Indoors I am flying with the lowest possible rpm because of noise (and fear…)
Outdoors i choose much higher rpm-s because of wind gusts and more dynamics.
Unfortunately I have to adapt the control gains every time: at 1700rpm the RAT_P,I -s are around 50% higher than the outdoor values (2000rpm).
This seems to be logical as the aerodynamic forces on the blade foil are proportional to AoA*velocity^2. So the control sensitivity to a small swashplate movement (delta AoA on blade) will be 4 times higher at doubled rotor speed.
I have the same effect with one larger model airplane: either high gains but then oscillations at high flight speeds. Or lower gains, but then it is not stabilized at low speeds.
The solution is mostly a gain scheduling based on speed (or mach number in manned AC). For a model airplane maybe not so usable because of uncertanity of air speed estimation or measurement with pitot tube.
But for helicopter it could work well based on rotor rpm. Was this discussed already in ardupilot?