BP
Both A/C have "Fully Articulated" rotors but he effective hinge offset on the (various) 500 heads makes it "fly" more like a "Rigid Rotor" type head ( the aircraft in fact flys very much like the Bo105) but perhaps smoother and much faster.
The 300 head has a lot of articulation to it and to keep this under control in the lead/lag sense the early 269 series a/c used hydraulic/friction dampers.
These dampers used to wear quite a bit ..... and as a result often one damper (of the 3) would be less effective .... this would lead to one blade moving out of phase in the disc ..... not always a big problem ..BUT if the a/c also had some slightly "saggy" pneumatic u/c dampers and the pilot was a bit rough either engaging the clutch on startup OR a bit ham fisted landing the machine it would go into "Ground Resonance". The level of resonance being a question of luck for the day!
Very often after a rotor start the a/c with a low lateral vibe we would pick the a/c up go to a grassed/soft area and carry out a hovering auto ...to re-phase the blade dampers and get everything back to its "as advertised state".
The 500 series a/c having either a 4 or 5 blade head of quite a different design (brilliant for its time) was almost impervious to the "Ground Resonance". Also the u/c dampers on the 500 were of a better design tended not too leak down and thus gave less problems to maintenance.
Cheers
