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Old September 6th 16, 05:57 PM posted to rec.aviation.ifr
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Default Altimeter: Hot to cold = look out below?!

On Friday, October 29, 1999 at 12:00:00 AM UTC-7, Mark Kolber wrote:
jcrogin wrote [snip]:

I mean, cold air is more dense than hot air. So if
you fly from hot to cold, why doesn't your altimeter think you're
flying lower, rather than higher? What am I missing?

I've gotten this one wrong a million times until I read this
(highly simplified) explanation in a magazine:

Imagine your airplane riding on top of a cylinder of air.The cylinder
sits on the ground and its sides are rigid, but it's capable of
expanding vertically.

In general, when air (or any gas) warms, it's volume increases. When
it cools, its volume decreases. What effect will that have on the
cylinder your plane is riding on?

Works the same for low pressure -- generally, low pressure means less
weight -- more expansion -- more volume.

______|______ Mark Kolber
\(o)/ Denver, Colorado
o O o
replace "spamaway" with "mlf" for email

Than you for this!!!!!