Yaw Controller explanation

I am trying to better understand the Yaw Controller of the Plane. Unfortunately, the documentation does not explain the Turn Coordination Calculation. In Git I found the following formula for it:

rate_offset = (GRAVITY_MSS / MAX(aspeed, float(aspd_min))) * sinf(bank_angle) * _K_FF;

I have been able to translate this so far:

Out = (g / MAX(Airspeed, float(aspd_min))) * sin(MeasuredBankAngle) * K_FF;

Unfortunately I can’t find an explanation for the remaining parameters. Could someone give me a link for the explanation or tell me what the remaining parameters stand for?

Would be grateful for any help

aspd_min is presumably the configured minimum airspeed set via ARSPD_FBW_MIN.

I think _K_FF comes from the YAW2SRV_RLL config parameter.

Thank you for the explanation. Can anyone confirm this with the K_FF wonder something because the parameter is nowhere mentioned a second time in the code

K_FF is mentioned in the AP_SteerController as well as the yaw controller. In the yaw controller I believe it’s defined at ardupilot/AP_YawController.cpp at Plane-4.2 · ArduPilot/ardupilot · GitHub

// @Param: 2SRV_RLL
// @DisplayName: Yaw coordination gain
// @Description: Gain to the yaw rate required to keep it consistent with the turn rate in a coordinated turn. Corrects for yaw tendencies after the turn is established. Increase yaw into the turn by raising. Increase yaw out of the turn by decreasing. Values outside of 0.9-1.1 range indicate airspeed calibration problems.
// @Range: 0.8 1.2
// @Increment: 0.05
// @User: Advanced
AP_GROUPINFO("2SRV_RLL",   3, AP_YawController, _K_FF,   1),

The comments in the code there exactly correspond to the YAW2SRV_RLL help text at Complete Parameter List — Plane documentation

Thank you for the Explanation