Lu,
thanks for taking time to read the article.
I think it is correct that R/C helos usually have some form of fly-bar. 2-bladed teetering rotorheads are common. But the article says clearly that the fly-bar actually tends to reduce the need for swashplate offset.
It is not the cause of the offset.
The real cause is that the blades will flap into position more quickly when there is coupling between pitch and flap.
This is the case in the full size R-22
When the R-22 blades flap, pitch is pulled out or addded since the pitch links are not on centerline. This alters the way precession affects the blades. Precession does NOT always work at 90 degrees. It is taught that it is always 90 degrees as a simplification.
The 72 degree swashplate offset exactly compensates for the non 90 deg. precessional response and the result is that the R-22 rotor follows the direction of the cyclic stick in a normal fashion.
Maybe Frank Robinson will post on this sunbject and shed more light on this issue.
Try-Cyclic