I am going to use the Aerospace Blockset.
Please refer to:
http://www.mathworks.it/help/toolbox/aeroblks/customvariablemass6dofeulerangles.html
This block takes into account a body with variable mass, thus a mass
flowrate and a dI/dt are reported into the equations.
Anyway, in a general approach, the mass flow rate could change CoG
position of the body.
How does this model approach this aspect?
From a physical point of view, the body can be assumed rigid? In fact
there is a relative velocity among the Cog and the other points of the
body.
Best Regards