Passive rotor pitch control system

A method for operating a vertical takeoff and landing (VTOL) vehicle comprising a rotor assembly that includes a passive rotor pitch control system, the method comprising:

• activating the rotor assembly to rotate to provide a pitch torque about a pitch axis associated with each of a plurality of rotors of the rotor assembly;
• converting a sum of the pitch torques about each of the pitch axes into an axial force on a pitch rod via a scotch yoke mechanism coupled to the pitch rod;
• increasing an angular velocity of rotation of the rotor assembly beyond a threshold angular velocity to increase the axial force greater than a spring force acting opposite the axial force on the pitch rod to rotate a pitch of each of the rotors from a first pitch state to a second pitch state via a pitch change assembly to provide lift of the VTOL vehicle for takeoff via the rotors;
• and
• decreasing the angular velocity of rotation of the rotor assembly less than the threshold angular velocity to decrease the axial force less than the spring force on the pitch rod to rotate the pitch of each of the rotors from the second pitch state to the first pitch state via the pitch change assembly to provide horizontal flight of the VTOL vehicle via the rotors.

A rotor assembly system comprising:

• a set of rotors that are configured to rotate at an angular velocity to provide thrust;
• and
• a passive rotor pitch control system, the passive rotor pitch control system comprising:
• a plurality of counterweights, each of the counterweights being associated with one of a respective plurality of rotors and being arranged to have a center of mass configured to provide a pitch torque about a pitch axis associated with the respective one of the rotors in response to rotation of the rotors about a rotation axis;
• a spring forcer comprising a pitch rod and a spring configured to provide a spring force on the pitch rod;
• and
• a pitch change assembly comprising a scotch yoke mechanism coupled to the counterweights and the pitch rod, wherein a sum of the pitch torques provided by the counterweights is provided on the scotch yoke mechanism to provide an axial force on the pitch rod opposite the spring force, the pitch change assembly being configured to rotate a pitch of each of the rotors from a first pitch state to a second pitch state in response to the angular velocity being greater than a threshold angular velocity at which the axial force becomes greater than the spring force.