Originally Posted by
riff_raff
"Bearingless" rotors still have some arrangement that permits adjustment of the blade pitch. Usually a torsionally flexible attachment structure or a laminated elastomeric bearing. However, they do not provide adequate stiffness for rigid rotor systems. Look at the Sikorsky rigid rotor hub designs that use rolling element blade feather bearings.
Riff, while requiring a different flexbeam arrangement than a conventional flexbeam rotor like AH-1Y/Z, RAH-66, or EC-135, a stiff out of plane rotor can have a flexbeam. The Sikorsky X-Wing used a flexbeam with a torisionally soft I cross section but was stiff in the flap and lag directions.
Sikorsky Archives | X-Wing
If you browse around on Google patents, it's clear Sikorsky continues to examine atypical applications of flexbeam type rotors, including for coaxial aircraft. In fact, if you examine good photos of the S-97, the inboard half of the blade looks proportionally thicker than the X-2 does, and early ground run photos with the hub fairings off show the blade composite wrapping around the outside of the hub structure. They haven't said as much (to my recollection), but Raider might well be a 'rigid' flexbeam rotor, at least flexible in the torsion direction.