icing unless it is melted back ino liquid at which point it is no longer snow.
Again read the snippet I highlighted concerning sleet.
Supercooled water droplets or water droplets containing ice particles will cause icing if the temperature is correct for icing but that is NOT SNOW.
It will be the water droplets not the ice paricles contained that will freeze and stick not the ice particles on their own. Without visible moisture NO icing.
For airframe icing to occur there has to be visible moisture and freezing or sub freezing temperatures its as simple as that.
While I agree with the principals of your example article I do not agree with some of their terminology.
I have flown in Snow many times and never once had an icing problem with SNOW in its true sense.
I hope this makes sense ! God this is hard work
Pace
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From: UK
I don't think I believe the assertion that:
"wet mushy snow, which is a mixture of snow crystals and supercooled raindrops, will form pack snow on the aircraft"
Surely "wet mushy snow" occurs when snow partially melts. Doesn't the fact that the snow is melting indicate above-freezing temperatures, in which case the airframe is probably above freezing too?
"wet mushy snow, which is a mixture of snow crystals and supercooled raindrops, will form pack snow on the aircraft"
Surely "wet mushy snow" occurs when snow partially melts. Doesn't the fact that the snow is melting indicate above-freezing temperatures, in which case the airframe is probably above freezing too?
Avoid imitations
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From: Wandering the FIR and cyberspace often at highly unsociable times
Pace, why make extra hard work of it by posting twice for emphasis?
I'm not talking about dry white snowflakes building up on the wings, which I think you seem to assume. Flying in wet, sticky snow can result in a build up on any stagnation point. It can block an air intake filter housing or in the case of turbine helicopters, cause a slug of wetness to drop into an intake, causing a sudden flameout. It can also build on the stagnation point of the leading edge of a wing or other aerofoil.
The helicopter type I used to operate / instruct had a twenty minute limit on operations in snow with an in-flight visibility of 400 metres or less. We had external mirrors aimed at the engine intakes for this very reason.
Snow builds on cars whilst they are being driven, too - I'm sure you've noticed. Why should aircraft be different?
I'm not talking about dry white snowflakes building up on the wings, which I think you seem to assume. Flying in wet, sticky snow can result in a build up on any stagnation point. It can block an air intake filter housing or in the case of turbine helicopters, cause a slug of wetness to drop into an intake, causing a sudden flameout. It can also build on the stagnation point of the leading edge of a wing or other aerofoil.
The helicopter type I used to operate / instruct had a twenty minute limit on operations in snow with an in-flight visibility of 400 metres or less. We had external mirrors aimed at the engine intakes for this very reason.
Snow builds on cars whilst they are being driven, too - I'm sure you've noticed. Why should aircraft be different?
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From: In the boot of my car!
ShyTorque rectified the double posting sorry about that.
Snow will block any aperture on the airframe if it cannot pass through or has no where to go. A fine grille could cause that an open engine inlet no because the flakes blow through and melt.
On most clean airframes there will not be any areas which will block their passage.
The problem with a car is that its speed envelope will vary from zero to maybe 100 mph.
In snow it speed will probably vary from zero to 30 mph and be varying between that range.
ie not enough airflow at times to blow the flakes away.
As with any snow accumualtion there is a difference between the surface temperature and sub temperatures of the accumulated snow so accumulated snow will vary.
You can walk on snow where the sub layers have melted refrozen and had fresh accumulations on top.
The car is not a good comparison. If you taxied an aircraft on the ground in heavy snow at varying speeds from zero to 30 mph in heavy snow yes you would get the snow settling on the airframe but not at a constant 120 kts +
Pace
Snow will block any aperture on the airframe if it cannot pass through or has no where to go. A fine grille could cause that an open engine inlet no because the flakes blow through and melt.
On most clean airframes there will not be any areas which will block their passage.
The problem with a car is that its speed envelope will vary from zero to maybe 100 mph.
