"Gord Beaman" wrote in message
...
"Jim Knoyle" wrote:




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

Hang on here a second now Jim, you still need two samples. As Dan
says you need 'static pressure' to read the altitude from and you
need 'pitot pressure' (ram air pressure) as well as the static
pressure to derive the airspeed reading from. Sounds like you're
saying that you can read 'both' from just the 'ram air pressure'
alone. Or did I misunderstand you?

Darn, Gord, I thought it sounded clear to me... still do.
It must be getting late. The book (and I) says that the
Ps component of Total Pressure must be taken into account.
The Ps from the other DADC fitting (labeled static) is used
to accomplish this. That's what I meant by "it does factor in..."
Can't tell (the value of) one without the other.

I'm sure that you know that lots of pitot tubes have both a
static port (flush mount on the side) and a 'ram air port' the
hole in the front to collect 'pitot pressure'.

The combined pitot/static probe which I referred to by
"The Ps, whether obtained from the static port(s) on the probe
or flush mounted ports on the fuselage."

We all agree, we just don't know it. Sorry if I confused
the issue.

JK