enter image description hereIn flight control designs for lateral directional movement, there is a block named "gravity compensation". This block changes yaw rate measurement from "$r$" to "$r-g/Vcos(\theta)sin(\phi)$" before it is sent to the controller. How does this block change the equation of motion?

  • $\begingroup$ can you provide an image example? have you studied the equation of motion? $\endgroup$ – Federico Mar 9 at 8:54
  • $\begingroup$ I provided an image example $\endgroup$ – shooshool Mar 9 at 9:14

That term is a feedforward.
It simply makes sure that during a turn the rudder will anticipate the need for that $r$ component and thus helps making the turn coordinated.

Since the term is complete (i.e. there is also the $\theta$ component) this will work also for climbing/descending turns.

  • $\begingroup$ It looks like a feedforward. But note that it is fed to the feedback controller. If it was feedforward, it should be added to the output of the feedback. Can you provide a reference? $\endgroup$ – shooshool Mar 9 at 10:44
  • $\begingroup$ @shooshool no, it is a feedforward. the fact that is added to $r$ instead of the rudder command does not change its nature. source: I've implemented it several times on our research aircraft. $\endgroup$ – Federico Mar 9 at 10:56
  • $\begingroup$ Should this feedforward be considered when the controller block is being designed? Or the controller is designed without considering the effect of feedforward and then the feedforward is added? $\endgroup$ – shooshool Mar 9 at 10:58
  • $\begingroup$ @shooshool if it is there, usually the controller is designed assuming that the feedforward is working as intended, i.e. lowering the load on the controller, but that's a different matter not for this stack $\endgroup$ – Federico Mar 9 at 11:05

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