ORIGINAL: dick Hanson
On and on and on we go ( Da Rock got itright.)
This is like the ground effect stuff which became a farce in 3 acts.
some of the " aerodynamic"explanations were horribly off target
Dutch roll - is simply a "balancing/ rebalancing of forces" which is has just enough energy to allow an oscillation to set in
Simply taping a cup to the fuselage at some point FORWARD the CP will typically setup the problem -or at least a rudder lwagging at a fixed frequency
Old Buicks would do a "Dutch Roll which was deadly. On those old "ships of the boulevard" the combo of castor angle/ steering geometry , soft springing etc., would let the steering wheel, if moved sharply -then released , allow the car to roll in response - then the steering would self correct and the resulting lock to lock oscillation, rapidly set in. Shimmey in other cars was also a problem but nothing like the Buick issue.
same problem on ships, same on aircraft , same on control surfaces of aircraft
if the "self correcting force is "just right" a oscillation or flutter -or Dutch Roll -call it what you will , occurs.