[secant0give]

With adverse Yaw, when you roll in one direction the plane yaws in the other. This is because the up going wing is producing more lift, obviously it needs too, to go up, but it's also producing more drag than the down going wing and the extra drag on the up going wing causes the model to yaw in that direction. differential can be used to over come this as Smuzz suggests, by having more aileron travel on the down going wing (more upward movement of the aileron) and less travel on the up going wing (Less downward movement of the aileron)

I hope this is not confusing, just remembering that for one side of a wing to go up, that side's aileron must go down and it's the down going aileron that causes the most drag.

It's more pronounced if the ailerons are mounted outboard on the wing, because they then have a greater moment arm. It's also more prounounced if the wing has a lot of diheadril. As Yaw couples with diheadril to create roll in the direction of Yaw and this will opose the disired direction of roll