"B2431" wrote in message
...
From: "Jim Knoyle"
Date: 1/17/2004 8:00 PM Central Standard Time
Message-id:


"B2431" wrote in message
...
From: "Jim Knoyle"
Date: 1/17/2004 3:48 PM Central Standard Time
Message-id:


[ snip ]

The hole on the front only detects pitot pressure. If there are holes
on
the
side are for detecting static pressure.


No, sorry Dan, you'll have to refer to a more modern air data computer.
When the label at the top of the ADC switched from pitot to total, the
definition for Total Pressure (Pt) was given as:
"This is a pressure input (from the aircraft pitot probe) which varies
both with altitude and aircraft speed. (Range 3.11 to 42.50 in. Hg.)"
*This was a direct quote from a Honeywell HG280D DADC guide*
The book goes on to explain how the delta Ps is removed to arrive at
a more accurate airspeed. The Ps, whether obtained from the static
port(s) on the probe or flush mounted ports on the fuselage, is fed
through another fitting on the DADC (labeled static) and is something
else entirely. It does factor in to the math.

JK

OK, I see where you are coming from. The pitot pressure DOES vary by
altitude.
To compensate for that when measuring airspeed you use static pressure to
give
you altitude. Some aircraft detect static pressure from holes on the side
of
the pitot tube and others have the static ports located elswhere.

In another recent part of this thread that didn't get cross-posted from
a.d.a.
(is that cheering I hear? ) I mention how the 727, 757 & DC10 use the
flush mounted static ports whereas the 737, 747 & 767 use the combined
pitot/static probe. Since Tarver seems to infer that the combined
pitot/static
probe is somehow better, I couldn't resist getting in a jab as to how the
777
uses the seperate pitot tubes on the nose and the flush mounted static ports
on the fuselage. Seems the Boeing Engineers ignore his mud bee warnings.
They do use analog/digital conversion right at the probe or port and run
wiring instead of plumbing. Sounds like a good idea to me.

I would be interested in seeing a schematic of your aircraft's
pitot-static
systems including DADC. I have never worked on DADC. I did work on the
CADC
abomination on the F-4E.

In this long running sparring with Tarver, I've placed a couple diagrams on
"his" page: http://home.att.net/~j.knoyle/the_ta...hronicles.html
The DC10 plumbing diagram at the bottom of this came from the DADC book
mentioned above: http://home.att.net/~j.knoyle/mechtest.html
There is a 767 plumbing diagram at the bottom of this page:
http://home.att.net/~j.knoyle/pitot.html
Somewhere I came across this great 777 presentation:
http://euler.ecs.umass.edu/ece655/Boeing777.ppt

JK