Altimeter Calibration Height

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?


Humidity or moisture content comes most readily to my mind.

Peter

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

The conditions inside the tube are different from the conditions outside
the tube. I expect they'd be very similar, but given a very long, very
insulated tube, which starts out with (say) dry air, followed by the
passage of a moist front, there would be a difference.

Jose
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Right and the altitude indicated has little to do with the altitude of the instrument.

Well, that's a little extreme. They are related like integrals to the
same function: +C

Jose
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"Jose" wrote in message
t...
You mean like pressure loss of the long length or something?

The conditions inside the tube are different from the conditions outside
the tube. I expect they'd be very similar, but given a very long, very
insulated tube, which starts out with (say) dry air, followed by the
passage of a moist front, there would be a difference.


Agreed, and even moisture would be a factor as Peter suggested.

By the tower example I was just trying to verify that the altimeter measured
presssure based on it's location, not the location of the static port, with
the exception of errors caused a longer or shorter length of hose to the
port.

"Neil Gould" wrote in message
t...

You do when you imply that there is a necessary agreement between what the
altimeter senses and what it displays.


What implied that?



Jose listed them in response to an earlier post of yours.


I must have missed that one.



You actually said, "When you tell a pilot "altimeter 3012" the pilot
simply adjusts the *Kollsman setting* to 3012." (emphasis mine).
As we described the same action, this distinction is without a functional
difference.


I think there's a significant functional difference between adjusting the
altimeter setting and adjusting the indicated altitude.

"Matt Whiting" wrote in message
news

Right and the altitude indicated has little to do with the altitude of the
instrument.


Right. That's why changing the altitude of the instrument, as is done by
climbing or descending, has so little effect on the indicated altitude.

Recently, Steven P. McNicoll posted:

"Neil Gould" wrote in message
t...

You do when you imply that there is a necessary agreement between
what the altimeter senses and what it displays.


What implied that?

On 4/2/07, you wrote:
"An altimeter indicates altitude at the level of the instrument itself. "

and, again:
"In other words, an altimeter indicates altitude at the level of the
instrument itself. "

And so forth. That is not necessarily so.

You actually said, "When you tell a pilot "altimeter 3012" the pilot
simply adjusts the *Kollsman setting* to 3012." (emphasis mine).
As we described the same action, this distinction is without a
functional difference.


I think there's a significant functional difference between adjusting
the altimeter setting and adjusting the indicated altitude.

Well, I wrote:
"Consider that when you tell a pilot that the "altimeter is 30.12", the
pilot adjusts the indicated altitude by setting the Kollsman window to
that pressure setting."

The "adjustment" in both cases is to the Kollsman setting. The result is a
change in the displayed altitude. So, what is different is the structure
of the sentence, not the action or intent, unless you think your omission
of the resulting displayed altitude is significant. If so, why do you
think so?

Neil

"Neil Gould" wrote in message
. net...

On 4/2/07, you wrote:
"An altimeter indicates altitude at the level of the instrument itself. "

and, again:
"In other words, an altimeter indicates altitude at the level of the
instrument itself. "

And so forth. That is not necessarily so.


Why not?

Recently, Steven P. McNicoll posted:

"Neil Gould" wrote in message
. net...

On 4/2/07, you wrote:
"An altimeter indicates altitude at the level of the instrument
itself. "

and, again:
"In other words, an altimeter indicates altitude at the level of the
instrument itself. "

And so forth. That is not necessarily so.


Why not?

After puzzling the difficulties that several of us have had in trying to
explain the differences between "indicated" (e.g. what the pilot sees) --
and "senses" (how the altimeter is calibrated), I can only guess that for
you, sitting in the tower, there is no practical difference because you
are always at the same altitude. ;-) You can review some of the
excellent explanations that Jose and others have provided to answer your
question.

The original question asked whether the altimeter is set to indicate the
altitude at the wheels or "at the level...",
and if that question has been definitively answered, I missed it.

Neil

The original question asked whether the altimeter is set to indicate the
altitude at the wheels or "at the level...",
and if that question has been definitively answered, I missed it.

Somebody posted a link to the altimeter calibration procedure, and that
procedure calibrates the altimeter to the altitude of the instrument.
There is no provision in that document for adjusting the indicated
altitude to account for the relative position of the instrument in the
aircraft.

There may be another document that does so - an altimeter is not
certified for IFR just by itself, the =installation= has to be certified
too, and the FAA could easily require such an adjustment as not.

OTOH, there may =not= be another document which does so. When an
altimeter =installation= is certified, what procedure is followed?

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