Frost
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I just looked at my other plane (two planes, but only one hangar here) - it's covered in snow! So I decided to just leave it, and come and read PPRuNe.
I've just got done the recurrent exam on icing and the Cessna Caravan (a type found to be rather sensative to airframe ice). The proper de-ice fluid in a spray can is the way to go. You cannot convince me that sloshing the plane with plain water is a good idea. It is one thing if you fly through soaking condtions, then it freezes - that's a design failing. But, the plane was not designed to resist being sloshed by a pilot on the ground, who was unwilling to use the correct technique to deice a plane. You might get away with it for a while, but the time important things start freezing at altitude, and you have trouble controling the aircraft, the cost saving won't seem worth it any more.
Hands up, all those pilots who have suddenly found that the aircraft they are flying has had a control system completley jam, or found the stall speed is now 15 kts higher than you though it was.
Your effort as a pilot to keep the plane as close as possible to the configuration it was manufactured in, will afford you the least stressful flight. Looking at the plane safely tied down, waiting for another day, is also very low stress....
I've just got done the recurrent exam on icing and the Cessna Caravan (a type found to be rather sensative to airframe ice). The proper de-ice fluid in a spray can is the way to go. You cannot convince me that sloshing the plane with plain water is a good idea. It is one thing if you fly through soaking condtions, then it freezes - that's a design failing. But, the plane was not designed to resist being sloshed by a pilot on the ground, who was unwilling to use the correct technique to deice a plane. You might get away with it for a while, but the time important things start freezing at altitude, and you have trouble controling the aircraft, the cost saving won't seem worth it any more.
Hands up, all those pilots who have suddenly found that the aircraft they are flying has had a control system completley jam, or found the stall speed is now 15 kts higher than you though it was.
Your effort as a pilot to keep the plane as close as possible to the configuration it was manufactured in, will afford you the least stressful flight. Looking at the plane safely tied down, waiting for another day, is also very low stress....
Some interesting stuff here. Does anyone know which if any of the de-icers are safe on fabric? Oh, and the aircraft colour will make a difference to how quickly it warms up in the sun, of course. Used to have a glider with a pale blue wing and a dark blue leading edge, did a fair bit of wave flying so it often got pretty cold. The leading edge ice/frost always melted first. Got a yellow aeroplane now, which lives in a hangar except when we are touring.
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Originally Posted by IO540
I think it is simply because the supercooled water droplets are coming down more or less vertically, unless modified by some local airflow, and then it freezes up to create frost.
That's why one doesn't get frost underneath the wings, IMHO.
That's why one doesn't get frost underneath the wings, IMHO.
The bottom surface radiates to the roughly 0 ground and hence doesn't cool significantly.
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That's why one doesn't get frost underneath the wings, IMHO.
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I would be very surprised to find the E135 collects FROST on the underside, but not top side when left out overnight (I am not considering cases such as having just landed after a good cold soak or in flight icing).
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(I am not considering cases such as having just landed after a good cold soak or in flight icing).
Most airplanes that are "frost" covered can be cleaned with a stiff broom. That is ceratinly what I would try first.
A truely ice covered aircraft should only be dealt with by using a proper heated aircraft deicing fluid or throughly warmed in a heated hangar. I would suggest that homemade deicing solutions should not be used as they can harm the paint or worse can be corrosive enough to damage control surface bearings, hingers, rod ends etc, or when they pool inside the sheet metal structure.
The bottom line however, is no amount of ice on a flying or control surface is acceptable.
A truely ice covered aircraft should only be dealt with by using a proper heated aircraft deicing fluid or throughly warmed in a heated hangar. I would suggest that homemade deicing solutions should not be used as they can harm the paint or worse can be corrosive enough to damage control surface bearings, hingers, rod ends etc, or when they pool inside the sheet metal structure.
The bottom line however, is no amount of ice on a flying or control surface is acceptable.
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Robert, clearly deicing is currently a popular pastime. Of the on-line retail suppliers I checked for Killfrost or other deicing fluid all were out of stock waiting for a new supply. The only fluid I could see available for purchase at the moment was direct from the manufacturer – Killfrost RDF is available in 25 litre barrels at around £150 including transport from their www site http://www.kilfrost.com/online-shop/general-aviation
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No frost to speak of this morning at Redhill. But broken cloud at 900' so flight to Barton cancelled. Light snow up there too.
Thanks for a very interesting and informative thread!
Thanks for a very interesting and informative thread!
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No, Frost forms on the upper surface (normally at night) due to the surface radiating heat to the -265 ish degree black sky. This substantially reduces the skin temperature and it causes water vapour to freeze out of the air.
The bottom surface radiates to the roughly 0 ground and hence doesn't cool significantly.
The bottom surface radiates to the roughly 0 ground and hence doesn't cool significantly.
A thin sheet will not be representative, due to strong thermal conductivity between upside and downside.
Still I'm curious to see what ally you'll be using: légionnaires must slice much thinner than GI's, meseemeth.
Still I'm curious to see what ally you'll be using: légionnaires must slice much thinner than GI's, meseemeth.
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As jan says, the two surfaces must be thermally separate otherwise you just wind up at a plate with the net balance of heating from the ground, cooling to space and convection to the air. Even a plate bent 180 should have enough air gap (and the conduction at the edge will be much more limited than across the front to back.
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Fibreglass glider left out overnight at Aboyne (Deeside Gliding Club). Use of credit cards for removing ice from flying surfaces the usual treatment.
One evening, warmer and a wee drop of rain, so no frost to contend with. Surfaces nice and clean. Bright day, sunshine, lenticular clouds beckoning. Warmly dressed, followed the Pawnee to 2,500' above site, pulled off in lift, worked the wave to 12,000' or thereabouts, when the ailerons declined to move any more. That's interesting, I said to myself. Turned gently with the rudder, that was okay. Airbrakes okay too. Just no aileron function at all.
