Epidemic of cracked windshields in KDEN, explanation unknown

Jim Macklin wrote:

How cold did it get in Denver? Aluminum and plastic have
different contraction rates with cold. Plastic also gets
brittle with cold. Wind flexes wing, which also flexes
fuselages, erg---cracks.

Wow. Really? Isn't it cold at 40000 feet?

On Feb 18, 10:57 pm, Mike Hunt postmaster@localhost wrote:
Jim Macklin wrote:
How cold did it get in Denver? Aluminum and plastic have
different contraction rates with cold. Plastic also gets
brittle with cold. Wind flexes wing, which also flexes
fuselages, erg---cracks.

Wow. Really? Isn't it cold at 40000 feet?

Usually -50.

In article ,
"Matt Barrow" wrote:

"Kev" wrote in message
ups.com...
On Feb 17, 11:15 am, Mxsmanic wrote:
See

http://us.cnn.com/2007/WEATHER/02/17....ap/index.html

So what would cause windshields to crack on many different types of
aircraft
at the same time? It wasn't impact or anything like that. [..]

I don't believe the "wasn't impact" part. I lived in Denver for a
while, and when the winds whip up, stones fly around.

That brought to mind the skit in "Monty Python and the Holy Grail" about
things that will float in water, one of them being small rocks.

But, ducks also float, and they fly. Airplanes also fly. Therefore,
airplanes are small rocks.

"Roy Smith" wrote in message
...
In article ,
"Matt Barrow" wrote:

"Kev" wrote in message
ups.com...
On Feb 17, 11:15 am, Mxsmanic wrote:
See

http://us.cnn.com/2007/WEATHER/02/17....ap/index.html

So what would cause windshields to crack on many different types of
aircraft
at the same time? It wasn't impact or anything like that. [..]

I don't believe the "wasn't impact" part. I lived in Denver for a
while, and when the winds whip up, stones fly around.

That brought to mind the skit in "Monty Python and the Holy Grail" about
things that will float in water, one of them being small rocks.

But, ducks also float, and they fly. Airplanes also fly. Therefore,
airplanes are small rocks.

Tell us how sheep's bladders can be used to predict earthquakes.

Kev writes:

I don't believe the "wasn't impact" part. I lived in Denver for a
while, and when the winds whip up, stones fly around. Cracked
windshields and dust-storm-scarred paint can be quite common out
there.

Maybe. The news article implied that impact wasn't involved.

I was thinking of perhaps some sort of incredibly large temperature
differential, but surely no such differential on the ground could compare with
the differences seen at altitude, so that doesn't seem to explain it, either.

I also understood that most of the cracked windshields occurred on the ground;
only a few involved aircraft that were in the air.

I was under the impression that just about nothing could crack an airliner
windshield short of a transonic brick, but I may be wrong. On smaller
aircraft, I don't know. I suppose they have some sort of regular safety glass
for the windshields, but less fancy than that of high-flying jets (?).

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Mxsmanic wrote
I was under the impression that just about nothing could crack an
airliner windshield short of a transonic brick, but I may be wrong.
On smaller aircraft, I don't know. I suppose they have some sort of
regular safety glass for the windshields, but less fancy than that of
high-flying jets (?).

Of course these jet windshields are heated to provide the middle layer
of plastic with some flexibility to resist shattering in case of a bird
strike at low temps. Should the heating system be turned off and cold-
soaking occur(electrical bus turned off for trouble-shooting perhaps),
Boeing had a procedure for re-heating the windshield at very low temps
to prevent thermal shock from cracking the glass layers. This involved
cycling the power switches ON-OFF at one minute intervals for several
minutes. Sounds to me as if the temps at DEN were quite low and the flight
crews just turned the windshield heat ON and forgot about it.

Just one possibility of course.....

Bob Moore
ATP B-727 B-707
PanAm (retired)

High winds. Low temps (-15F and up) == very cold wind chill factor.

On Feb 17, 7:09 pm, Blanche wrote:
High winds. Low temps (-15F and up) == very cold wind chill factor.

Common misconception. Wind chill only applies to the heat loss of
animals. It does not apply to inanimate objects. The only thing
wind will do to metal, glass, plastic, etc is help cool it faster to
the ambient temperature.

Kev

"Blanche" wrote in message
...
High winds. Low temps (-15F and up) == very cold wind chill factor.

I would think that's still balmy and calm compared to the flight levels. I
dunno why they cracked. The airlines also don't know, and they have been
thinking about this much longer than we have.

Blanche writes:

High winds. Low temps (-15F and up) == very cold wind chill factor.

Wind chill applies only to people, not things.

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