The FAA operating limitation for EA-B requires a category and class for the pilot in command. So for a RV-9 would need a Private Pilot with Airplane rating. For Sport Pilot you would need a Sport Pilot certificate with a logbook endorsement for Category, class and make and model. 5 hours solo flight required (61.313). I don't understand the reason for this solo limitation. It is contrary to the FAR that allows solo flight without a rating in Experimental aircraft.