I wonder if you would care to explain to me how a rotor blade will change “its weight” with rpm?
It's a joke - according to the (special) theory of relativity the mass of an object increases with it's speed - the nearer it gets to the speed of light the heavier it becomes, so it takes more and more energy to accelerate it even nearer to the speed of light. And since the mass goes up to infinity at the speed of light py would need an infinite amount of energy to reach it. That's why no object with mass can reach the speed of light (in contrast to photons which have no mass - but then they can't slow down;-)
While, theoretically, the mass of the blade increases with RPM, this is completely irrelevant though. Even if the tips would move a the speed of sound (which is about a hundredthousand times slower than that of light) the effect would be umeasurable (heavier by factor in the order of 5*10^-11, and even less for the bits of the blade nearer to the hub which move slower) - if you hit a bug and one of it's whiskers sticks to the rotor that effect would be quite a bit larger.