US Patent 7494320 Rotor for passively stable helicopter

A rotor (10) that enables an aircraft to become passively stable in hover. The inner part of the rotor blades (11) have a pitch angle fixed relative to a reference plane perpendicular to the rotor shaft (18) axis, and the tip of the rotor blades being connected to a ring (12) encircling the rotor. Each blade is connected to the rotor shaft by a separate hinge having a hinge axis perpendicular to both the rotor shaft axis and to the blade. Because the rotor blades can also easily twist the rotor can tilt freely in any direction. The rotor blades may be disconnected from the ring and folded up for easy transport.