Plane's tail fin moves on its own with SAS turned ON

[The Aziz]

As in the title. Aside from obvious sliding even with full brakes, my new plane, and few others, does this:

No matter where I place it, no matter whan kind, it always go left or right with SAS ON. When I turn it off it goes back to normal state. The part is perfectly centered. 1.12 with both expansions. With that the plane is very hard to control and can't really fly straight. I can turn off the Yaw or set authority limit to 0 but then it's useless.

[Dr. Kerbal]

It could be SAS trying to stablize the craft when it already stablized. 

Edited July 14, 2021 by Dr. Kerbal

[HvP]

It's just trying to keep your plane pointed in the forward direction.

But, because there is little to no forward movement the tail fin doesn't have any wind passing around it to affect the plane's orientation, so the SAS tries turning even more.

My recommendation is to simply leave SAS off until you are moving fast enough to begin lifting off the runway. By then there is enough atmospheric control for the SAS to get proper feedback.

[jimmymcgoochie]

You’re not moving, but due to the way the runway is laid out there are often minor forces that can cause a stationary plane to rotate slightly. SAS tries to counter that with yaw input, which includes the rudder even though it isn’t moving so has no effect. Start your takeoff roll with the SAS off and then enable it once you’re moving and it should be OK, and check that your nose gear have their friction setting turned down as that can cause runway instability.