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SUMMARY: What if the yoke didn't require constant pressure, as is the case with the current "trim" function?

In all cases that I know of, airplanes have had the yoke (which you need to apply constant pressure on) and trim (which you don't) separate. The yoke is used to short inputs, such as a roll or a pitch down, and the trim is used to maintain the aircraft in a specific attitude, given the changing nature of center of lift and gravity.

But I do not understand why it is necessary for them to be separate. Trim can do (almost) everything a yoke can. Would it be a good idea to combine the two?

Some advantages:

  • simplification
  • Safety; fast reaction to sudden trim changes (such as part of wing or empennage breaking off)

Some drawbacks:

  • trim does not center itself, so there's that inconvenience
  • increase chance of wild maneuvers if left unattended while deflected
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  • $\begingroup$ "which you need to apply constant pressure on" ummmm, no. Oh the golden days when the instructor noticed I had not trimmed the plane to zero stick force. Instant slap on the wrist followed. $\endgroup$
    – Jpe61
    Sep 26 '20 at 20:09
  • $\begingroup$ @MichaelHall tried a fix. better now? $\endgroup$
    – Abdullah
    Sep 27 '20 at 5:26
  • $\begingroup$ @MichaelHall ah, well, I don't know everything :D. I'm editing agin $\endgroup$
    – Abdullah
    Sep 27 '20 at 14:37
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    $\begingroup$ Note that Airbus FBW aircraft have an Autotrim function that does pretty much the same as what you’re asking about. $\endgroup$
    – TomMcW
    Sep 27 '20 at 23:42
  • $\begingroup$ The trim can't really do anything the yoke can do. The yoke controls the elevator while the trim wheel controls the much smaller trim tab. Flying by using the trim tab is very inefficient $\endgroup$ Sep 29 '20 at 22:33
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I think you misunderstand what the purpose of trim is, which is to change the attitude of static stability.

The yoke (or stick) is the primary flight control. Virtually all changes in attitude will originate here, and any temporary changes also end here. If you take your hand off, the plane returns to the original attitude.

When you want to make a permanent change, you set the new attitude using the yoke (or stick) and then trim until the required pressure goes away. When you take your hand off the yoke (or stick), the plane remains in the new attitude.

Some planes do have an elevator trim control on the yoke (or stick) to make things easier on the pilot, but this doesn’t change how it is used. Some planes also have rudder and aileron trim controls; I’ve never seen those on a yoke (or stick), but I’m sure someone, somewhere has tried it.

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The advantage of NOT having the trim controls on the yoke is that its far simpler, mechanically. For instance the elevator trim on a Piper Cherokee is basically just a wheel attached to a cable running straight back to the trim tab. Imagine the Rube Goldberg design that'd be needed to put it on both control yokes. (Of course if you have more complex "fly by wire" implementations, as in airliners, it's pretty easy to put the control button wherever you like.)

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