Bob Gardner wrote:
On the ground, the pressure inside the airplane and outside of the airplane
are the same...why would you expect the needle to wiggle?

Bob Gardner

wrote in message
oups.com...
I was preparing to fly a cessna 172SP the other day and as I usually
do I pulled the alt.static expecting a small wiggle in the gauges. And
got nothing. This was the first time I i got no response from the
gauges. I was told by somebody at the front desk this was common and
that many of the 172's show no movement at all. But.. if this is so..
how can I be certain the alt.static would work when I needed it.


Thanks in advance.

The act of moving the valve causes a slight, transitory pressure
change.

That causes the VSI to wiggle one way when you open it then the other
when you close it.

On some airplanes the prop wash will cause a very slight differntial
between the inside and outside which will also cause a slight
wiggle in the VSI.

--
Jim Pennino

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