A planar flexbeam unit as interface between a rotor shaft and a multi-blade rotor, especially for a multi-blade main rotor of a helicopter. The supplemental spine fixation device includes a guide and spacer for distracting apart adjacent spinous processes and the device has hook members which hook about the first and second spinous processes. The swinging mechanism is configured to swing the needle bar in a left-right direction. Some further embodiments position drives in a herringbone pattern to redirect air flow in addition to reducing rotational-acceleration vibration interaction.