This may seem like a crazy idea, but what about attaching the pitot tube line to the NACA vent line and doing a test flight without the airspeed indicator.  There must be a way to convert the airspeed indication to PSI to determine how much pressure the NACA is generating.  In my ES the pitot line runs through the left wingtip.

 

I don't know how stupid it would be to fly with no airspeed indicator on purpose.  I know I wouldn't want to do it.  But that might be an easy way to get an idea of the NACA pressure.

 

Maybe there's someone out there with dual pitot tubes.

 

Mike Easley

Colorado Springs

Super ES