How does a helicopter hover?
A helicopter can hover without the CoG being directly underneath the rotor hub, because the rotor hub can apply hinge moments:


Fully articulated hubs with a hinge offset and fixed hubs apply direct mechanical moments to the fuselage, which line them up with the rotor angle.

The rotating blades are subject to centrifugal forces, which pull the rotor hub in the plane of the rotor deflection. As soon as the rotor plane changes as a result of cyclic stick input, the resulting rotor hinge moment will change fuselage angle accordingly, providing the desired feedback cue.
Any helicopter, regardless of the type of rotor hub, has an aerodynamic coupling between fuselage attitude and rotor attitude. A teetering rotor such as on Bell 212 and R-22 does not produce above mechanical rotor hinge moment. In flight, a helicopter is suspended from its rotor, with the Centre of Gravity underneath the centre of lift, unless the rotor can apply a hinge moment to the fuselage. With a rearward CoG and no hinge offset, the following could happen:

The helicopter has taken off vertically, nose tipped up first, and cyclic forward was input. If the rotor had a hinge offset the fuselage would tilt forward, but with a teetering hinge like in the question there is no centrifugal force acting on the hub, and fuselage position now depends only on CoG location. The upward nose angle has consumed some of the useful forward tilt of the cyclic stick. Visibility is impeded. Fuselage tilt provides no direct feedback of the cyclic position.

Fortunately there is an aerodynamic rotor hinge moment, created by the aerodynamics of flapping. The picture is from Helicopter Performance, Stability and Control by Raymond Prouty. It shows that at first, the rotor acts as a gyroscope and stays in its plane. But the blade feathering is referenced to the shaft, and angle of attack of the right hand blade is increased, left hand blade decreased. The rotor will then flap until it is perpendicular to the shaft. With teetering rotors, there is an indirect aerodynamic coupling between fuselage and rotor shaft: the fuselage attitude still follows the rotor attitude but at a slower rate.


The CoG cannot be placed anywhere, it must remain in the area where the moment caused by gravity pulling on the CoG is lower than the maximum hinge moment. But with all helicopters, there is a region of useful CoG.