Hovering in the Wings & Wunper: Thanks for the in-depth questions and answers.
There is more to be uncovered about the sources of rotor induced vibration, but to deviate slightly, for the moment;
At appears that the aerodynamic sources of the N-per-rev vibration, which are summed at the hub, are only one half of the problem. The other half is the dynamic resonance(s) that amplifies this vibration. If it is assumed, for this argument, that the sources of this vibration cannot be reduced, then it would appear that a reduction of the resonance is preferable over that of offsetting the vibration.
Much is done to assure that the components within the fuselage are 'out of tune' with the vibration. The blade is the primary source of aerodynamic vibrations, so what is done to assure that the blade does not resonate?
In this regard, I would think that a highly rigid blade would be advantageous since its frequency will then be far above those of the sources of the vibration. Lu previously mentioned " ... undamped sinusoidal wave that travels down the blade from the tip to the root. ". A rigid blade should result in a local disturbance at one blade element being greatly dampened by the other elements of the blade, before it get to the hub.
[ 15 January 2002: Message edited by: Dave Jackson ]</p>