frost on the wing

On Dec 24, 9:28*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.

Any thoughts? *Have you seen this before?

Jose


What happens is that the wing and fuel get super cooled in flight at
extremely low temps. If the wings and fuel are cold soaked enough any
moisture contacting the wing may form frozen contamination. This
forms on the upper surfaces after landing especially if you have alot
of fuel remaining. Certain times of the year you will see this alot on
the bottom surfaces of the wing where the fuel tanks are.
F Baum

If the wings and fuel are cold soaked enough any
moisture contacting the wing may form frozen contamination. This
forms on the upper surfaces after landing especially if you have alot
of fuel remaining.

What would prevent this from happening in flight? (n.b. in my case the ambient flight temps were just below freezing - radiative cooling may have lowered the wing temp =some= more, but a =lot= more?)

Jose
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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. 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.

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

Jose wrote in
:

If the wings and fuel are cold soaked enough any
moisture contacting the wing may form frozen contamination. This
forms on the upper surfaces after landing especially if you have alot
of fuel remaining.

What would prevent this from happening in flight? (n.b. in my case
the ambient flight temps were just below freezing - radiative cooling
may have lowered the wing temp =some= more, but a =lot= more?)


Well, nothng if it's wet enough outside, but it's unlikely you're going to
get a low altitude airplane and it's fuel cold enough to do it in flight.
It happens often on airliners if they've been at altitude for extended
periods and they get th efuel down to low temps and then descend into
moisture.


Bertie