Hi roulis
I am holding that resonance definition of "dutch roll" from my automation teacher, an engineer working at the last French projects.
Whilst I hold to that I got from my professor and all the reports I read on the subject as a young man!
Look roulis, this is mainly semantics and I don't wish to prolong the debate. I learned a long time ago that if you express your arguments in a firework display of Greek letters and differential equations then 95% of your audience will not understand you and the other 5% will not believe you, so let me say my piece once in plain English and then go back to lurking.
All aircraft have a dutch roll mode but not all aircraft have a dutch roll problem.
Lateral stability has three parts (OK, solutions to the equations of motion if you must ...)
a) Roll damping - always a subsidence
b) Spiral stability - either a subsidence or a divergence but never an oscillation
c) Dutch roll oscillation which may be damped or undamped; described by three parameters - frequency, damping and roll/sideslip ratio.
All of these are excited by manoeuvering the aircraft or by turbulence.
And suddenly he had a thought, stopped one second, and said "Dutch roll is resonance tween the first degree system of roll of the aircraft, and action of pilot....
There I think he was wrong, if only because one can't get resonance in a mode with only one degree of freedom. Dutch roll is an oscillation that can be, and is, triggered by sideslip with no pilot action necessary.
If the dutch roll is well damped then there is no problem, but if not and particularly if the roll/sideslip ratio is high then if turn coordination is not perfect applying aileron can start off an oscillation which yes, does affect the roll response. In extreme cases it can generate a hesitation or even a partial reversal in the bank angle response. At high AoA if the aircraft rotates around the fuselage axis then sideslip may be generated anyway unless some rudder is applied at the same time.
In other cases it becomes difficult to maintain straight and level flight.
I showed the animal,his position, speed, acceleration, counted seconds in my head, reckoned two easy differential equations in my head and piloted the result (nothing to do with the above B727 rolls described method).
And five times ago I was able to stop the "dutch roll" (in the sense of my former learjet instructor and the books) with a bank which was never more than 30°, in less than 30seconds, and never lost more than 1000 ft.
If you can solve two differential equations in your head whilst at the same time flying an airplane then you are a better man than I
But in the end, were you doing any more than applying the process that Chris Scott (I think) described earlier - applying corrective aileron at the correct time in the roll?
Machinbird who had written about PIO in the AF447 thread suggested me to read Mc Ruer's book about PIO and other APC.
Yeah - all good stuff isn't it
So I stay with my teacher's definition of dutch roll. I don't deny the roll and yaw reciprocity which conduced to the yaw damper conception, present on all airliners of course.
And I will stay with mine, but as I said it is mostly semantics
The failure of the yaw damper is the first cause of dutch roll or aggravated roll and yaw oscillations. If the pilot is not able to stop them quickly which is the most frequent case, the bank will really increase, also in the case where we still are in a first degree system in resonance with pilot's "normal" inputs...
Like I said, no resonance in first degree systems....
About the stability of the "A300", the APA document refered by misd-agin is not so optimistic with the "FBW" technology version of the A300-600R. In any case iit needs its yaw-damper is functionning.
Errrr - what FBW technology on the A300?
For the defense of some aircrafts major manufacturors I would like to remind that oscillation computation means are relatively recent.
Well we didn't have today's computing power, but we were calculating dutch roll contributions to lateral behaviour half a century ago
