Aejar's thread is wonderful.

I like that he deals with the required number of channels too... however a distinction that he makes that is not overtly implied, is that 3 channel planes are acceptible trainers if they have aileron and elevator controls.

Some foam trainers ( cough * Parkzone Supercub * cough ) are three channel but only provide throttle, elevator, and rudder, instead of aileron.

You can learn to fly with a 3Ch plane equipped with throttle, elevator & aileron.

You only learn orientation with a plane equpped with throttle, elevator and rudder for the very reasons he states...