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The Bombardier C-Series aircraft has a movable horizontal stabilizer. It also has Trim Up/Down (discrete) switches in the cockpit.

  1. Is the aircraft also equipped with trim tabs?
  2. If so, when pilot adjusts the trim using the trim switches, which surface moves - horizontal stabilizer or trim tabs?
  3. If an aircraft has both trim tabs and movable stabilizer, when are the trim tabs used for trimming?
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  1. Is the aircraft also equipped with trim tabs?

From the images available online (this is a youtube screenshot, click it to see the larger version), no. And see point 3 on why I was not expecting any different.

Bombardier CS300

  1. If an aircraft has both trim tabs and movable stabilizer

I do not see the need of such a solution, a trimmable stabilizer is already optimal, adding trim tabs would increase the complexity of the system with no significant benefits, as the use of tabs increases drag, something that a THS does not.

I do not know of any aircraft that uses both THS and tabs, but, should one exist, I presume one would use the tabs only if significantly faster than the THS actuation system, allowing the aircraft to be trimmed more rapidly, but afterwards the THS would take care of the trim allowing the tabs to go back to neutral and reducing drag.

This solution would be hardly beneficial, since commercial aircraft (as the one that prompted your question) do not preform manoeuvers that require such fast (and eventually frequent) re-trimming.

In addition, as GHB has pointed out in the comments, the elevator is already able to take care of fast transients, the trim tab would only provide unneeded complications (in the design, the maintenance, the control).

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  • $\begingroup$ What would then be the difference between a fast trim tab and an elevator? $\endgroup$ – GHB Mar 30 '16 at 20:50
  • $\begingroup$ @GHB practically, not much, except the probable authority: the elevator would be able to provide much larger forces/moments. I've added it to the answer, thanks. $\endgroup$ – Federico Mar 31 '16 at 6:42
  • $\begingroup$ "...the trim tab would only provide unneeded complications (in the design, the maintenance, the control)." One advantage I can see would be the ability to use the tabs as a secondary means of moving the elevator in the event of a complete hydraulic failure, like the B737 does. $\endgroup$ – Sean May 24 '18 at 22:22

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