Virtually all modern helicopters use assymetrical airfoils on the blades, with variable airfoil sections a so that the root is different that the tips.
I was unaware that modern helicopters used asymmetrical airfoils. I believe this was first tried on the Cheyenne helicopter and I also believe it was the cause of that helicopters demise. The rotor head was rigid and the blades were relatively stiff by comparison to most helicopter blades and the constant change of the airfoil shape led to instability of the blades because of the pitching moment caused by the constantly changing unsymmetrical air foil sections. Assuming we can all agree on gyroscopic/aerodynamic precession the blade phase angle which was supposedly 90-degrees could vary all over the place so that if the pilot pushed forward cyclic the helicopter would most likely roll to the right and not to the same degree depending on weight, air density and airspeed. In some cases it would result in divergence resulting in fuselage contact. It took several years and several major design changes to the flight control system to solve the problem. The solution to the problem was so complex that there were almost 100 single point failures that would result in loss of control. As a result of this the Army cancelled the program making way for the Apache.
