RE: cub ground roll
Something that might help you understand why the need for rudder, and why the amount needed changes during the ground roll, is understanding P-Factor. The nose high stance of the A/C contributes to the problem. At the initial throttle up the propeller is pulling straight forward on an aircraft with no right thrust. As the A/C starts to move the relative wind hits the propeller at an angle, causing the downward turning blade to have a greater pitch in relation to the relative wind. This causes the right side (on props that turn clockwise from the cockpit) to pull harder then the left. As speed increases the pull gets stronger until you are able to raise the nose and reduce the angle that the relative wind is hitting the prop, therefore when the tail comes up you will need far less rudder. This is the point that most people over control. Rt thrust will alleviate some of the left turning problems, but still will not eliminate them. excessive rt thrust will just make it worse causing it to shift from pulling rt then left and back to rtPractice is key, but understanding the basics of why it is happening will make it a shorter learning curve.