units of measurement on altimeters

On Sun, 7 Mar 2004 17:42:25 -0000, "Julian Scarfe"
wrote:

"Jukka K. Korpela" wrote in message
...

In practice, using hPa means being just _nominally_ metric, i.e. using
actually millibars but under a different name. The odd thing is that
the correct kPa would be more practical.

How can you possibly suggest that it would be more "practical" to use kPa?
There is an installed base of tens of thousands of altimeters in aircraft
out there that are calibrated in mbar. Describing them as hPa makes it
clear what the unit is for someone familiar with the SI, without risking
accidents through unit confusion.

The preference to use powers of 1000 is just a preference because
practicality and pragmatism is sometimes more important than an arbitrary
recommendation. This is a perfect example of where pragmatism should (and
does) win.

Oh, good grief.

Does anybody use feet for altitude?

Do all of the analog instruments show all the digits in those feet?


Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

"Gene Nygaard" wrote in message
...
On Sun, 7 Mar 2004 17:42:25 -0000, "Julian Scarfe"
wrote:

"Jukka K. Korpela" wrote in message
...

In practice, using hPa means being just _nominally_ metric, i.e. using
actually millibars but under a different name. The odd thing is that
the correct kPa would be more practical.

How can you possibly suggest that it would be more "practical" to use
kPa?
There is an installed base of tens of thousands of altimeters in aircraft
out there that are calibrated in mbar. Describing them as hPa makes it
clear what the unit is for someone familiar with the SI, without risking
accidents through unit confusion.

The preference to use powers of 1000 is just a preference because
practicality and pragmatism is sometimes more important than an arbitrary
recommendation. This is a perfect example of where pragmatism should
(and
does) win.

Oh, good grief.

Does anybody use feet for altitude?

Do all of the analog instruments show all the digits in those feet?


An just to add to the confusion our aircraft uses pieze for manifold
pressure

Does anybody use feet for altitude?

Everyone except the Former USSR and China, as near as I can figure.

all the best -- Dan Ford
email: (requires authentication)

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

On Sun, 07 Mar 2004 17:33:47 -0500, Cub Driver
wrote:


Does anybody use feet for altitude?

Everyone except the Former USSR and China, as near as I can figure.

bravo--you were able to answer the rhetorical question part.

What about the rest of it?

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

"Gene Nygaard" wrote in message
...

The preference to use powers of 1000 is just a preference because
practicality and pragmatism is sometimes more important than an arbitrary
recommendation. This is a perfect example of where pragmatism should
(and
does) win.

Oh, good grief.

Does anybody use feet for altitude?

Do all of the analog instruments show all the digits in those feet?

Pilots have become accustomed to using feet for altitude. Can you imagine
the confusion that would arise if the unit suddenly shifted by a factor of
10?

"Descend and maintain 300 decafeet"

Any room for confusion there?

We already have trouble enough with pilots screwing up inHg to mbar
conversions. What does an altimeter setting of "nine ninety two" mean?

As a physicist and a pilot, I'd rather live with the inconvenience of using
a hecto prefix for stuff that comes across my desk than risking confusion in
the cockpit. So would ICAO.

Julian Scarfe

"Julian Scarfe" wrote:

We already have trouble enough with pilots screwing up inHg to mbar
conversions.

So while you take the trouble, wouldn't it be best to move to something
that lasts, due to being part of a system that is meant to be applied
in all areas of life when expressing physical quantities? It's better
to move directly to the SI system as recommended in general, rather
than first moving, say, to a partly decimal-based variant of the Anglo-
Saxon system, or - to take an example about different quantities -
first move from the use of different gallons to a Unified Gallon, then
to hectoliters, later to what the SI system really recommends.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

"Julian Scarfe" wrote:

We already have trouble enough with pilots screwing up inHg to mbar
conversions.

"Jukka K. Korpela" wrote in message
. ..

So while you take the trouble, wouldn't it be best to move to something
that lasts, due to being part of a system that is meant to be applied
in all areas of life when expressing physical quantities? It's better
to move directly to the SI system as recommended in general, rather
than first moving, say, to a partly decimal-based variant of the Anglo-
Saxon system, or - to take an example about different quantities -
first move from the use of different gallons to a Unified Gallon, then
to hectoliters, later to what the SI system really recommends.

The SI is equally happy with hPa or kPa. You've pulled out a standard from
ISO, I think, that is designed to help you make a choice when there is no
reason to do differently. I agree that, if there were no other factors
influencing choice of unit, multiples of 1000 are a good default. But
you've picked on a case where there *are* clearly good reasons -- the size
of the unit, and the equivalence to mbar -- that make hPa a very sensible
and pragmatic choice.

Julian

On Mon, 8 Mar 2004 at 20:08:38 in message
, Julian Scarfe
wrote:

The SI is equally happy with hPa or kPa. You've pulled out a standard from
ISO, I think, that is designed to help you make a choice when there is no
reason to do differently. I agree that, if there were no other factors
influencing choice of unit, multiples of 1000 are a good default. But
you've picked on a case where there *are* clearly good reasons -- the size
of the unit, and the equivalence to mbar -- that make hPa a very sensible
and pragmatic choice.

I know little about this but isn't there a case for making the format of
digits used specific to the function as far as possible?

Call 101 decimal 5; altimeter 1015; Heading 101; altitude 1 thousand 1
hundred for example?

Just a thought.
--
David CL Francis

David CL Francis wrote:

Call 101 decimal 5; altimeter 1015; Heading 101; altitude 1 thousand 1
hundred for example?

Which means you're right back to hPa, as far as the altimeter goes.

George Patterson
Battle, n; A method of untying with the teeth a political knot that would
not yield to the tongue.

In misc.metric-system Julian Scarfe wrote:
Pilots have become accustomed to using feet for altitude. Can you imagine

As a european pilot I would prefer meters.
But how to rearrange separation standards, any ideas?

--
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--Pfaffenwaldring 27 Raum 114, D-70569 Stuttgart Uni Computeranwendungen
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