Hub
================
The field :code:`hub` describes the hub system currently leveraging much of the WISDEM way to design wind turbine hubs. This will change soon. In addition, the equivalent mass and inertia properties of the hub system can be listed in the field :code:`elastic_properties_mb`.

.. literalinclude:: ../../test/turbine/IEA-15-240-RWT.yaml
    :start-after: hub:
    :end-before: nacelle:

:code:`diameter` : Float, m
    This is the outer diameter of the hub. It is also the diameter of the circle centered at the rotor apex and connecting the blade root centers.

:code:`cone_angle` : Float, rad
    This is the precone of the rotor. It is defined positive for standard upwind and downwind rotors.

:code:`drag_coefficient` : Float
    This is the equivalent drag coefficient used to compute the aerodynamic forces generated by the hub immersed in the flow. Standard aeroelastic solvers use this parameter.

:code:`elastic_properties_mb.system_mass` : Float, kg
    This is the overall mass of the hub system, which includes the hub itself, but also the spinner, the pitch system, the blade root bearings, and auxiliary equipment.

:code:`elastic_properties_mb.system_inertia` : Array (6) of floats, kg*m2
    Mass moments of inertia of the hub system. Ixx, Iyy, Izz, Ixy, Ixz, Iyz are expressed around the hub center in hub-aligned coordinate system, which has x aligned with the main shaft pointing from the rotor apex towards the nacelle. Iyy and Izz are usually identical.

:code:`elastic_properties_mb.system_center_mass` : Array (3) of floats, m
    Coordinates of the center of mass of the hub with respect to the hub-aligned coordinate system.