In snow it speed will probably vary from zero to 30 mph and be varying between that range.
ie not enough airflow at times to blow the flakes away.
As with any snow accumualtion there is a difference between the surface temperature and sub temperatures of the accumulated snow so accumulated snow will vary.
You can walk on snow where the sub layers have melted refrozen and had fresh accumulations on top.
The car is not a good comparison. If you taxied an aircraft on the ground in heavy snow at varying speeds from zero to 30 mph in heavy snow yes you would get the snow settling on the airframe but not at a constant 120 kts +
Pace
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From: 59°45'36N 10°27'59E
I have removed blocks of wet snow from both wingroot cabin air intakes on a C172 once, so I know that it builds up there at least.
Now, I was in a big hurry to land just prior, the showers turned to be a bit more intense than i anticipated. (Was just in doing TGL in the circuit)
Now, I was in a big hurry to land just prior, the showers turned to be a bit more intense than i anticipated. (Was just in doing TGL in the circuit)
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From: In the boot of my car!
But what about an airframe flying at 40 to 60 kts?
I cannot give you an exact speed where there is enough air passing over an object to stop a snowflake from settling. In a car you may come to a stop at a road junction in which case the flakes will settle. They land on the car. There maybe heat coming from the engine at a standstill allowing the snow to melt and then the liquid to freeze on accelerating.
There is no such thing as sticky snow. That implies some sort of glue or stickyness which allows it to attach to objects.
True snow is dry and frozen so cannot attach to a frozen surface. Only visible moisture combined with freezing temperatures can attach.
Pace
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From: In the boot of my car!
M609
I dont have a problem with that. If the flakes cannot blow through or the inlet is not heating then yes they will block that aperture.
You should not have a problem with engine cooling inlets unless there was some fine mesh grille over the opening.
Pace
I have removed blocks of wet snow from both wingroot cabin air intakes on a C172 once, so I know that it builds up there at least.
You should not have a problem with engine cooling inlets unless there was some fine mesh grille over the opening.
Pace
Last edited by Pace; 5th February 2009 at 16:36.
Avoid imitations
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From: Wandering the FIR and cyberspace often at highly unsociable times
Bookworm, supercooled water droplets can exist alongside snowflakes. Does that help your understanding? If not, believe what you will, I wish you luck and hope you safely enjoy your cold weather flying in the future. I'm not going to argue the academics or semantics about whether it's academic still snow now or is it academic ice stuck to my aircraft because I know from other discussions here that written debate often can't change a long time fixed belief derived from reading.
A while ago I took part in similar discussion, about carb icing and the possible effects of the use of partial carb heating, other "experienced" pilots couldn't understand the concept that it might be counterproductive not to use FULL heat. One person in particular hadn't realised that fuel evaporation could cause a temperature drop of 20 Celsius in the venturi and believed it was all down to the Bernoulli effect. He's probably still unconvinced.
During another more recent discussion, at least one "experienced" poster said it wasn't possible for helicopters to suddenly cause a highly localised visibility reduction to the point where IMC conditions existed. Until the moderator posted a video showing exactly what I was talking about. He hadn't experienced those weather conditions himself and posted that it therefore couldn't happen...
My own practical experience tells me that some over-generalisations have been stated, especially where operations close to freezing temperatures are concerned. Colder arctic (drier) temperatures can be less dangerous than than those just above or just below freezing, such as in UK of late.
I joined in this debate because I felt concerned that an inexperienced pilot might read what has been posted and assume that falling snow is of little consequence to his winter flight, other than from a reduction in visibility.
I'm not a met expert, only a pilot of some 32 years professional experience, including military winter operations in weather conditions close to (and sometimes unfortunately in) snow and icing conditions. These days, flying an IFR capable aircraft without an icing clearance, I have to draw on my practical experience to keep it safe all year round, while getting the job done whenever possible. Especially as someone previously told the aircraft owner he was buying an all-weather aircraft.
I hope my input has balanced the debate somewhat, others can decide for themselves.
