Are helicopter with coaxial rotors equiped with blade flapping mechanism?

Question

Helicopters with coaxial rotors such as the Ka-27 don't need mechanisms to overcome dissymmetry of lift as there is advancing blades on both sides of the helicopter. A common mechanism to overcome the dissymetry of lift on classic helicopters is the blade flapping as described here.

I see no need to introduce blade flapping on coaxial rotors helicopters, but there can be other reason to keep it I don't know.

Are helicopters with coaxial rotors such as the Ka-27 fitted with blade flapping mechanism?

Answer 1

Yes and no, but mostly yes, especially the Kamov family.

Here's a picture(Wikipedia, CC-SA) that shows the (pair of very complex) flapping mechanism on Ka-27. Even though two rotors together should be able to balance out the asymmetric lift, the rotor hub and rotor for each individual rotor isn't rigid or strong enough for handle its own asymmetry (when it happens accidentally, e.g. the receding blade stalled, the receding blade of the top rotor will bend down and hit the advancing edge of the bottom rotor bending up and cause a catastrophic failure, e.g. Ka-50 had a series of rotor collision accidents).

However, there are rigid rotor helicopters and these don't bend nearly as much and don't need to flap, but none of them are among the Kamov lineage.

This is especially useful for high speed helicopters (e.g. Sikorsky S-97 Raider) because no amount of flapping will generate enough lift before stalling to cancel out the lift asymmetry, for the receding edge is too slow, so it has to let each rotor remain asymmetric and let the two rotors cancel each other.