Al,
Ok, Part of my misunderstanding lies in the fact that my
field elevation is 55 feet. So both will read close to the same
here. You are saying that his readings would have to be corrected for his
5000 foot altitude which is about 1 inch per 1K feet?
Bill
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Al Gietzen
Sent: Tuesday, June 23, 2009 2:12
PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: progress
report #347c
Al,
Hmmmm,
Further explanation would be helpful here. I thought that the
altimeter
was actually reading the air column weight or pressure at its
location.
If you set the altimeter to the field elevation, it seems it
should
read the barometric pressure in the window
Gees; I was hoping you
wouldn’t ask – then I wouldn’t have to think about itJ.
Well; it goes something
like this; your altimeter setting is the barometric pressure of the station as
if the station were at sea level. So the altimeter setting is barometric
pressure with an altitude correction applied. Your MAP is absolute
ambient pressure.
Absolute pressure is measurement relative to a perfect vacuum, as in outer
space. A zero reading occurs when the pressure is reduced to near perfect
vacuum conditions. The ambient atmospheric pressure at sea level is
approximately 29.92 inches of mercury, or 14.7 pounds per square inch, or 760
mm of mercury. As you go up the ambient atmospheric pressure decreases and your
Absolute pressure gauge (MAP) reading also decreases.
I have a chart of the
barometric vs ambient pressure, but I don’t know where I got it. Anybody
know? I’ll check the internet and see if I can find something; or I
could scan it and send it.
Al G