Originally posted by Owain Glyndwr ...
So although the yaw damper was working the rudder pretty hard, I doubt it was really driving anything since at 40 deg AoA it was down to about 1/3 power.
Thanks for the graphics (think
HN39 posted a link to them some time back) and your explanation.
Not being an aerodynamics expert by any stretch of the imagination, I had concluded that the lateral/transverse stability of the aircraft at such a high AoA and low IAS was balanced on a knife edge, and even with the reduced efficiency of the rudder it would still be possible to induce a roll moment. You doubt that that was the case, but as I stated in my earlier post, the DFDR data is pointing toward it doing just that.
To emphasize what I am getting at, I have blown up part of the Roll trace and and superimposed the Rudder trace on top of it. In addition, an expanded (replotted) 30 second section is shown where (if the traces have been synchronized by the BEA) the rudder is constantly leading the roll and not the other way.
I'm still puzzling over the constant yaw to the right and its cause. Were the ailerons responsible, asymmetric drag, or a side-slip component? Though the more I look at it, I have come to realize that the PF had one hell of a fight on his hands just keeping the wings level, though through mostly of his own doing.