Slowrotor,
An absolutely rigid rotor is just not achievable, since we are dealing with large inertias at relatively high RPM. Comanche achieved 15% effective hinge offset, and has about the most rigid rotor practical. This reduces the azimuth lead angle from 90' to about 75', but we are still dealing with an aerogyroscopic system.
The flexbeams mentioned in the patent with be the tension torsion packs that IFMU discusses. These are basically a pack of steel laminate "feeler guages", which transfer bending loads and tension but allow torsional freedom. The result is a high effective hinge offset. The only potential downside is that they can suffer reduced fatigue life from lead-lag forces, since guages can buckle with in plane bending.
Aerokopter Sanka example mentioned under title "Rotor System"
Mart