Altimeter Calibration Height

"Neil Gould" wrote in message
et...
Recently, Steven P. McNicoll posted:

"Neil Gould" wrote in message
et...

Perhaps you misunderstood Jose's example, but I believe he's correct;
while an altimeter senses the pressure at the level of the
insturment, it *indicates* the calibration set by either the shop
(e.g. compensating for the altitude of the installation) or the
pilot via the Kollsman window.


I understood it, I didn't say he was wrong.

Perhaps I misunderstood your response.

Jose stated:
[...] An altimeter indicates whatever it is set to indicate.
[...]

and:
If you don't get an altimeter setting, you will (likely) set the
altimeter so that the hands indicate the airport elevation as
indicated on your charts, even though you and the instrument are a
hundred feet higher.

If you do get an altimeter setting, you'll set it for that. Then the
question becomes (since the altimeter doesn't know that it's in a
tall airplane) whether, at calibration in the shop, it was set to
indicate actual instrument altitude or to indicate something else
(like instrument altitude minus a hundred feet).
[...]

To which you replied:

In other words, an altimeter indicates altitude at the level of the
instrument itself.

How do you reconcile your comment against Jose's statements? Both
statements will only be true under a very limited set of circumstances
that I would think excludes "In other words...".


You snipped part of Jose's message:

"Also, even if the static port and the instrument themselves are separated
in altitude, it would be the instrument altitude's pressure that is sensed,
since the "column of air" is connected, and ends at the instrument."

In other words, an altimeter indicates altitude at the level of the
instrument itself.

You snipped part of Jose's message:

"Also, even if the static port and the instrument themselves are separated
in altitude, it would be the instrument altitude's pressure that is sensed,
since the "column of air" is connected, and ends at the instrument."

In other words, an altimeter indicates altitude at the level of the
instrument itself.

No. Correctly it would be "In other words, an altimeter =senses=
=pressure= at the level of the instrument itself."

Sensing pressure and indicating altitude are two different things.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Jose" wrote in message
t...

No. Correctly it would be "In other words, an altimeter =senses=
=pressure= at the level of the instrument itself."

Sensing pressure and indicating altitude are two different things.


An altimeter senses pressure in order to indicate altitude.

An altimeter senses pressure in order to indicate altitude.

Now we're getting somewhere. The pressure is sensed based on the laws
of physics. The altitude is indicated based on calibration and Kollsman
setting.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Jose" wrote in message
t...
An altimeter senses pressure in order to indicate altitude.

Now we're getting somewhere. The pressure is sensed based on the laws of
physics. The altitude is indicated based on calibration and Kollsman
setting.


Maybe I'm missing something here, but would it simplify to say:

That if you mount an altimeter at the 100' level of a 200' tower,
equiped it with a static tube 100' long,
that the altimeter will read the same regardless if end of the tube,
is stationed at the top or bottom of the tower.

?????

if you mount an altimeter at the 100' level of a 200' tower,
equiped it with a static tube 100' long,
that the altimeter will read the same regardless if end of the tube,
is stationed at the top or bottom of the tower.

That is a mostly true statement. Conditions inside the tube could
differ from ambient conditions, this would engender a teeny (but real)
difference in readings.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Jose" wrote in message
. ..
if you mount an altimeter at the 100' level of a 200' tower,
equiped it with a static tube 100' long,
that the altimeter will read the same regardless if end of the tube,
is stationed at the top or bottom of the tower.

That is a mostly true statement. Conditions inside the tube could differ
from ambient conditions, this would engender a teeny (but real) difference
in readings.

Jose

You mean like pressure loss of the long length or something?

"Maxwell" wrote in message
...

Maybe I'm missing something here, but would it simplify to say:

That if you mount an altimeter at the 100' level of a 200' tower,
equiped it with a static tube 100' long,
that the altimeter will read the same regardless if end of the tube,
is stationed at the top or bottom of the tower.

?????


Why didn't I think of that?

Maxwell wrote:
"Jose" wrote in message
t...
An altimeter senses pressure in order to indicate altitude.
Now we're getting somewhere. The pressure is sensed based on the laws of
physics. The altitude is indicated based on calibration and Kollsman
setting.


Maybe I'm missing something here, but would it simplify to say:

That if you mount an altimeter at the 100' level of a 200' tower,
equiped it with a static tube 100' long,
that the altimeter will read the same regardless if end of the tube,
is stationed at the top or bottom of the tower.

Yes, that is correct. There might be a slight transient as you moved
the tube, but at steady state the location of the tube would not matter.

Matt

"Jose" wrote in message
t...

Now we're getting somewhere. The pressure is sensed based on the laws of
physics. The altitude is indicated based on calibration and Kollsman
setting.


Correct.