The term ready-to-fly or RTF refers to a fully assembled radio controlled model aircraft which requires little or no final assembly to operate. RTF models generally are sold with necessary support gear in a single box. An engine-powered RTF requires the separate purchase of fuel; electrics are generally sold with everything except transmitter batteries. Inexpensive chargers are packed with models of this type as well. ParkZone and HobbyZone aircraft include eight heavy-duty AA batteries for the transmitter.