Does any one have any ideas on the best location for
the OAT probe?

In my Legacy it is installed inside the NACA duct on
the pilot side of the plane.  The problem is that
while on the ground it reads exactly the same as the
oil temp probe and exactly the same as the thermometer
on the wall of the hanger.  However, in flight it
always reads much higher than actual outside
temperature.

For example, yesterday I took the temp reported on
ASOS which was 20C, I converted that to 68F.  I
subtracted the lapse rate of 3C or 5.4F degrees for
each thousand feet in the air where it should have
been 14F degrees.  If I used 2C as the lapse rate it
would have been 34F degrees.  On my Chelton it read
71F at 10,500'.  This happens on every flight so it is
not a temp inversion.  There must be something wrong
with the location.  I cannot believe it is getting
alot of heat from the engine with all the cold air
blasting across the probe through this fresh air vent
which is always open.  What else could it be?????  Any
ideas?  Is there a better location for the probe?

Art,

 

One must be careful that interior heat does not reach the temp probe - this includes heating the wire near the probe and the mounting surface.  On my 320, using the button housing supplied by Rocky Mountain Instruments, I have mounted the probe on the wing bottom just forward of the middle landing gear door opening.  Thus, the probe is protected from the sun when flying with the bottom towards earth and the wires travel thru the wheel well that pretty much stays at the outside air temp.

 

Has the probe been tested by placing it in ice water that should yield a temperature close to 0C (32F)?