From: "John R Weiss"
Date: 1/19/2004 2:05 PM Central Standard Time
Message-id: _LWOb.85390$sv6.201965@attbi_s52

"Mary Shafer" wrote...

Did you also say that you can't correct them without OAT, outside air
temperature? That's the third element of a pitot-static air data
system.

What is required -- static air temperature (SAT) or total air temperature
(TAT)
for the OAT correction?

If TAT, how is it measured, and how many thermocouples are required, in what
configuration?


It's OAT. Air speed measured with just pitot and static pressure is referred to
as indicated airspeed, IAS. If you temperature compensate it becomes true air
speed, TAS.

Basic mechanical analog TAS indicators use one of two methods of temperature
compensation: one uses a capillary tube from a bulb mounted on the exterior of
the of the aircraft , the other uses a knob where you can manually dial in OAT.
The C-130s I worked on had the capillary type.

Thermocouples are not used for electrically detected OAT. What is used is a
temperature bulb usually mounted flush to the skin of the aircraft. If you look
at a C-130 you will see a 2"(?) disk on the skin on either side ofthe nose
wheel well. Those are temperature bulbs. They vary in resistance due to
temperature change.

For the life of me I can't remember if the resistance increases or decreases
with temperature drop.

Dan, U.S. Air Force, retired