John -

 

The Jim Frantz AoA system (now sold by, I think, Advanced Flight Systems) uses pitot and static information, so you would get erroneous AoA readings with a plugged pitot tube.

 

Specifically, the system depends on the relationship between the differential pressure across the wing from top to bottom (lets call that DeltaP) and the dynamic pressure which we recall is the difference between pitot and static pressure (lets call that Q).  It turns out that the quotient DeltaP/Q is proportional to angle of attack if you pick the right point along the chord (which is why the instructions tell you to put the pressure ports in certain places).  Therefore, if your pitot tube is plugged, DeltaP/Q will be off and so will the alpha readout.

 

Now, if you're using a different system such as a Dynon, all bets are off.  I don't know how that is mechanized.

 

- Rob Wolf