alt. static.

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.

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.

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

Remove .spam.sux to reply.

On Nov 1, 8:55 am, "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


Are you indicating it won't? i.e. are you saying in your experience it
does not wiggle?

I expect it to move because that is what I was taught. And I have
flown a lot of these and have never seen it not "wiggle".

I am interested in how I know the knob works. Is looking for the
wiggle a reliable way to tell if the alt. static system is going to
function when I need it. If not how do I know. Should the item have
been squawked or simply noted as an observation.

wrote:

On Nov 1, 8:55 am, "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



Are you indicating it won't? i.e. are you saying in your experience it
does not wiggle?

I expect it to move because that is what I was taught. And I have
flown a lot of these and have never seen it not "wiggle".

I am interested in how I know the knob works. Is looking for the
wiggle a reliable way to tell if the alt. static system is going to
function when I need it. If not how do I know. Should the item have
been squawked or simply noted as an observation.




In the Cessna's I've seen the static port is near the pilots knees. If
this is the case in the plane you're talking about take a look under the
panel at the connection to this port. If you can reach it from the
pilots seat then all you have to do is pull it off the fitting and you
have alternate air.

Newps wrote in
:

In the Cessna's I've seen the static port is near the pilots knees. If
this is the case in the plane you're talking about take a look under the
panel at the connection to this port. If you can reach it from the
pilots seat then all you have to do is pull it off the fitting and you
have alternate air.

Alternatively, break the glass on the VSI.

Judah wrote:
Newps wrote in
:


In the Cessna's I've seen the static port is near the pilots knees. If
this is the case in the plane you're talking about take a look under the
panel at the connection to this port. If you can reach it from the
pilots seat then all you have to do is pull it off the fitting and you
have alternate air.


Alternatively, break the glass on the VSI.



The smart pilot finds where the pitot line runs instead for two reasons.
It's harder than hell to break the glass and second that costs money
if you actually can break it.

Judah wrote:
Newps wrote in
:

In the Cessna's I've seen the static port is near the pilots knees. If
this is the case in the plane you're talking about take a look under the
panel at the connection to this port. If you can reach it from the
pilots seat then all you have to do is pull it off the fitting and you
have alternate air.

Alternatively, break the glass on the VSI.

Neither of which seem to me to be very good preflight procedures, which
is what the question is about.

--
Jim Pennino

Remove .spam.sux to reply.

wrote in news
Neither of which seem to me to be very good preflight procedures, which
is what the question is about.

Do you intend to imply that if your alternatic air source does not make the
VSI wiggle, you would cancel your flight failing a suitable pre-flight
procedure?

Judah wrote:
wrote in news

Neither of which seem to me to be very good preflight procedures, which
is what the question is about.

Do you intend to imply that if your alternatic air source does not make the
VSI wiggle, you would cancel your flight failing a suitable pre-flight
procedure?

No, I'm outright saying that pulling hoses or breaking the glass on
the VSI isn't a viable preflight procedure.

And since I've never seen a 172 where the VSI didn't wiggle when I
turned the alternate on and off, I would want to know why it didn't
before I flew it.

--
Jim Pennino

Remove .spam.sux to reply.