I release a new firmware for Turnigy 9x,
You can use telemetry from APM (watching battery voltage and GPS informations).
You can tune major value of PID (not all).
And the last you can change flight mod via Mavlink or PPM chanel.
Actually I tested only on the last version of AduCopter, I thing you can easily change the sources code to adapt for ArduPlane
Project home :
Download binary :
Main screen with alternate voltage display (transmitter and APM)
On the picture, '20.1' is the voltage of APM and 'STAB' is the flight mod
Mavlink infos screen
Mavlink GPS screen
PID settings screen (can modify P & I parameters)
Settings flight mod cmd
I had two another parameters :