alt. static.

wrote:

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.


On the ground, there doesn't always have to be a significant difference
between cabin air pressure and outside pressure. I'd recommend trying the
check in flight. If you don't see any difference there, then you've got a
leak in the static system.

John Galban=====N4BQ (PA28-180)

--
Message posted via http://www.aviationkb.com

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

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.


On the ground, there doesn't always have to be a significant difference
between cabin air pressure and outside pressure. I'd recommend trying the
check in flight. If you don't see any difference there, then you've got a
leak in the static system.

Correct me if I'm wrong here, but isn't a preflight supposed to be done
before you take off?

And one more time...

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

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation

--
Jim Pennino

Remove .spam.sux to reply.

wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Seriously, I suspect that the 172 you're talking about probably does have a
static leak into the cabin. If you want to verify that in order to get it
fixed, flipping to the alt static at speed will be most convincing to
maintenance personnel. Another way to check for a cabin static leak is to
open a window (if allowed) in flight. If your VSI, airspeed and altimeter
needles jump, you've got a leak in the cabin.

On the ground, some aircraft do not experience a perceptable indication due
to the location of the exterior static port.

John Galban=====N4BQ (PA28-180)

--
Message posted via http://www.aviationkb.com

On Nov 1, 12:58 am, wrote:
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.

I have seen some airplanes show a small wiggle, and some that don't
when the static port is turned on or off. There is no easy way to
positively verify that your alternate static is working. If you are up
to it, you could suck on the static port and ask someone to verify
whether the VSI is showing a climb. Then repeat with the alt static
open. The latter should not show a climb. Or get a suction for this
purpose. Just a thought. I have never done it this way.

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Every CFI I had while a student said to do it and every 172 I've ever
flown does it.

Specifically, at the beginning of the preflight walk around, after
ensuring the master is off, pull the alternate static control out, then
shove it in to make sure it is off; the VSI should wiggle.

That's while standing in the open door.

Seriously, I suspect that the 172 you're talking about probably does have a
static leak into the cabin.

I am not the one that posed the original question nor have I flown a 172
newer than a P model.

If you want to verify that in order to get it
fixed, flipping to the alt static at speed will be most convincing to
maintenance personnel. Another way to check for a cabin static leak is to
open a window (if allowed) in flight. If your VSI, airspeed and altimeter
needles jump, you've got a leak in the cabin.

On the ground, some aircraft do not experience a perceptable indication due
to the location of the exterior static port.

Maybe, but the original poster was talking specifically about a 172.

--
Jim Pennino

Remove .spam.sux to reply.

On Sat, 03 Nov 2007 00:05:02 GMT, wrote:

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Every CFI I had while a student said to do it and every 172 I've ever
flown does it.

Specifically, at the beginning of the preflight walk around, after
ensuring the master is off, pull the alternate static control out, then
shove it in to make sure it is off; the VSI should wiggle.

That's while standing in the open door.

Same for every 172 and 182 I've flown. Isn't the action of actuating
the flaper in the selector box (or t or whatever it is that it's
moving) creating a little pressure wave which is what makes the
needles move?

Peter Clark wrote:
On Sat, 03 Nov 2007 00:05:02 GMT, wrote:

JGalban via AviationKB.com u32749@uwe wrote:
wrote:

begin speculation

Now it could be that after some serial number Cessna changed something
and the later models don't do that, and that would be OK as long as
I have something at least quasi offical to tell me that.

end speculation


Do you have something quasi official that tells you the VSI must wiggle
when alt static is checked on the ground? If so, then your question would
appear to be answered.

Every CFI I had while a student said to do it and every 172 I've ever
flown does it.

Specifically, at the beginning of the preflight walk around, after
ensuring the master is off, pull the alternate static control out, then
shove it in to make sure it is off; the VSI should wiggle.

That's while standing in the open door.

Same for every 172 and 182 I've flown. Isn't the action of actuating
the flaper in the selector box (or t or whatever it is that it's
moving) creating a little pressure wave which is what makes the
needles move?

That's what I was told and that if the systems working, the needle
bounces one way when opened and the other when closed.

--
Jim Pennino

Remove .spam.sux to reply.

On Nov 2, 3:55 pm, Andrew Sarangan wrote:
On Nov 1, 12:58 am, wrote:

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.

I have seen some airplanes show a small wiggle, and some that don't
when the static port is turned on or off. There is no easy way to
positively verify that your alternate static is working. If you are up
to it, you could suck on the static port and ask someone to verify
whether the VSI is showing a climb. Then repeat with the alt static
open. The latter should not show a climb. Or get a suction for this
purpose. Just a thought. I have never done it this way.

To clarify i have flown - rented - this aircraft a lot and it always
wiggled. The aircraft is a 172SP.

I would not cancel a VFR flight in the area for the lack of
alt.static, but as my CFI said - I asked him this question too - IFR
would be a different story.

On 2007-11-02 15:55:56 -0700, Andrew Sarangan said:

On Nov 1, 12:58 am, wrote:
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.

I have seen some airplanes show a small wiggle, and some that don't
when the static port is turned on or off. There is no easy way to
positively verify that your alternate static is working. If you are up
to it, you could suck on the static port and ask someone to verify
whether the VSI is showing a climb. Then repeat with the alt static
open. The latter should not show a climb. Or get a suction for this
purpose. Just a thought. I have never done it this way.

You don't want to, either. I have had avionics guys tell me that this
can damage the instruments.
--
Waddling Eagle
World Famous Flight Instructor

On Sat, 03 Nov 2007 15:05:03 GMT, wrote:


That's what I was told and that if the systems working, the needle
bounces one way when opened and the other when closed.


Every airplane that I've flown that's so equipped did exactly that.