Lead/Lag hinges are needed to compensate for geometric imbalances (coriolis effect) while flapping. because the R22 is rigid in plane it maintains even centre of mass on both blades, therefore neither blade wants to accelerate relative to the other, hense no need for lead lag hinges. Tri-hinge design is to undersling the load which gives head ability to teeter.
That's ballpark my level of knowledge explaination. apologies for any inaccuracies in terminology
NB