droger

I am currently developing a rotor model for a 4-bladed, gimballed rotor for use in a flight mechanics model. I have been searching publications for a long time looking for models of a gimballed hub. There is much literature relating to teetering rotors, rigid rotors and articulated rotors but I have as yet been unable to find anythin useful on the flapping equations for a 3 or 4-bladed gimballed hub.
I have successfully derived blade element velocities and accelerations for the rotor. However, I am still puzzled how to find the gimbal accelerations. These are defined in a non-rotating frame and the gimbal is treated as a rigid body with aerodynamic forces acting on a pair of torsional springs. I need to be able to find the gimbal accelerations in order to pass into the model for the next time step.
Hence, the question is:-

Does anyone have past experience of N-bladed gimballed rotors and could give me advice or does anyone know of publications which may help me?