To: Dave Jackson
“Perhaps the sinusoidal wave of the blade, which you mentioned, is caused by a varying lift at different blade radiuses, azimuths and forward speeds”.
Perhaps the source is the rotor's downwash striking the fuselage or tail.
Perhaps the source is ....?????
Response:
I believe the first part of your statement is correct and in addition I think the vertical movement of the blades from flapping might enter into it as well. Perhaps Nick Lappos would like to add to this.