I'm gonna chime in here again. I have flown quite a few of these with various students and I now have finally come across one that has shown the tendencies listed in this thread.

Here is what we found. The engine had too much right thrust. The wing extensions were not placed on each wing half equally. One side was closer to the fuselage than the other. This showed it's ugly head right after takeoff, the plane rolled hard right and full elft aileron and rudder would only level it, I chopped power and instantly had good control.

On this plane we corrected each problem individually and all is now well and good. The AFS was never functional/installed on any of them and as the student progressed we removed the "extra goodies".

So if there are problems, simple checks are usually all that is needed. It's a good trainer and can take a pretty good beating. I saw one cartwheel pretty hard and all it did was pop the gear out and crush the nose. We trimmed a 1/4 inch off the end of the gear and snapped it back into place and CA'd the nose and we were back in the air in short order.

Yes there are better trainers out there, like the LT-40 and others but for the price, the Nexstar is not bad.