Epidemic of cracked windshields in KDEN, explanation unknown

"Tony" wrote in message
oups.com...
Wind chill has everything to do with how fast heat is lost from
someone at body temperature. It's widely held that the old data,
that's 'wind chill', is not a very accurate measure of the effect of
wind on flesh and there's some work going on for a better measure. The
statement the poster made about any heat-generating object is not
quite complete, I'm sure he meant to remind us that it's related to
the surface temperature of the object, or at least the surface
temperatture in no wind conditions.

Fans in your computer are there to move air mass against hot objects
to carry the heat away, they are trying to create 'wind chill' inside
the computer. You can google 'convective heat loss' or 'forced air
cooling' if you want to explore the subject in more depth.

Googling on "wind chill" nets a different set of results. Notice the human
reference in the following from weather.gov:

[[
Specifically, the new WCT index:

a.. Calculates wind speed at an average height of five feet (typical
height of an adult human face) based on readings from the national standard
height of 33 feet (typical height of an anemometer)
b.. Is based on a human face model
c.. Incorporates modern heat transfer theory (heat loss from the body to
its surroundings, during cold and breezy/windy days)
d.. Lowers the calm wind threshold to 3 mph
e.. Uses a consistent standard for skin tissue resistance
f.. Assumes no impact from the sun (i.e., clear night sky).
]]

In rec.aviation.piloting Tony wrote:
Fans in your computer are there to move air mass against hot objects
to carry the heat away, they are trying to create 'wind chill' inside
the computer. You can google 'convective heat loss' or 'forced air
cooling' if you want to explore the subject in more depth.

That's not what wind chill is about. You need to take into account
evaporative cooling, which has a significant effect.

.... Alan
--
Alan Gerber
PP-ASEL
gerber AT panix DOT com

I don't think so.

The windchill temperature is calculated using the following formula:

Windchill (ºF) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Whe T = Air Temperature (F)
V = Wind Speed (mph)
^ = raised to a power (exponential)

Windchill Temperature is only defined for temperatures at or below 50
degrees F and wind speeds above 3 mph. Bright sunshine may increase
the windchill temperature by 10 to 18 degrees F.



On Feb 22, 2:12 am, Alan Gerber wrote:
In rec.aviation.piloting Tony wrote:

Fans in your computer are there to move air mass against hot objects
to carry the heat away, they are trying to create 'wind chill' inside
the computer. You can google 'convective heat loss' or 'forced air
cooling' if you want to explore the subject in more depth.

That's not what wind chill is about. You need to take into account
evaporative cooling, which has a significant effect.

... Alan
--
Alan Gerber
PP-ASEL
gerber AT panix DOT com

I need to retreat a little here. The formula I gave looks to be a
curve fit to an empirical data set, and that data may have been
obtained with evaporative losses as a factor. I seem to remember,
however, the experiments were done observing heat loss from plastic
bottles filled with water, the thickness of the plastic offering more
or less the same thermal impedence as does skin.

So, I hereby extinguish the implied flame.

Sorry about that. Now I'm off to slay more meaningful dragons and save
a maiden or two.

CLEAR!



imperical data ting formay be wrong On Feb 22, 2:20 am, "Tony"
wrote:
I don't think so.

The windchill temperature is calculated using the following formula:

Windchill (ºF) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Whe T = Air Temperature (F)
V = Wind Speed (mph)
^ = raised to a power (exponential)

Windchill Temperature is only defined for temperatures at or below 50
degrees F and wind speeds above 3 mph. Bright sunshine may increase
the windchill temperature by 10 to 18 degrees F.

On Feb 22, 2:12 am, Alan Gerber wrote:



In rec.aviation.piloting Tony wrote:

Fans in your computer are there to move air mass against hot objects
to carry the heat away, they are trying to create 'wind chill' inside
the computer. You can google 'convective heat loss' or 'forced air
cooling' if you want to explore the subject in more depth.

That's not what wind chill is about. You need to take into account
evaporative cooling, which has a significant effect.

... Alan
--
Alan Gerber
PP-ASEL
gerber AT panix DOT com- Hide quoted text -

- Show quoted text -

I think the newsgroup would be interested in this finding.

"Although windborne debris was at first dismissed as a cause for the
14 cracked aircraft windshields last week at Denver International
Airport, investigators now are saying FOD, or foreign-object debris,
was indeed to blame. Microscopic analysis showed fine particles caused
pitting that in turn caused cracking, NTSB investigator Jennifer
Kaiser told the Denver Post. The runways had been sanded during recent
snowstorms, and it's suspected that the winds, gusting up to 48 mph,
drove the fine sand particles into the windshields. The fractures
affected six passenger jets as they were taking off, seven on the
airport surface, and one at 19,000 feet. The NTSB offered no
explanation regarding that high-altitude incident. Also unexplained
was the apparent lack of damage to any aircraft surfaces other than
windscreens. "The only commonality across aircraft type, operator,
location, time and phase of flight was the wind and weather," Kaiser
told the Post.


groupOn Feb 18, 9:27 pm, wrote:
On Feb 17, 5:07 pm, Blanche wrote:

Winds on Thursday & Friday reached over 100 mph in the foothills.
We don't use salt, as a rule, on the roads. Ice slicer and a
combination of fine rocks. Add to this the everyday, run-of-the-mill
rocks and gravel kicked up on the roads, and it's normal to replace
thewindshieldsevery 2-4 years (I'm due this year. Last change
was in 2004). Get these winds, a few hefty rocks, and
a new windshield sooner than expected.

KDEN is surrounded by empty fields (for the most part), which means
lots of "stuff" in the area that is kicked up by the winds.

Boulder is a town just north ofDenver, right at the foothills, which
are steep and abrupt.
Sometime in the late 80s or early 90s, a windstorm from the west blew
out nearly all of the front and back autowindshieldsin a parking
lot. IIRC it wasn't debris, but the wind itself. It gets to howling
there some times.

Probably nothing to do with the current situation, though. I'd have
to think that a wind that strong would also bend the airplanes up a
bit.

Where is Richard Feynman when you need him to explain what the
'experts' can't....

denny

Isn't sanding areas at an airport kind of a bad idea, precisely because sand
could be FOD?

--
Transpose mxsmanic and gmail to reach me by e-mail.