It's true that most R/C planes turn just fine with ailerons only.

However, it's worth mentioning that a few planes turn better when you use both ailerons and rudder. A good example is the J3 Cub, both full-size and models. With ailerons alone, turns are sloppy and slow. Using both aileron and rudder results in a nice, smooth turn, called a coordinated turn.

My 47" Cub definitely needs its rudder for good turns. So does the giant scale 12-foot Cub belonging to one of our club members. And so does the full-size Cub.

Search for the term "coordinated turn" for an explanation.

- Jeff