On Sep 13, 9:01 am, The Visitor wrote:
No, not trolling.

My friend is convinced that the altimeter setting, which is corrected to
sea level (?) would be incorrect to use. Also incorrect would be the Sea
Level Pressure listed at the end of a Metar as it is also corrected to
sea level. (Surface analysis maps also.) He needs the absolute station
pressure not corrected to anything. I told him to use that but he feels
he should be taking off three odd inches to come up with the actual
pressure. I told him that lapse rate is an average used in an air mass,
not at the bottom of an air mass along the ground. valid say if he
climbed a 1000 foot tower. But I say anytime you have a station pressure
of 26 to 27 inches you will be in a real hurricane. He says, sure, but
that is at sea level. And sure we all know at different elevations, the
air is thinner. Pilots are not equipped to get through this I guess as
he has found atpl pilots (me too) give him different answers.

I am now thinking he is right, but wrong to use the one inch per
thousand feet assumption as the atmosphere is rarely standard and it is
really just for altimeter callibrations. Yet this has some strange
implications for the barometer on my wall.

He has a ton of measuring equipment and I don't know why he doesn't just
get a guage for this to.

I was hoping for a met-whiz who actually knew what is done to the raw
data ("corrected to sea level")

Any how thanks for trying.

John

Denny wrote:
On Sep 12, 6:20 pm, The Visitor wrote:

Opps, meant to put this in the piloting group. Oh well, same crowd. Sorry.

The Visitor wrote:

So I have a friend going out to Red Deer Alberta to so some industial
air flow measurements of a sort. In his calculations he must enter the
atmospheric pressure. I thought, no problem, just get it from the metar
for Red Deer.

Red Deer is 3000 odd feet asl. If they are reporting 29.92 is the actual
pressure some three inches lower? But that is corrected for temperature.
Perhaps just use the pressure at the end, I think it is in Hectopascals
but is also corrected to Sea Level. What is the actual station pressure
he should use?

John- Hide quoted text -

- Show quoted text -

The volume of replies is stunning... I suspect the gang smells a
troll...
However I am full of the milk of human kindness this AM... So,here is
the answer:

Kindly purchase any version of the private pilots exam preparation
book or CD, such as that from the Kings, et. al. and all your
questions will be answered...

denny

You will have to work with the pressures given in a standard
atmosphere table that you can get from any engineering text. The
altimeter setting only gives the deviation from the standard
pressure. It assumes 29.92 inches at the standard pressure.
Deviations are proportional (I think).