A drilling system may include a plurality of robotic drilling units. Each one of the robotic drilling units may include a drill end effector positioned inside a barrel section. The barrel section may be configured as a composite sandwich structure having an inner face sheet. The robotic drilling units maybe operable in synchronized movement with one another to drill a plurality of perforations into the inner face sheet using the drill end effectors in a manner providing a predetermined percent-open-area of the inner face sheet.