Looking at the plane from the front the propeller is rotating counter clockwise. Picture smoke coming both ends of the propeller and imagine the plane moving forward. You would see a counter clockwise corkscrew shaped smoke trail that looks like a spring with coils with the plane being in the middle of the coiled spring. As the airstream moves around and back along the plane in a counter clockwise direction it is similar in shape to the the spring analogy. The airstream ultimately strikes the port side of the vertical stabilzer, pushing on it (F=MA) and causing the plane to yaw to port (left). This would be true regardless of the attitude of the plane. If you can envision the airstream to be the coiled spring then the faster the plane goes the more stretched the spring becomes and less of it strikes the vertical stab. If the plane slows down or the power increases then the spring coils become tighter and more of it strikes that vertical stab causing a bigger yaw to the left.

Howard