Autotune (or Auto Tune) that is present in INAV for quite a long time is a working solution for tuning PID (or rather PIFF) controller used by INAV on fixed wings (all airplanes, flying wings). Not like all the attempts designed for multirotors, this one actually works.

INAV Autotune can be used on any airplane and is fairly simple to use as long as you follow a few simple steps: