A couple books written by full size aerobatic pilots state that a spin is a Rudder-Elevator manuever. Most planes should not need ailerons to do it. In fact, they say that with some planes, the ailerons are ineffective, because by the time the plane actually properly enters the spin, the wing is stalled to the point the ailerons don't have an effect. Of course, that is probably because a correct spin is entered from a full stall.