The simplest possible explanation:
Correct, the effect causing this is called torque.
Before anything else - I would advise that you try flying planes with two engines and counter rotating propellers, much like a P-38.
With trim you can counter this but only at certain speeds. The faster you go the more airflow runs over your wings and pulling you stronger in one direction.
In IL2, much like it was in WW2, some planes don't have an option - can not be trimmed. And some planes are automatically trimmed for certain speeds. When applying trim in most cases you need to use a lot of it, especially since you're using keyboard for the job.
As for the take off - never apply full throttle. Use no more than 50-60% until you reach significant speed before you apply full power. Even then with some planes you will need to turn rudder fully in one direction. I do hope that you have at least a joystick with 4 axes (X, Y, Z for rudder and one for throttle). If not, you can disable 'engine throttle' under settings to suit your flying needs.
