Is it just for me or do airplanes not go straight down the runway?

Sometimes there's a very small part that is not placed in a symetric position relative to the COM and central chip, and also, wheels are kinda unstable naturally.

@sflanker its not actually any of the below mentioned stuff, its just that the wheels are kinda unstable, to fix it just increase forward/sideways friction on the back wheels, atleast thats what worked for me.

I haven't made a lot of planes by my SSTO does sometimes yaw a little bit, but that's what vertical control surfaces are for (i.e. rudders). I'm not sure what causes this, I don't think SR2 simulates wind, so could be something to do with torque of spinning engines (if you're using jets) and gyros. Or I suppose it could theoretically be some sort of Coriolis effect due to the rotation of the planet. And I'm obviously assuming your plane is perfectly symmetrical.