Thanks for that, although your reply has set me on a path of further reading and not a little brain damage!
I always prided myself on knowing more about how a helicopter works, than having skills enough to fly it.
An hour in a Robbie for a birthday present, cured me of regretting not learning to fly rotary wing. I've done greasers in America in a 152 when I treat myself to a one hour 'try and see' lesson from time to time. Never really had a 'proper' lesson. But while heliboppers are fascinating and deeply interesting, as far as I'm concerned you need fourteen fingers, rubber legs and reactions like a cat to fly them.
I need to get my head round why and how the rotor articulation becomes a Hooke joint and why it can't be made into a Constant Velocity joint, which would cure the problem. I suspect greater minds than mine .........
Roger.