RE: what "differential" control is...


On many models (and some full scale aircraft) the ailerons are setup to have more upward deflection movement than downward deflection. This gives a larger loss of lift on the side where the aileron moves up, than the increase on the opposite side.

The upward deflecting aileron can decrease drag on that side (usually noticed at low defelction angles, and with asymetrical airfoils) The downward deflection of an aileron not only adds lift, but increases drag. At low airspeed, the drag changes can be a larger factor than the lift increase, making the aircraft turn opposite to the desired direction.

An extreme of this is easy to demonstrate with a scale Cub model (or simlar) when taxiing near stall speed... such as right before lift-off or just after touch-down. The "barn door" ailerons can cause so much adverse yaw that the rudder can not compensate.

Adverse yaw effects with most models will be functionally inversely related to airspeed. In actuality...the aileron effect is still basicly (pitch angle has an effect...) the same, but higher speed makes the rudder/fin more effective, and thus you just don't se the yaw as much.