Q: Why it can't lock heading direction when I am in ALT mode and release all sticks?
A: use
SENSORS SETTINGS->CAL. JOYSTICK
to let the AP know the neutral points of your radio.
Q: Why the plane is not able to reach the target altitude in ALT/RTH/WPT/CIR modes?
A: First you need to make sure the plane can fly almost levelly in MAN mode. If it can't, please
use mechanical/electric trims to adjust it. Once you trim it on the radio please remember to
CAL.
JoySticks
Then test it in STB mode. If it sinks please increase the AOA (
Plane settings->PITCH TRIM
) a little
bit to increase the lift during level flight.
If the plane still not able to climb to the altitude we need in
ALT/RTH/WPT/CIR
modes, increase
PLANE SETTINGS->ALT_P
a little bit to allow the plane to maintain the altitude better.