Airflow in helicopter

[vishnu2315]

Why control surfaces are not used below rotor in helicopters?

 

[russ_watters]

Why control surfaces are not used below rotor in helicopters?

Because the rotors are the control surfaces.

 

[Baluncore]

Why control surfaces are not used below rotor in helicopters?

Because the lift on the rotor moves over the full length of the rotor so the control surfaces would need to be as big as the rotors. Rotor blades are dynamic in flight, they can rise and fall significantly. The rotor blades would collide with the control surfaces with catastrophic results.