da Rock

With our models, an awful lot of our "design" is actually development, and done after the airplane is flying. Aileron differential is one of those things that is most often discovered to be needed, not cleverly designed into our models ahead of time.

Why does it happen. Bottom line is that the wing going up also goes back, and the wing going down goes forward. Why? Because one side loses drag while the other side's drag increases.

It usually happens with cambered airfoils. It happens because the aileron going up actually creates a profile that has less drag than before, and the aileron going down simply increases the drag that side was already producing.

Creating lift creates drag. The wing with the up going aileron is creating less lift than before so creates less drag than before. The down going aileron is creating a profile with more lift than before and creates more drag than before.

We discover that our latest model yaws the wrong way when we try to turn with aileron/elevator and we wind up learning about adverse aileron-induced yaw. And we decide to fix it. What's the most obvious way? Change what's causing the problem, the aileron movement.