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In some fly by wire systems I found that there is no trim in the traditional sense. I believe it is because the forces that pilot feels on the stick are artificial. I was told that those fly by wire systems has elevator offload functionality that moves H-stab.

  1. Can anyone explain how elevator offload functionality is implemented?

  2. Does the artificial feel system generate force in response to airspeed and vertical acceleration? (like making pilot push harder for every knot/every G away from the trimmed state?)

  3. Is trimming necessary for FBW systems and if so How does the fly by wire system implements the trim?

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  • $\begingroup$ From Lufthansa Technical Training Manual for 777 > Elevator Offload Function Operates only in the AirCommands to Determine when the Elevator is not at the Neutal Position for more tahn two seconds minimum.Commands the Horizontal Stabilizer to move as a Function of Airspeed. The Movement of the Horizontal Stabili-zer then causes the Elevator to move to the Neutral Position $\endgroup$ – GHB Mar 8 '16 at 17:57
  • $\begingroup$ Seems like an answer to me, @GHB! $\endgroup$ – FreeMan Mar 8 '16 at 19:19
  • $\begingroup$ Hi @FreeMan, I am quite new, I tend to agree but is a partial one though! What should be done in these cases? $\endgroup$ – GHB Mar 8 '16 at 19:21
  • $\begingroup$ @GHB - make it an answer. If others feel it's good, they'll up-vote you. if they feel it needs work, usually you'll get some comments on how to improve it. Occasionally, you'll get a drive-by down-vote with no idea why... $\endgroup$ – FreeMan Mar 8 '16 at 19:23
  • $\begingroup$ @FreeMan Thanks! $\endgroup$ – GHB Mar 8 '16 at 19:24
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Regarding the first point, from Lufthansa Technical Training Manual for 777, page 30:

Elevator Offload Function Operates only in the AirCommands to Determine when the Elevator is not at the Neutral Position for more than two seconds minimum.Commands the Horizontal Stabilizer to move as a Function of Airspeed. The Movement of the Horizontal Stabilizer then causes the Elevator to move to the Neutral Position

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  • $\begingroup$ That's a long document, if you can indicate the page number, that would be helpful. $\endgroup$ – FreeMan Mar 8 '16 at 19:32
  • $\begingroup$ @FreeMan Thanks, done! $\endgroup$ – GHB Mar 8 '16 at 19:43

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