I have an FX79, and I have flown it both in STABILIZE and AUTO.
However, I must say I have a lot of issues with the center of gravity.
The frame comes with foam markers that supposedly indicate the CG. On the ground the plane is balanced but when flying it is EXTREMELY nose heavy. I have to pull up 75% of my stick just to keep it level.
AUTO mode probably does the same but you dont notice.
MANUAL mode is almost impossible to fly.
I crashed last week when trying to fix it, Im not sure exactly what happened.
I flew in STABILIZE and suddenly "Error Compass Variance" showed up. When I switched to AUTO , the plane just dove into the ground at full throttle.
Im not happy with the reaction of the pixhawk when these kind of errors happen, why would it crash because of a compass error? not cool.
Anyways, I hope someone has some comments regarding the CG, other than that I used the nominal settings and AUTOTUNE mode.
I flew today and experienced the same...
I found out that the CG is located on the wing screws that screw into the main fuselage and have wood underneath them.
The thing is, you have to, in manual mode without trims, center your elevators servos and pull them up 4mm, so that in the center position the tip of the elevators are 4mm up from the according wing level.
After that it should fly great!