To: Dave Jackson
“The swashplate and also the basic Bell, 2-blade, teetering (normal to span) rotor exhibit exactly the same characteristic as a gyroscope. I.e. 90-phase offset”.
“All rotorheads with a flapping hinge offset have a phase offset that is less than 90-degrees. 'Gyroscopic non-relativistic rotational kinematics cannot represent this (at least not easily). 'Aerodynamic non-relativistic rotational kinematics' can.
On the typical Sikorsky with the possible exception of the S-76 the pitch horn leads the blade by 45-degrees. The control servos are offset from their direction of control by 45-degrees. When the pilot pushes forward cyclic the fore and aft servo will move down. This causes the swashplate to dip 45-degrees ahead of the longitudinal centerline. With the swashplate in this position, the advancing blade will have maximum control input and will (pick one), fly as an individual blade down over the nose or, it will dip down over the nose as a part of a collective assembly called a rotor system, with this movement, caused by gyroscopic precession. In either case, the opposite blade will be doing exactly that, move in the opposite direction. Other helicopters have different relationships between the pitch horn and the positioning of the servos but in any case when you add up the servo offset and the pitch horn lead it adds up to 90-degrees.