How fast does the skin of the airplane cool to surrounding temperatures?

wrote:
writes:
On a clear night the skin temperature can go BELOW the air
temperature due to the radiation losses into space.


Tony wrote:
Dan, it's not an important point, but from the physics/theromdynamics
side of the issue, the top surface of the wing is really at risk of
radiational cooling. The wing's leading edge's shape would allow
convective warming, as the warmer air in contact with the surface would
cool and flow downward.

And that's where we see frost forming: on top of the wings,
fuselage and stabilizer.

Yea, same here. Often we'll get lots of frost on the top of the plane,
almost never on the bottom. I wasn't sure if the difference was temp or
moisture.

-Robert

Yea, same here. Often we'll get lots of frost on the top of the plane,
almost never on the bottom. I wasn't sure if the difference was temp or
moisture.

The bottom is subject to radiation heating from the pavement.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

"Jose" wrote in message
. net...
Yea, same here. Often we'll get lots of frost on the top of the plane,
almost never on the bottom. I wasn't sure if the difference was temp or
moisture.

The bottom is subject to radiation heating from the pavement.

Jose

Zactly - radiation depends on what the surface is exposed to. I park my
mini-van next to a big pine tree in the driveway - the tree side is clear in
the morning- it "see's" the tree. The other windows are frosted over (even
if the overnight low is still a bit above freezing) - they are exposed to
the sky. It's a real problem with telescopes too. Since they are pointed
directly at the sky (on clear nights) the objective lens cools off rapidly
and will fog up. Look up "telescope heater".

The earth surfaces cool first through radiation, which, in turn, cools the
air (which is reasonably "transparent" to a lot of wavelengths). That's what
makes clear nights colder than cloudy nights - more heat loss to space via
radiation. And having the air cooled by the surface of the earth is what
causes surface winds to often die down at sundown - you get a layer of cold,
heavy, air that just sits there under the warmer air that is moving around
the high and low pressure areas.

During the daytime, of course, radiation from the sun warms the surface,
which then warms the air. The nice thing about that is that it is the
mechinism that triggers the thermals that keep glider pilots aloft (dragging
it back to aviation content, eh?).

But to get back to the orignial post - just ask the guy in the next hanger,
he/she ought to know if they have been in the area a few years, right?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote:

But to get back to the orignial post - just ask the guy in the next hanger,
he/she ought to know if they have been in the area a few years, right?

In the several months since starting my hangar contract at that airport I
have yet to meet any of the fellow hangar lessees. Either they don't fly a
lot or my arrival/departure timing is out of sync with theirs. Most likely
the latter.

--
Peter