A while ago I took part in similar discussion, about carb icing and the possible effects of the use of partial carb heating, other "experienced" pilots couldn't understand the concept that it might be counterproductive not to use FULL heat. One person in particular hadn't realised that fuel evaporation could cause a temperature drop of 20 Celsius in the venturi and believed it was all down to the Bernoulli effect. He's probably still unconvinced.
During another more recent discussion, at least one "experienced" poster said it wasn't possible for helicopters to suddenly cause a highly localised visibility reduction to the point where IMC conditions existed. Until the moderator posted a video showing exactly what I was talking about. He hadn't experienced those weather conditions himself and posted that it therefore couldn't happen...
My own practical experience tells me that some over-generalisations have been stated, especially where operations close to freezing temperatures are concerned. Colder arctic (drier) temperatures can be less dangerous than than those just above or just below freezing, such as in UK of late.
I joined in this debate because I felt concerned that an inexperienced pilot might read what has been posted and assume that falling snow is of little consequence to his winter flight, other than from a reduction in visibility.
I'm not a met expert, only a pilot of some 32 years professional experience, including military winter operations in weather conditions close to (and sometimes unfortunately in) snow and icing conditions. These days, flying an IFR capable aircraft without an icing clearance, I have to draw on my practical experience to keep it safe all year round, while getting the job done whenever possible. Especially as someone previously told the aircraft owner he was buying an all-weather aircraft.
I hope my input has balanced the debate somewhat, others can decide for themselves.
Last edited by ShyTorque; 5th February 2009 at 16:47. Reason: A few typos and some tidying of grammar and prose.
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From: In the boot of my car!
ShyTorque
This conversation was about snow and whether snow in its true form can stick to an aircraft.
Naturally flying in any conditions where there is visible " moisture" and temperatures conducive to icing in an aircraft which is not Ice capable is asking for trouble, but that advice is valid if there is NO snow.
It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.
Snow and sleet are both dramatic visual indications of ice in the sky but the danger is not the formed ice but the moisture that can turn to ice. It is the moisture which is not so visually dramatic which is the silent killer.
For that reason it is important to understand the physics of icing
The answer to "can pure SNOW in its true form which is a dry frozen and complex structure cause an icing problem?" then the Answer is NO.
Can flying in conditions where there is visible moisture and freezing conditions whether snow is present or not cause icing? YES.
Is snow indicative of icing conditions? Maybe Maybe not.
Pace
This conversation was about snow and whether snow in its true form can stick to an aircraft.
Naturally flying in any conditions where there is visible " moisture" and temperatures conducive to icing in an aircraft which is not Ice capable is asking for trouble, but that advice is valid if there is NO snow.
It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.
Snow and sleet are both dramatic visual indications of ice in the sky but the danger is not the formed ice but the moisture that can turn to ice. It is the moisture which is not so visually dramatic which is the silent killer.
For that reason it is important to understand the physics of icing
The answer to "can pure SNOW in its true form which is a dry frozen and complex structure cause an icing problem?" then the Answer is NO.
Can flying in conditions where there is visible moisture and freezing conditions whether snow is present or not cause icing? YES.
Is snow indicative of icing conditions? Maybe Maybe not.
Pace
Last edited by Pace; 5th February 2009 at 18:06.
Hovering AND talking
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From: Propping up bars in the Lands of D H Lawrence and Bishop Bonner
Originally Posted by Pace
This conversation was about snow and whether snow in its true form can stick to an aircraft.
The answer to "can pure SNOW in its true form which is a dry frozen and complex structure cause an icing problem?" then the Answer is NO.
Whilst you are scientifically correct, "pure" snow is not that common so a semantic arguement based on theoretical molecular structure and is no real help or guidance in real life.
It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.
but the danger is not the formed ice but the moisture that can turn to ice.
Cheers
Whirls
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From: UK
Bookworm, supercooled water droplets can exist alongside snowflakes. Does that help your understanding? If not, believe what you will, I wish you luck and hope you safely enjoy your cold weather flying in the future.
