ORIGINAL: Charlie P.

Full scale flight doesn't help with R/C much. When was the last time you flew a full-scale airplane while it was heading AT you?

If it's a nose-wheel trike have you ground-checked it so it rolls straight with the rudder centered? Common error is to have the nose wheel out of line with the rudder so they fight each other. The nose wheel has a lot more authority while in contact with the ground, but the instant you rotate if it is not set to the rudder the model suddenly turns when the rudder gets the airflow to be in command.

There is also a natural tendency to wander to port from the prop torque. Taildraggers, and in particular narrow carriaged biplanes need a bit of right rudder to compensate. Feed in throttle smoothly and gradually. Flooring it gives a lot of torque before the windspeed over the control surfaces gives you any control authority.