Originally Posted by CV Donator
Its quite frustrating there doesn't seem to be one definitive answer to the dutch roll question. My understanding was that it was caused by stronger lateral stability and relatively weak directional stability. Aircraft yaws then rolls due to faster moving wing plus increase projected span on the outer wing, the tailfin then acts like a wind vane yawing the aircraft back to zero slip this then causes secondary roll, the aircraft rolls beyond zero slip in the opposite directon and the process is repeated. Also at play I thought was the dihedral effect of the lower wing increasing lateral stability.
The "one definitive answer" can be found by solving the equations of motion for an aircraft, decomposing into the (assumed) independent longitudinal and lateral/directional components and then identifying the second-order roll-yaw coupled motion in the solution.
It involves all six derivatives in the roll/yaw axes to determine the frequency, damping, roll-ot-yaw ratio and the phasing of the roll and yaw motions.
You don't need one derivative to be "strong" or "weak" to have Dutch Roll - all that specific values do is change the nature of the mode, not its existence.