Temp and frost-- fly/ no fly
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Join Date: Mar 2001
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Temp and frost-- fly/ no fly
Hey gang....
I'm just in the door after treking all the way to my local airport, and now back again without flying!
I was going to do a night flight (C172) nothing fancy, wx was perfect, and the freezing level was given at 3,000ft... perfect I thought because I planned my little trip at 1,500ft.
Checking the ATIS the temperature was +3deg C, but there was frost slowly starting to form on the wings of the a/c.
I rang the met man and asked the actual temp, thinking the ATIS was a bit dated, and he said "the air temp is +3 at the moment, but its just below freezing at the moment on the ground"
I wasn't entirelly sure what he ment, but the OAT guage in the a/c on the ground indicated 0deg exactly....
I was a bit confused with the whole thing, but the fact was I could start to scrape frost off the upper level of the wings so I decided to play safe and call off the night flight.
If anybody could help me out with this temperature situation I would really appreciate it.
I guess I should of said the dewpoint was +1deg also.
Cheers
I'm just in the door after treking all the way to my local airport, and now back again without flying!
I was going to do a night flight (C172) nothing fancy, wx was perfect, and the freezing level was given at 3,000ft... perfect I thought because I planned my little trip at 1,500ft.
Checking the ATIS the temperature was +3deg C, but there was frost slowly starting to form on the wings of the a/c.
I rang the met man and asked the actual temp, thinking the ATIS was a bit dated, and he said "the air temp is +3 at the moment, but its just below freezing at the moment on the ground"
I wasn't entirelly sure what he ment, but the OAT guage in the a/c on the ground indicated 0deg exactly....
I was a bit confused with the whole thing, but the fact was I could start to scrape frost off the upper level of the wings so I decided to play safe and call off the night flight.
If anybody could help me out with this temperature situation I would really appreciate it.
I guess I should of said the dewpoint was +1deg also.
Cheers
Join Date: Feb 2004
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Hi,
Based on my current winter flight lessons with my CFI in Toronto, Canada. We had been getting snow and frost on the wings for the days that we flew, primarily during the day. Our procedure is that we can fly as long as the temp doesnt go below -20C.
While we do the walk around, if we see a good coat of frost, we usually try to scrape it, althought, 100% of the time, we would have it deiced before we go up.
Frost dont usually occur in-flight (BUT DONT QUOTE ME ON IT!), based on my beginner's knowledge in aviation weather, but I DO know that icing condition CAN occur if you were in the clouds that contain SUPERCOOLED droplets, which CAN exist at night. Then the ice will from around the wings and contaminate the surface.
Tom
Based on my current winter flight lessons with my CFI in Toronto, Canada. We had been getting snow and frost on the wings for the days that we flew, primarily during the day. Our procedure is that we can fly as long as the temp doesnt go below -20C.
While we do the walk around, if we see a good coat of frost, we usually try to scrape it, althought, 100% of the time, we would have it deiced before we go up.
Frost dont usually occur in-flight (BUT DONT QUOTE ME ON IT!), based on my beginner's knowledge in aviation weather, but I DO know that icing condition CAN occur if you were in the clouds that contain SUPERCOOLED droplets, which CAN exist at night. Then the ice will from around the wings and contaminate the surface.
Tom
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If frost was forming on the wings, it may be that the fuel was at a temperature below freezing because of a previous flight above the freezing level.
Bottom line - do not go fly with any frost or ice on the aircraft (unless the tech log approves otherwise - sometimes allowable under the wing fuel tanks). I heard some years ago that a layer of frost on the wing of a Cessna to the thickness of fine sandpapaer could, if in a critical spot, reduce the aerodynamic efficiency of the wing by up to 60%!
Bottom line - do not go fly with any frost or ice on the aircraft (unless the tech log approves otherwise - sometimes allowable under the wing fuel tanks). I heard some years ago that a layer of frost on the wing of a Cessna to the thickness of fine sandpapaer could, if in a critical spot, reduce the aerodynamic efficiency of the wing by up to 60%!
Join Date: Aug 2001
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Obviously the conditions on/around the aeroplane where not the same as in the met man's measuring box.
It is a good idea to be very aware of the risk of freezing as soon as the temperature drops below +5 degrees C.
Good call not to go flying, as Airbedane says the reduction in lift and increase in drag is huge despite the benign appearances of 'a bit of ice'
Ice is one of those things which commands a lot of 'respect' of those who have been in the mire as a result of it.
FD
It is a good idea to be very aware of the risk of freezing as soon as the temperature drops below +5 degrees C.
