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Epidemic of cracked windshields in KDEN, explanation unknown



 
 
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  #11  
Old February 18th 07, 01:23 AM posted to rec.aviation.piloting,rec.travel.air
Roy Smith
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Posts: 478
Default Epidemic of cracked windshields in KDEN, explanation unknown

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.
  #12  
Old February 18th 07, 01:29 AM posted to rec.aviation.piloting,rec.travel.air
Matt Whiting
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Posts: 2,232
Default 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.


It can't be as cold as the jets routinely see above 30,000 feet. I
suspect the wind was carrying stones or ice chunks or something like
that which cracked the windshields.


Matt
  #13  
Old February 18th 07, 01:36 AM posted to rec.aviation.piloting,rec.travel.air
Kev
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Posts: 368
Default Epidemic of cracked windshields in KDEN, explanation unknown

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

  #14  
Old February 18th 07, 01:38 AM posted to rec.aviation.piloting,rec.travel.air
James Robinson
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Posts: 180
Default Epidemic of cracked windshields in KDEN, explanation unknown

Matt Whiting 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.


It can't be as cold as the jets routinely see above 30,000 feet. I
suspect the wind was carrying stones or ice chunks or something like
that which cracked the windshields.


I suspect the the crews turned on the electric windshield heating without
proper warmup when it was very cold, and the cracks resulted from thermal
stresses in the windows. The cracks were reported to have happened in the
air, where flying rocks would be rare, and not on the ground.
  #15  
Old February 18th 07, 02:16 AM posted to rec.aviation.piloting,rec.travel.air
Mike Young
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Posts: 54
Default Epidemic of cracked windshields in KDEN, explanation unknown

"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.


  #16  
Old February 18th 07, 04:05 AM posted to rec.aviation.piloting,rec.travel.air
Mxsmanic
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Posts: 9,169
Default Epidemic of cracked windshields in KDEN, explanation unknown

Bob Moore writes:

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.....


It sounds logical. Many models of aircraft were affected, though (and in fact
Boeing wasn't mentioned--if a Boeing windshield cracks, there's a _real_
problem). Mostly those Brazilian planes and some others. Most were on the
ground, not in the air.

--
Transpose mxsmanic and gmail to reach me by e-mail.
  #17  
Old February 18th 07, 04:05 AM posted to rec.aviation.piloting,rec.travel.air
Mxsmanic
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Posts: 9,169
Default Epidemic of cracked windshields in KDEN, explanation unknown

Blanche writes:

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


Wind chill applies only to people, not things.

--
Transpose mxsmanic and gmail to reach me by e-mail.
  #18  
Old February 18th 07, 04:06 AM posted to rec.aviation.piloting,rec.travel.air
Matt Barrow[_3_]
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Posts: 65
Default Epidemic of cracked windshields in KDEN, explanation unknown

"Jim Macklin" wrote in message
news
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.


Single digits below zero. Nothing.

Certainly not "rocks blowing around".


| 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.
|


  #19  
Old February 18th 07, 04:14 AM posted to rec.aviation.piloting,rec.travel.air
Matt Barrow[_3_]
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Posts: 65
Default Epidemic of cracked windshields in KDEN, explanation unknown

"Kev" wrote in message
ups.com...
On Feb 17, 5:14 pm, "Jim Macklin"



On the other hand, they mentioned 100 mph ground winds,


Who is "they"?

and that means
flying rocks to me.


As those are borderline tornado winds, it's more like regular debris.

--
Matt Barrow
Performance Homes, LLC

  #20  
Old February 18th 07, 04:18 AM posted to rec.aviation.piloting,rec.travel.air
Matt Barrow[_3_]
external usenet poster
 
Posts: 65
Default Epidemic of cracked windshields in KDEN, explanation unknown

"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.




 




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