I'm having a strange bug where the helicopter keep turning to right as if the tail rotor is damaged. It's obviously not how helicppters suppossed to be work as it never happened in gunship 2000, battlefield 2, arma 3, and janes longbow.

it's not a joystick issue too because this still happens when I set pedal control to keyboard.

I can't properly control helicopter because of this. how to fix it ?

Sounds like a calibration issue with your controller.
See if you can bind the rudder to the proper axis or just unbind the rudder completely to see if the problem goes away.

I said that This also happens when I ser rudder control to keyboard.

By looking down I can see the pilot operating pedals when I pressed pedal inputs. This strange rotating happens even when he isn't pressing any pedals.

Now I found the solution, it was the cross couple option. by enabling it in dynamics option the strange rotation didn't happen anymore.