Good call not to go flying, as Airbedane says the reduction in lift and increase in drag is huge despite the benign appearances of 'a bit of ice'
Ice is one of those things which commands a lot of 'respect' of those who have been in the mire as a result of it.
FD
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Flying when the freezing level is at or near your planned altitude is not a problem in itself - ice will only form if there is moisture too, so if you stay out of rain and/or cloud you are okay. If this wasn't the case there would be very little VFR flying in winter.
As for frost on the plane, it will form whenever the temperature and dewpoint approach zero. The weight of the frost is minimal but it increases drag and disruptes the airflow over the wing. How big a problem this is depends on the type of wing. Laminar flow wings are more adversely affected than the kind of wing you have on a 172. Ideally the frost should be removed by warming up the plane (in a hangar) or applying de-icing fluid. There is a recent discussion on pprune about de-icing fluid.
At very low temperatures (-20C and lower) you'll find various other problems which tend to disappear as things warm up: Instruments "sticking", switch contacts frozen, bare hands to cold to operate the yoke, etc. At these temperatures you'd want the airplane indoors overnight or a mains electricty engine bay warmer.
As for frost on the plane, it will form whenever the temperature and dewpoint approach zero. The weight of the frost is minimal but it increases drag and disruptes the airflow over the wing. How big a problem this is depends on the type of wing. Laminar flow wings are more adversely affected than the kind of wing you have on a 172. Ideally the frost should be removed by warming up the plane (in a hangar) or applying de-icing fluid. There is a recent discussion on pprune about de-icing fluid.
At very low temperatures (-20C and lower) you'll find various other problems which tend to disappear as things warm up: Instruments "sticking", switch contacts frozen, bare hands to cold to operate the yoke, etc. At these temperatures you'd want the airplane indoors overnight or a mains electricty engine bay warmer.
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genius 747
On a properly equipped airfield, the met man can give you both air and surface temp. The surface temp is more aligned to the needs of airfield ops for surface anti-icing. Ice alert systems will also predict where the surface and air temps are heading.
Ice on aircraft has been published, known about and killing people as far back as the 1930's - and still people question its effect on aerodynamic lift. I saw the result once - don't wish to witness it again.
Also, bear in mind the effect on vis when temp and due point come close to mirroring one another at certain times of the year and in calm conditions. (In the UK anyway).
You have to weigh up the facts that present themselves.
On a properly equipped airfield, the met man can give you both air and surface temp. The surface temp is more aligned to the needs of airfield ops for surface anti-icing. Ice alert systems will also predict where the surface and air temps are heading.
Ice on aircraft has been published, known about and killing people as far back as the 1930's - and still people question its effect on aerodynamic lift. I saw the result once - don't wish to witness it again.
Also, bear in mind the effect on vis when temp and due point come close to mirroring one another at certain times of the year and in calm conditions. (In the UK anyway).
You have to weigh up the facts that present themselves.
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I rang the met man and asked the actual temp, thinking the ATIS was a bit dated, and he said "the air temp is +3 at the moment, but its just below freezing at the moment on the ground"
I wasn't entirelly sure what he ment...
If anybody could help me out with this temperature situation I would really appreciate it.
I wasn't entirelly sure what he ment...
If anybody could help me out with this temperature situation I would really appreciate it.
At night the ground will cool (by radiation) quicker that the air above it. This means that the even on nights when the air temp say only goes down to 1-2 degrees you can still get a "ground frost".
This leads to other effects, such a small "inversion layer" in the air temperature near the ground as the ground cools the air directly above it (by conduction). This can form a fog layer in mornings when the air above the ground has been cooled far enough below the dew point.
So going back to your situation, the met office measures air temp inside a slotted box about 4-5 foot off the ground. I haven't heard of the official way of measuring ground temperature, but some else I'm sure can help. Thus, I guess what is happening is that the ground, and your aircraft are cooling quicker than the air above them. Thus your getting ice on the a/c and the OAT (positioned with an inch or so of your aircraft) is reading lower than the official air temp.
As I said, all of the above is based on my old memories of geography lessons, so I am happy to be corrected. But if true, I guess you could have de-iced and gone flying if you have wanted to.
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down&out pretty much sums up in the first three paragraphs why you saw ice on the ground when the temp was forecast as +3
What you have to also consider is that the dew point being so close to actual temperature suggests the air was close to saturation. If the air aloft had cooled any further during your trip, you may have encountered visible moisture at some point which is not what you want and could have caused you all sorts of problems.
What you have to also consider is that the dew point being so close to actual temperature suggests the air was close to saturation. If the air aloft had cooled any further during your trip, you may have encountered visible moisture at some point which is not what you want and could have caused you all sorts of problems.
