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Date: Wed, 19 Jul 2006 11:11:40 -0400
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From: "Hamid A. Wasti" <hwasti@starband.net>
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Subject: Re: [LML] Re: VistaNav
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Marvin Kaye wrote:
> Posted for "Tom Gourley" <tom.gourley@verizon.net>:
>
> The Inertial
> Navigation Unit, one of the two boxes that makes up a complete system, 
> has
> reasonable specs; up to 24,000 feet and operating temperature from 32F to
> 105F.
I would hardly call that reasonable.  And 32F is the "standard 
atmosphere" at about 7,500 feet.  105F is essentially 40C.  It is way 
too low for real life use.  Temperatures in excess of 80C behind the 
panel are well documented.  On a "normal" warm day of 35C, you can see 
temperatures well in excess to 45C in locations where you would normally 
install a box.  Places like Phoenix routinely get over 45C in the shade 
during the summer.  Just to put things in perspective, a box with those 
temperature specifications would not even get past the front door to 
talk to an automotive company, let alone any aviation company.  

> Does this mean the tablet, or Mobile Computing
> Platform as it's called, will stop working above 10,000 feet.  I doubt it.
Wrong answer.  Hard drives count on an air cushion to keep them from 
touching the spinning disk.  The damping of the air resistance against 
lateral movement of the head is also taken into consideration when 
designing the closed loop  control for positioning the head.  As you get 
high, the air thins and both the cushion as well as the damping 
decrease  The result is failure to seek if you are lucky, a hard crash 
if you are unlucky.  This is not just theory, but is well documented.  
Also, the denser the drive, the more susceptible it is to altitude 
related problems.

The second issue is cooling.  Cooling of the CPU.  Colling of the power 
supplies.  Cooling of the graphics chip.  Cooling of the backlight.

Of course, you can ignore all of that and boldly press on -- many do.  
Maybe you will get lucky and things will work for you, maybe not.

Regards,

Hamid