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This question is restricted to trim on the pitch axis.

Both trim tab and THS (trimmable horizontal stabiliser, a whole moving horizontal stabilizer whose movements are used as trim) are used to trim an aircraft. Aircraft having a larger speed range (e.g. jet airliners) tend to be fitted with THS whereas aircraft flying slowlier (e.g. GA aircrafts) tend to be fitted with trim tab.

Is there any aircraft type that use both? (Maybe one being a backup device)

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  • $\begingroup$ The MD-80 has a THS and uses control tabs on the elevators, but not trim tabs. Are you asking only about trim tabs? $\endgroup$ – Bianfable Nov 8 at 16:41
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    $\begingroup$ Many Messerschmitt aircraft had both, a trimmable stabiliser and a trim tab on the elevator. The tab on the 109 was simply a strip of metal at the trailing edge which could be bent on the ground for adjustment. On the 262 it was a "real" tab. $\endgroup$ – Peter Kämpf Nov 9 at 1:11
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    $\begingroup$ @Bianfable yes, only trim tabs (I didn't even know control tabs exists, thanks for the info) $\endgroup$ – Manu H Nov 9 at 6:19
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    $\begingroup$ @PeterKämpf you should transform your comment in an answer (and I'm going to search for document about Me262 controls, you just awoke my curiosity) $\endgroup$ – Manu H Nov 9 at 6:23
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    $\begingroup$ @ManuH: More research revealed that the elevator tab on the 262 is a servo tab (Flettner tab) to reduce stick forces. Trim was done with the stabilizer. Zeno's Warbirds has a flight manual from 1946. $\endgroup$ – Peter Kämpf Nov 9 at 17:27
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Trimmable horizontal stabilizer (THS) and trim tab serve the similar purpose for two entirely different control architectures:

  • Trim tab neutralizes the force on the pitch control for a reversible control system.
  • THS neutralizes the pitch position (and, in the process, the force) for an irreversible control system (e.g. hydraulically/electromechanically actuated, analog or digitally commanded).

In the presence of an irreversible actuator, the actual hinge moment on the elevator no longer matters since the elevator position is being closed-loop controlled by the actuator (provided the actuator is sized correctly, of course); but more importantly, it is no longer felt directly by the pilot. Without this direct feel, a trim tab would be more than useless.

On the other hand, in the case of reversible control with direct elevator-to-stick linkage, deflecting the stabilizer would not allow the dual objective of maintaining trim and neutralizing hinge moment to be accomplished, since a TE up stabilizer would impart even more nose down stick force to the stick. The THS is equally useless for a reversible control for this purpose.

For this reason, I would be very surprised to see an aircraft fitted with both. But maybe there are oddballs?

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I've been around light airplanes for about 45 years and I've never seen a trimable stab and trimable elevator using a tab together. The closest I can come to that is the elevator trim bungee that is included with the jackscrew stab trim on the Piper Super Cub.

The Super Cub has a moveable stabilizer that is the primary trim device, but also has a spring bungee, linking the elevator to the stab, that wants to keep the elevator in line with the stab, instead of just trailing. This gives the elevator some influence over stick free trim (you could say that it tries to help the stabilizer), improving overall trim authority over a movable stab alone.

Look at Super Cubs on the ground and you'll see that the elevator doesn't hang all the way down, but sits just below neutral. That's the bungee holding it up.

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It's unlikely that any airplane with a THS also has trim tabs. The benefit of adding them is slight (partial protection against failure of hydraulics), while the cost is extra mechanical complexity and extra drag. The extra drag is particularly important for airliners.

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