700 Class gas engine helicopter tail wave

ArduCopter Traditional Helicopter
1

Hi,
I use a 700 class gasline heli in poshold mode but the tail is always wave, you could see in log

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and I used governor to keep the rotor speed but have some shake
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I’m not sure it may cause the tail wave
It is very appreciate if anyone could give some suggest
the log attached
https://drive.google.com/file/d/1Vfc4XQcy-ZKxhtjIaOK-8DjZEVi4nHfT/view?usp=sharing

2

I find the root cause is the low headspeed, the gas engine is always much lower headspeed than other piston engine
in wiki page Preparing for Tuning — Copter documentation (ardupilot.org) suggest increase the ATC_RAT_YAW_FF to 0.5, but I think that is not too much benefit in performence
I just change the tail rotor to 120mm(105 before)
someone maybe suggest to increase the headspeed to get better performance, but that may cause higher temperature of engine, so in my opinion, change the diameter of tail rotor as large as you can, special for the gas engine