Mass is not linearly proportional to length, because a longer rotor needs to be a lot heavier to be structurally sound. A uniform rod is not a good analog for a

Mass is not linearly proportional to length, because a longer rotor needs to be a lot heavier to be structurally sound. A uniform rod is not a good analog for a rotor blade. It's not a far fetched idea to think that the mass is cubically or at least quadratically proportional to the length of the rotor. Unfortunately I can't remember the source where I saw the 5th power figure. In addition, the aerodynamics of a rotor don't scale up linearly either.