frost on the wing

On Dec 24, 8:28 am, Jose wrote:


Which got me thinking - maybe the FAA isn't so crazy after all. If frost can form while the plane is just sitting there, why could it not form while the plane is flying? (yeah, there's some frictional heating, but we could lower the temp a bit more, no?) And if frost isn't such a good thing to have on takeoff, it's probably not so good in flight either.

The frost on your wings was most certainly formed after your landed.
It happened to me a few times on some very clear cold days. I fly a
low wing Grumman and I could see the frost started to form as I slowly
taxi back to the ramp.

If you depart in such condition, it would be a good idea to spray
propylene glycol (RV antifreeze, not the automobile antifreeze) on
your wings and horizontal stablizers before taxi out, after you clear
out all the frost.

I've iced up to the ailerons in a Warrier, cold fuel can play a part
here too.

Bush

On Mon, 24 Dec 2007 16:28:33 GMT, Jose
wrote:

The other day I went flying, pretty close to the shortest day of the year, to preserve night currency. I took advantage of a day that wasn't brutally cold - in fact it was above freezing, so I didn't need preheat or thermal underwear. It was good to get in the air after several months of not flying hardly at all (we had the longest, most beautiful fall but I was stuck indoors doing two shows at the same time). I had to taxi over a bit of an ice berm in front of the wheels, but it wasn't a problem, and the pavement was wet from the melting ice (we had several inches of ice storm a week or so ago which is still around).

By the time I got in the air, I was happy and all was well with the world. After doing some night full stop landings, I followed I-84 up to Beacon and back just to "go somewhere" and then came home. By now temperatures were just below freezing, but it was clear and so I didn't give it much consideration.

Landed without incident, braking was good (and was also reported good by aircraft before me), and I taxiied to the ramp, a relatively unfamiliar part of the airport since we moved the airplanes. The airplane seemed to be sliding a bit, as if there was ice on the pavement. Well, of course there was; the wet pavement had frozen in the interim. I was afraid of that, and this meant that putting the plane away would not be as easy as taking it out. After a struggle I did manage to get it pushed back over the ice berms (pulling up on the wing while pushing back helped, as did pulling with the tiedown ropes when I got close enough). But when I was pretty much done, I noticed there was frost on the wings, which hadn't been there before.

Which got me thinking - maybe the FAA isn't so crazy after all. If frost can form while the plane is just sitting there, why could it not form while the plane is flying? (yeah, there's some frictional heating, but we could lower the temp a bit more, no?) And if frost isn't such a good thing to have on takeoff, it's probably not so good in flight either.

Any thoughts? Have you seen this before?

Jose

On 12/24/2007 11:28:36 AM, Jose wrote:

But when I was pretty much done, I noticed there was frost on the wings,
which hadn't been there before.

I have experienced this a few times. Two memorable times were once after
landing at Niagara Falls airport and once after landing in Plattsburgh, NY.
In these two cases it was after dark, the sky was clear, and the temperatures
were very cold (perhaps around 0 to -10 degrees F). In each situation the
aircraft's wings and horizontal stabilizer frosted over within minutes of
landing.

--
Peter

On Dec 24, 11:07 am, quietguy wrote:
On Dec 24, 11:32 am, Jose wrote:

What would prevent this from happening in flight?

Sublimation. The airflow around the wing evaporates deposited ice
crystals fast enough to keep visible frost from forming unless the
relative humidity is near 100% (i.e., when there's visible moisture).
Then, depending mainly on the droplet size, you'll get either rime
(frost by another name) or clear icing.

Frost forms when the metal radiates its heat into the clear
sky faster than the surrounding air, so that it gets cooler than the
air and the moisture condenses on it in the form of frost. In flight,
the air moving around the wing keeps it at the same temperature as the
wing and frost won't form. Other forms of ice will, in the right
conditions, but they're not frost. They're impact ice, supercooled
water droplets that freeze when they hit the wing and anything else in
the way. Frost forms directly from vapour to solid without going
through the liquid phase.

Takes a hell of a wind to
cause rapid-enough sublimation, though: I've seen parked airplanes get
frosty even when gusts were in the forties.

That's hoarfrost, related to impact icing. Not sublimation. It's
the same supercooled water droplets found in ice fog.

Dan