This is an analysis of the variables which affect the ability to control a multi-rotor as the size is scaled up.
This will show why at some point, variable pitch must be introduced.
I hope to follow this with another article which includes Phase Margin and Gain Margin, but right now I'm trying to refresh my memory from 30 years ago on Laplace transforms and Bode Plots. Ugh!
I hope this makes some sense.