(under subclass 24) Propelled aeronautical machines sustained by their buoyancy relative to the air, having also provision for sustentation or vertical lift by means of screw propellers arranged to develop a substantial component of thrust in a vertical direction.
(1) Note. For helicopters having also sustaining wings, see this class, subclass 6.
(2) Note. For helicopters without airplane wings, see this class, subclasses 17.11+.