Decided to descend, gingerly. Below 5,000 they freed up enough to do a safe approach and landing. I consulted with Dave Richardson, who easily diagnosed the problem; the aileron tape, still wet, had frozen. Simple, really.
Main thing, if something seems wrong, don't panic, work with what you've got left. I'm just glad there was no problem with the elevator.....
One evening, warmer and a wee drop of rain, so no frost to contend with. Surfaces nice and clean. Bright day, sunshine, lenticular clouds beckoning. Warmly dressed, followed the Pawnee to 2,500' above site, pulled off in lift, worked the wave to 12,000' or thereabouts, when the ailerons declined to move any more. That's interesting, I said to myself. Turned gently with the rudder, that was okay. Airbrakes okay too. Just no aileron function at all.
Decided to descend, gingerly. Below 5,000 they freed up enough to do a safe approach and landing. I consulted with Dave Richardson, who easily diagnosed the problem; the aileron tape, still wet, had frozen. Simple, really.
Main thing, if something seems wrong, don't panic, work with what you've got left. I'm just glad there was no problem with the elevator.....
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@Mary, that is still a scary story!
@The Science Club: I would love to hear the results of the experiment. Paradoxically, I would expect the upper plate to be warmer, the more ice that formed on it. The latent heat of deposition (vapour to ice) is 720 cal/g, so 1g of ice is enough to raise 3.6kg of Aluminium (Ally?) by 1 deg C. I would still expect the upper plate to be cooler than the lower plate though.
I was just listening to the head of salting and gritting for Leeds. He made the point that the ground temperature is lower than the air temperature. Which I think I learned somewhere. The ground cools the air, and that cool air stays put close to the ground, underneath the warmer air at 4-feet where the official air temperature is measured. So if the wings are radiation cooling, like the ground, they too can be colder than the lowest overnight air temperature.
@The Science Club: I would love to hear the results of the experiment. Paradoxically, I would expect the upper plate to be warmer, the more ice that formed on it. The latent heat of deposition (vapour to ice) is 720 cal/g, so 1g of ice is enough to raise 3.6kg of Aluminium (Ally?) by 1 deg C. I would still expect the upper plate to be cooler than the lower plate though.
I was just listening to the head of salting and gritting for Leeds. He made the point that the ground temperature is lower than the air temperature. Which I think I learned somewhere. The ground cools the air, and that cool air stays put close to the ground, underneath the warmer air at 4-feet where the official air temperature is measured. So if the wings are radiation cooling, like the ground, they too can be colder than the lowest overnight air temperature.
I once spent considerable time scraping off frost between the rivet lines on a C-172 and found that while the a/c did take off, the ravine at the end of the runway was most helpfully placed for building to a higher than book climb speed
If the approved fluids are not immediately available, -40C automotive windshield deicer applied with windshield scrubbing sponge and squeegee should do the job without damage to the paintwork -- but please test first on a small patch and remember that aircraft windshields and windows are especially vulnerable
Once the wing and tail are clean and dry, it does not matter how the result was achieved.
If the approved fluids are not immediately available, -40C automotive windshield deicer applied with windshield scrubbing sponge and squeegee should do the job without damage to the paintwork -- but please test first on a small patch and remember that aircraft windshields and windows are especially vulnerable
Once the wing and tail are clean and dry, it does not matter how the result was achieved.
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As jan says, the two surfaces must be thermally separate otherwise you just wind up at a plate with the net balance of heating from the ground, cooling to space and convection to the air. Even a plate bent 180 should have enough air gap (and the conduction at the edge will be much more limited than across the front to back.
mmflynn
A frost covered 747 in any temp will be deiced (as necessary) with a concentration/mix of de-icing fluid, probably Type II in UK, warmed to about +80C. It could be 50% or more commonly 75% mix of fluid/water to give a better hold over time. The chemicals in the fluid, as you say, substantially reduce the temp at which the water/fluid mix will re-freeze. But that is it's purpose, to stop the applied fluid re-freezing. It is not there to remove the ice in the first place, heat is the primary agent in removing ice/frost.
Type IV fluid is rarely, if ever, used in UK. It isn't necessary and as has been said, can cause more trouble if the excess fluid is allowed to build up in aerodynamically dead areas in hinges or control surfaces. It dries eventually and then when it gets wet again rehydrates and swells up only to refreeze as you climb to lower ambient temps. It has happened on several large a/c.
My point is that a/c size does not matter, the procedure should be well known by all operators and followed to the letter. It saves on messy paperwork.
Anti-icing is used if the forcast is accurate. Can that method be implemented on light a/c or is that too impracticle?
We are removing a little bit of frost on a -2 kind of day , not trying to get a 747 clear of a 6 inch snow covering in Munich. The chemicals substantially reduce the freezing point of water (after all that is how TKS deice works!) so the frost melts even if you have not heated the backpack. The liquid has a reasonable hold over so it doesn't refreeze. However, I take a towel round the aircraft to mop up all the now liquid frost. Clearly a bit impractical on a 747 (unless you have a lot of hostiees!)
Type IV fluid is rarely, if ever, used in UK. It isn't necessary and as has been said, can cause more trouble if the excess fluid is allowed to build up in aerodynamically dead areas in hinges or control surfaces. It dries eventually and then when it gets wet again rehydrates and swells up only to refreeze as you climb to lower ambient temps. It has happened on several large a/c.
My point is that a/c size does not matter, the procedure should be well known by all operators and followed to the letter. It saves on messy paperwork.
Anti-icing is used if the forcast is accurate. Can that method be implemented on light a/c or is that too impracticle?