I don’t claim to be an engineer nor am I an aerodynamicist however I have noted that when they switched from symmetrical to non symmetrical air foils the helicopters encountered a lot of vibratory forces mainly in my estimation from the pitching moments of the blades. A long time ago when I was in helicopter school the instructors and some of the engineers stated that the reason helicopters could only use symmetrical airfoils was that unsymmetrical airfoils generated climbing and diving moments. When the switch was made most if not all helicopters incorporated vibratory dampers to cancel some of the vibratory loads.
Ducking from incomming.
