Jack
To amplify fobotcso's post
As you probably realise the advantages of the cylindrical or conical probe as the sensor for the Airstream Direction Detection instrument is that it is reasonably robust compared to the sort of flightest wind vane one sees out on booms ahead of test aircraft. It is also easy to heat and keep from icing up.
It works because the pressure sensed by the two rows of slots (of whichever shape of probe) is fed to the opposite sides of a paddle type vane inside a cylinder that is free to rotate up to perhaps 50 deg and also connected to the probe. Thus as you surmised the probe settles at an angle giving equal pressure either side of the paddle and this angle varies with the direction of the airflow approaching the probe. If you like the probe aligns itself so that the stagnation point of the approaching air is between the two rows of slots.
My kingdom for a picture!
NB If your library has AP3456 you will find a nice picture of the ADD system workings in Vol 3 Part 2 Section 3 Ch 4 Page 2 (AL6)
My recommendation is that you use a wind vane on your model.
Regards
John