To:212 man et al.
On the 212 the lift link is positioned left and forward of the mast centerline. When lift is applied the transmission will rise and due to the positioning of the lift link it will move in the same vector (left and forward). Because the 212 has a two blade rotor system each time the blades are aligned with the longitudinal centerline the transmission will fall in relation to the fuselage. This downward movement of the transmission will react against the fixed lift link and the transmission centerline will move to the right and rearward. As the blades pass the longitudinal centerline and lift is generated the transmission will rise in relation to the fuselage and react against the lift link and move forward and to the left. Other things such as worn mounts will add to this phenomenon.
The reason pylon rock is not present on the 412 is because of the four blade system that is constantly lifting. The 412 will however move to the left and forward when lift is generated and it will essentially remain in that position unless there is maneuvering and then the transmission will move in an orbit in relation to the optimal centerline of the mast. It is this movement on both airframes that can cause the separation of the drive shaft if the movement is excessive.
This vertical beat on the 212 or even the Huey or 206 was the reason for the development of the Nodamatic Suspension system. The transmission moves up and down in relation to the fuselage but the Nodamatic nodal beams and weights absorb the vertical beat. The pilots and passengers experience a very smooth ride and the transmission is moving up and down at a rate of two times the rotor RPM.
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The Cat