Extra Kollsman Altimeter Poimters

In article ,
says...

In this case I should have said -700 which is how much the pressure is
higher than sea level standard.

Hmm..... That's almost 200 feet off of what the difference actually is,
wich is something just shy of -900 or so, from memory, between 2992 and
3090. If that's it, the altimeter's scale factors are way off. Though
your explaination makes sense if they go negative above 2992 and
positive below 2992.

When set to zero the window reads 29.92 and the altimeter reads pressure
altitude. Conversely, when they are set to pressure altitude, the
altimeter reads zero.

How about a request. A series of images. Pick a day, tell us the
altitude of the desk that the altimeter is sitting on, set it to the
local altimeter setting and take a series of pictures of that setting,
plus a few tenths above and below.

Then another series at 2992, plus a few tenths above and below if they
don't overlap too badly with the first series.

And if you're really a glutton for punishment and have free time to
waste, a series at 2992, but in an airplane at several altitudes.

Then somebody is bound to figure out what they really do.

--Carlos V.

The little black triangle look like an altitude bug. It looks like it
can be moved around to whatever position you choose. But then I haven't
read the whole thread to know if that's true.



You guys are missing the little black triangle just to the left of the 1000' label...does it move?

Icebound wrote:
"Lakeview Bill" wrote in message
m...
Here's a modern Falcon Gauge unit with the same markings...

http://www.falcongauge.com/images/pr...sitiveALT1.jpg



Where are they? I cannot spot any markers in your pic other than the 3
indicated-altitude pointers.

The moving indicators that dennise9 is writing about, are the tiny triangles
at the 3, and just to the right of the nine.... reading minus-700 in the
pic, as per the article which I posted about earlier. Since (s)he has
moved them independently of the Kollsman Knob (partly in response to my
speculation, I must confess), they are probably slightly in error for the
altimeter setting shown ( 30.90 )... I would expect closer to -1000 (or the
outer pointers at 0 and the inner on the 9)

So I am recommending putting the Kollsman at 29.92, resetting the markers
independently to zero zero, and then we would see if they go to near -1000
(as I would expect), when the Kollsman is put back to 30.92.

Or, if (s)he has already reset the pointers to zero-zero at 29.92, then -700
might just be a more accurate reflection of the 1.00 inch change in
altimeter setting between 29.92 and 30.92, than is the usual rule-of-thumb:
100 feet per .1 inch in altimeter setting.


Wow, what a group! I never expected such discission on my old
altimeter. Thanks! From the posts, it makes me think that I have a real
antique here with three hands and two "reference markers". After
reading all your posts, together with Iceman's excellent link and
comments, my conclusion is this.

The reference markers are simply the "altitude equivalent" of the
pressure in the Kollsman window, referenced to zero-zero at 29.92. The
markers show positive altitudes (CW = positive) for Kollsman settings
lower than 29.92 and negative (CCW = negative) altidudes for Kollsman
settings above 29.92.

With the reference markers set to zero-zero at 29.92,at my present
location (about 5,300 ft above sea level), a manual 1 inch Kollsman
change to 28.92 gives a reference marker indication of about +940 feet.
A manual 1 inch Kollsman change to 30.92 shows a reference marker
indication of about minus 920 feet. I can't explain why a 1 inch change
above and below 29.92 doesn't give the same absolute altitude change
e.g. +920 ft, and -920 ft. Instead I get +940 ft. and -920 ft.

In todays times, as someone has mentioned, the only use I can see for
the markers is as follows. For situations when the Kollsman wndow is
'blanked out' one could take the local given pressure, convert that
into an equivalent altitude, dial it in with the reference markers,
then read the correct altitude above MSL from the normal hands.

Dennis

wrote in message
oups.com...

Wow, what a group! I never expected such discission on my old
altimeter. Thanks! From the posts, it makes me think that I have a real
antique here with three hands and two "reference markers". After
reading all your posts, together with Iceman's excellent link and
comments, my conclusion is this.

The reference markers are simply the "altitude equivalent" of the
pressure in the Kollsman window, referenced to zero-zero at 29.92. The
markers show positive altitudes (CW = positive) for Kollsman settings
lower than 29.92 and negative (CCW = negative) altidudes for Kollsman
settings above 29.92.

With the reference markers set to zero-zero at 29.92,at my present
location (about 5,300 ft above sea level), a manual 1 inch Kollsman
change to 28.92 gives a reference marker indication of about +940 feet.
A manual 1 inch Kollsman change to 30.92 shows a reference marker
indication of about minus 920 feet. I can't explain why a 1 inch change
above and below 29.92 doesn't give the same absolute altitude change
e.g. +920 ft, and -920 ft. Instead I get +940 ft. and -920 ft.


It *is* explainable and consistent.

The difference between 29.92 and 30.92 is within a *higher* average pressure
range, and hence denser air, and hence a change from one pressure level to
another is actually a *smaller* altitude change. Between 29.92 and 28.82,
it is a *lower* average pressure, less dense air, and so you have to go
farther in order to get the same 1.00 pressure change.... apparently about
20 feet farther, according to your instrument.

In article .com,
wrote:

In todays times, as someone has mentioned, the only use I can see for
the markers is as follows. For situations when the Kollsman wndow is
'blanked out' one could take the local given pressure, convert that
into an equivalent altitude, dial it in with the reference markers,
then read the correct altitude above MSL from the normal hands.

The use was to set field pressure Altitude on the reference markers so
that your altimeter reads QFE... that is altitude above Field Elevation.

Simplifies flying the pattern at 800ft, 1500, or what ever is normal for
your airport, but the real use is for approach where your minimums are
200 ft... instead of looking for a DH of 5,500, you would be looking for
200.

American and Eastern used them this way for decades. In older aircraft,
one altimeter was set to QNH and the other to QFE for approach. Later, a
third altimeter was installed and both pilots would look at QFE on
approach.

When you only fly to one or two airports in a day, it's not that big a
deal, but when you are making 6 to 8 landings with low ceilings,
descending to the 200, 300, 400, or whatever is on the plate simplifies
things a lot.

Over the long haul, it's nicer to find concrete than foliage.