"Peter" wrote in message
news

"Mike Rapoport" wrote:

Either way, the Shadin should be reading the same or lower than the OEM
OAT
guage.

I am sorry but I still don't get that. Total Air Temp should be SAT,
adjusted UPwards for the airflow heating. But different parts of the
aircraft will have different mach numbers. Which bit is TAT supposed
to represent?

Exactly, TAT represents SAT adjusted upwards for Mach. The problem with
your senario (160ktas, 10K', ISA and Shadin reads 3C higher) ) is that the
difference in readings is the same as the *total* calculated difference
between SAT and TAT. The OAT guage would need to have a local flow of
*zero* and the Shadin would need to have a local flow equal to the
freestream Mach number. Think about it this way:

Possibility #1 Both OEM OAT and Shadin displaying TAT and Shadin reads 3C
higher (stated condition)

Since total difference between SAT and TAT is 3C (calculated by Julian
earlier in thread) and the Shadin reads 3C higher, for the OEM guage to be
reading correctly the mach number at its location would have to be 0. To be
exact, the difference in Mach number has to be exactly the same as the speed
of the airplane, pretty unlikely.

Possibility #2 The OEM OAT is displaying TAT and the Shadin is displaying
SAT.

SAT is always lower than TAT so the Shadin should show a lower temp.

You could be right, which would presumably mean the stock OAT probe
has a higher mach number than anything else.

Two possibilities, either the airflow over the OEM OAT probe is zero or one
(or both) temperature readings are inaccurate, a much more likely senario.

Mike
MU-2