What an interesting discussion regarding the operational characteristics of the Robinson R-22 rotor hub.
A couple of points for thought;
The main reason for having a flapping/coning hinge offset is to provide faster rotor responses to cyclic inputs. This of greater importance on helicopters where the distance between the rotor disk and the CG is relatively short. It appears that on the R-22 the pitch link is inline with the flapping/coning hinge. On initial consideration, this would make sense. Mr. Frank Robinson has very clearly explained the considerations used to determine the delta-3 angle. I wonder if delta-3 angle was then used as the basis for arriving at the flapping/coning hinge offset?
It may be of interest to know that the R-22 uses 'control system geometry' for its delta-3 whereas the K-Max uses 'flap hinge geometry' for its delta-3. [ref. Helicopter Theory, page 239 ~ Wayne Johnson]. The 'flap hinge geometry' consists of changing the teetering hinge angle from 90 degrees (normal to blade span), to around 75 degrees. An operational difference between the two is that the 'flap hinge geometry' also has a lead-lad component, which is required to handle the Coriolis effect between the two interlocked rotors.
Dave J.
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