>>539379829
i believe the image you posted is for tandem-rotor aircraft. for >>539376901 picrel i believe is more accurate. remember that the rotor and blades are imparting a "spin" to the aircraft already. the second set of blades spinning in the opposite direction negates that "spin". so if you want to perform yaw on a co-axial helicopter, like the one depicted in >>539374756, you need to reduce the effective spin one of the the two sets of blades applies (by reducing speed of one set or by reducing pitch). for more information i found this stack exchange answer that covers this perfectly: https://aviation.stackexchange.com/questions/22707/how-does-a-helicopter-rudder-work