Miami Dutch roll • Oct 4, 2013 1:47:44 AM
I say it again AA587 was steady in the turbulent airflow before the unappropriate sharing actions on pedals. Miami is confirmed to have started as a dutch roll due to yaw A/P failure.
A real dutch roll is an OSCILLATION from one side to another with increasing bank due to resonance.
Despite you have a yaw movement in the dutch roll, the names says it well it s a ROLL oscillation, to be corrected with the stick not with pedals.
Don't confuse dutch roll with a low prestall flight that you control with rudder. A stall probably will evoluate to a spin on one side not with that bank oscillation from one side to the other.
Spiral is another situation with bank on a single side.
Lazy eight is already a little different : the dynamic oscillation is present but stays on the step of resonance. The flight remains not really unstable.
In the dutch roll the pilot has a very active role when he flies as learned.
Controling a dutch roll gets really scabrous if you feed his closed loop with energy: and we know that reserves of energy are unlimited so long te plane is not on the ground and stopped (potential and kinetic energy). If you "play" a little more with oscillations or configration or thrust, you continuesly tansfer energy bags... that is very bad! If you know nothing about dutch roll, but have identified it, and have some room under you, the best is to put feet on the ground and hand on the knees : not very easy for a pilot in emergency!! If you are near of the ground, first go around, get altitude...
I suppose you had already applied oscillation abnormal procedure (yaw damper off/alt probably).
Using only the half, or 20%, of the control is not sufisant to overcome quickly a dutch roll. You have to use controls as some exact moment and at exact speed, after you leaved an exact number of seconds action on controls.
The dutch roll closed loop may be controled if you do not pull your plane in furious dynamic. Help the plane to find back quietly his first (!!) order natural oscillation (stopping to shake it!) , don't try to compute in your head when piloting an emergency a second, third, fourth degree system you builded yourself by that shaking : it is just impossible.
Let us jump here equations which don't figure in the well known n/speed stall and gusts enveloppe. But sailors know something looking like dytch roll, the French name is "roulis rythmique". Another similar dynamic is that of the toreador : banderillas are used to oblige the animal to use only first degre movement.
The dynamic of the dutch roll affects not only the position and attitude and bank of the dutch rolled pkane, but also the airflow around the plane, resulting in the very strong effect catching the plane as in a net and doing very difficult some movements. Miami report shows that phenomena which has to do with our bad knowledge of ..theory of lift.
Originally Posted by roulishollandais 26.sept2013 this thread #27
We have two very different situations :
- The flightAA587 wastooken in a heavyand quick wake turbulence and the first officer did that violent pedal sharing very quickly - probably the captain had feet on the ground and could not avoid his FO pedaling quickly enough. It is a non pilot induced big oscillation of the airflow where the A300-600 had a stable dynamic, followed by a pilot action near of shocks givingexcessive conventional aerodynamic forces.
- In the both cases with Yaw damper failure, the possibility of DUTCH ROLL is important. You avoided it on your B727. Your friend and his Captain had less chance and developped the dutch rolll which is a resonance between the airflow movement around the whole aicraft and action with roll and/or rudder of the pilot to stop that PIO -inadequatlybecausethedutch rollisnot taughtto pilotsnoredescribed in ATPL books, where the problem is described as non existing with the yaw damper . But dutch roll may start by other initial disturbation - pushing one pedal violently (..in a sim issafer ) - and the pilot feeds himself the resonance acting on the stick and pedals AT THE WRONGMOMENT ANDWITH INADEQUATE SPEEDS. A good aerobaticflightculture may avoid/correct that resonance without equation, but it may be solved, in flight, by equations too.