Yesterday, I was flying along the tops of a broken layer and picked up
a thin layer of frost/ice on the wings with a thin triangle-shaped
pattern to the frost. This was a new one to me.

Conditions:
Plane: Cherokee 180
Altimeter 30.05
Broken layer @ 4000MSL (~3000AGL)
OAT = -5degF
Clear above the 040 BKN layer
Time was 10am, which put the sun almost directly behind the plane.

The leading edge of the wing was clear (free of frost) from the
leading edge to approximately 8 inches back (chordwise).

At the 8-inch chord mark, several frost outlines in a triangle shape
were present. The frost outline started as a point, and tapered back
evenly on either side, slowly 'enlarging' the frost pattern so that it
looked like a triangle pointed towards the leading edge. There were
several of these patterns on the wing, one every few feet (spanwise).
The frost patterns were not aligned with the rivets.

The frost triangles were about 1-2 feet long and 6 inches wide.

The OAT gauge/windshield did not accumulate any frost/ice.

Explanations? Similar occurrences?

-Nathan

It is probably due to structure on your airplane being colder than the air.
The triangles are probably reinforcements or doublers under the skin. I get
this a lot on the MU-2 after landing when the fuel is at -40C and frost
forms on the underside of the wing where the fuel contacts the skin.

Mike
MU-2


"Nathan Young" > wrote in message
...
> Yesterday, I was flying along the tops of a broken layer and picked up
> a thin layer of frost/ice on the wings with a thin triangle-shaped
> pattern to the frost. This was a new one to me.
>
> Conditions:
> Plane: Cherokee 180
> Altimeter 30.05
> Broken layer @ 4000MSL (~3000AGL)
> OAT = -5degF
> Clear above the 040 BKN layer
> Time was 10am, which put the sun almost directly behind the plane.
>
> The leading edge of the wing was clear (free of frost) from the
> leading edge to approximately 8 inches back (chordwise).
>
> At the 8-inch chord mark, several frost outlines in a triangle shape
> were present. The frost outline started as a point, and tapered back
> evenly on either side, slowly 'enlarging' the frost pattern so that it
> looked like a triangle pointed towards the leading edge. There were
> several of these patterns on the wing, one every few feet (spanwise).
> The frost patterns were not aligned with the rivets.
>
> The frost triangles were about 1-2 feet long and 6 inches wide.
>
> The OAT gauge/windshield did not accumulate any frost/ice.
>
> Explanations? Similar occurrences?
>
> -Nathan
>

On 2005-12-06, Mike Rapoport > wrote:
> this a lot on the MU-2 after landing when the fuel is at -40C and frost
> forms on the underside of the wing where the fuel contacts the skin.

What, Prist can't fix that?! ;-)

--
Ben Jackson
>
http://www.ben.com/

An advertisement for Sci-Fi Channel's new mini-series?

On 07 Dec 2005 00:36:05 GMT, Blanche > wrote:

>An advertisement for Sci-Fi Channel's new mini-series?

Well, this did happen in the Minneapolis area, so perhaps it had
something to do with the light pillars mentioned a day ago. :-)

In article >,
Nathan Young > wrote:

> On 07 Dec 2005 00:36:05 GMT, Blanche > wrote:
>
> >An advertisement for Sci-Fi Channel's new mini-series?
>
> Well, this did happen in the Minneapolis area, so perhaps it had
> something to do with the light pillars mentioned a day ago. :-)

I could throw in some more than usually uninformed speculation (even for
this group . . . ) about a random dot of frost forming, causing the
airflow to spread out laterally just a bit; gases cool when they expand
(happens in nozzles and many types of refrigerators); result is more
frost forming in the region just behind the dot; and the
forward-pointing triangle grows toward the rear of the plane.

Fits the available data presented thus far, and stranger things happen
in gas and liquid flows all the time -- but I have no idea if anything
like this is really happening here.

"AES" > wrote in message
...
> I could throw in some more than usually uninformed speculation (even for
> this group . . . ) about a random dot of frost forming, causing the
> airflow to spread out laterally just a bit [...]

That was the theory I came up with too. That should be enough to cause you
concern for whether you're actually correct. :)

(I didn't post it, because it seemed too outlandish, even for me :) ).

"AES" > wrote in message ...
> In article >,
> Nathan Young > wrote:
>
>> On 07 Dec 2005 00:36:05 GMT, Blanche > wrote:
>>
>> >An advertisement for Sci-Fi Channel's new mini-series?
>>
>> Well, this did happen in the Minneapolis area, so perhaps it had
>> something to do with the light pillars mentioned a day ago. :-)
>
> I could throw in some more than usually uninformed speculation (even for
> this group . . . ) about a random dot of frost forming, causing the
> airflow to spread out laterally just a bit; gases cool when they expand
> (happens in nozzles and many types of refrigerators); result is more
> frost forming in the region just behind the dot; and the
> forward-pointing triangle grows toward the rear of the plane.
>
> Fits the available data presented thus far, and stranger things happen
> in gas and liquid flows all the time -- but I have no idea if anything
> like this is really happening here.

Yes, maybe that is the area where the boundary layer was breaking from laminar flow to turbulent flow. It may be a new
way to figure out where to place the vortex generators...

On Tue, 06 Dec 2005 15:52:16 GMT, "Mike Rapoport"
> wrote:

>It is probably due to structure on your airplane being colder than the air.
>The triangles are probably reinforcements or doublers under the skin.

I will have to ask my A&P. I am fairly certain that on a Cherokee,
the inner wing is much simpler than that... Ie ribs with the outer
wing skin riveted to them.

On Tue, 06 Dec 2005 21:16:17 -0800, AES > wrote:

>In article >,
> Nathan Young > wrote:
>
>> On 07 Dec 2005 00:36:05 GMT, Blanche > wrote:
>>
>> >An advertisement for Sci-Fi Channel's new mini-series?
>>
>> Well, this did happen in the Minneapolis area, so perhaps it had
>> something to do with the light pillars mentioned a day ago. :-)
>
>I could throw in some more than usually uninformed speculation (even for
>this group . . . ) about a random dot of frost forming, causing the
>airflow to spread out laterally just a bit; gases cool when they expand
>(happens in nozzles and many types of refrigerators); result is more
>frost forming in the region just behind the dot; and the
>forward-pointing triangle grows toward the rear of the plane.
>
>Fits the available data presented thus far, and stranger things happen
>in gas and liquid flows all the time -- but I have no idea if anything
>like this is really happening here.

This was my best guess as well. I wish had my digital camera with me
- would have been a good one to capture.