(under subclass 4) Aeronautical machines having provision for sustentation in part or entirely by aerodynamic action on airfoils in fixed relation to the machines, 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 without airplane wings, see this class, subclasses 17.11+.
(2) Note. For lighter-than-air craft partially sustained by helicopter propellers, see this class, subclass 26.
