In the closely spaced intermeshing rotors of the synchropter configuration, any sideslip velocity through the cocked rotors creates yaw moments. A side velocity as from a gust, yawed flight, or sideslip creates a flow down through one rotor and up through the other rotor. When the blades are set at high angles of attack, an upward velocity creates an increase in rotor torque and a downward velocity through the rotor creates a decrease in torque. Because the appositely turning rotors are geared together, this torque is additive arid manifests itself as a yawing moment on the ship. In a synchropter where the outboard tips are moving aft (like a breast stroke swimmer), this yaw moment acts in a stabilizing manner and the helicopter has good directional stability.

When the blades are set at autorotative angles of attack, downward flow through the rotor tends to retard the rotor and, conversely, upward flow tends to accelerate the rotor. Therefore, in autorotation of a breaststroke type synchropter the yawing moments created by side flow through the rotors creates an unstable yaw moment which must be corrected by the addition of more fin area.