I would be the first to acknowledge that practical experience trumps simplistic science, and I do not undervalue your input, ShyTorque, here or elsewhere. But I do think that understanding the science of weather can help us manage risk better and keep us safe. Some of that is about understanding why some aspects of weather pose less of a hazard than one might naively expect.
Avoid imitations
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From: Wandering the FIR and cyberspace often at highly unsociable times
ShyTorque
This conversation was about snow and whether snow in its true form can stick to an aircraft.
Naturally flying in any conditions where there is visible " moisture" and temperatures conducive to icing in an aircraft which is not Ice capable is asking for trouble, but that advice is valid if there is NO snow.
It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.
This conversation was about snow and whether snow in its true form can stick to an aircraft.
Naturally flying in any conditions where there is visible " moisture" and temperatures conducive to icing in an aircraft which is not Ice capable is asking for trouble, but that advice is valid if there is NO snow.
It is equally dangerous to imply to inexperienced pilots that because its not snowing or sleeting that all is ok.
This quote didn't help:
Do not believe the reason the airports closed. The real reason was the UK pilots believed the stuff may stick to their aircraft turning their planes into giant snowballs streaking through the skies never to be seen again. The runways were set aside exclusively for Father Christmas to practice his touch and goes ready for next Christmas.
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From: In the boot of my car!
Whirly
In the context we are talking about formed ice is NOT a danger and I am not talking about ice forming on your airframe We are talking about snow, ice pellets ie hail (Oh yes that would be a danger but not in the context of icing on the wings)
So please enlighten me to how formed ice is a danger to aircraft icing as I would like to know?
Not that common! you are joking I hope? i have flown through tons of the stuff a lot at night.
Snow is snow in about 20 types if it melts its no longer snow. Sleet is not snow.
Pace
Formed ice not a danger? I hope you don't believe that.
We are talking about snow, ice pellets ie hail (Oh yes that would be a danger but not in the context of icing on the wings)So please enlighten me to how formed ice is a danger to aircraft icing as I would like to know?
Whilst you are scientifically correct, "pure" snow is not that common so a semantic arguement based on theoretical molecular structure and is no real help or guidance in real life.
Snow is snow in about 20 types if it melts its no longer snow. Sleet is not snow.
Pace
Last edited by Pace; 5th February 2009 at 19:53.
Avoid imitations
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From: Wandering the FIR and cyberspace often at highly unsociable times
But I do think that understanding the science of weather can help us manage risk better and keep us safe. Some of that is about understanding why some aspects of weather pose less of a hazard than one might naively expect.
Hovering AND talking
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From: Propping up bars in the Lands of D H Lawrence and Bishop Bonner
In the context we are talking about
I am not talking about ice forming on your airframe
We are talking about snow
Formed ice on rotor blades is a danger.
Cheers
Whirls
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From: In the boot of my car!
Whirls okay
Snow is formed ice it is a structure of very pretty forms and shapes all created out of dry ice. Melt it and the poor thing collapses into a very unnatractive drop of water But hey ho its not the frozen stuff I fear its its the liquid stuff which can freeze.
Pace
Snow is formed ice it is a structure of very pretty forms and shapes all created out of dry ice. Melt it and the poor thing collapses into a very unnatractive drop of water
But hey ho its not the frozen stuff I fear its its the liquid stuff which can freeze.Pace
Avoid imitations
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From: Wandering the FIR and cyberspace often at highly unsociable times
Pace, we all know that sarcasm is the lowest form of wit but an attempt to patronise and be sarcastic at the same time doesn't reinforce your argument one bit. As you said early on, you are being over pedantic and by doing so you do not give a practical answer to the poster's original question.
I won't post further here but I've sent the original poster my honest advice with regard to his original question by other means.
I won't post further here but I've sent the original poster my honest advice with regard to his original question by other means.