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> But at the same time that trim system is, by design, not strong enough to overpower pilot input to the other control surfaces.

That is incorrect for the 737 and many airliners. Elevator input is way less strong than trim. Trim moves the entire surface, not just the elevator control surface.

I had the same misconception, my brain was translating GA aircraft knowledge to airliners.

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The GA Aircraft; Cessna 182B has Stab trim.

Most light GA aircraft have a trim system that works by using a smaller trim surface to aerodynamically deflect the larger control surface. In such a system, the horizontal stabilizer has a fixed relationship to the fuselage. Later 182s definitely have this system (I owned a 182K for 16 years).

Some light GA aircraft have systems with jackscrews that deflect the horizontal stabilizer as in airliners. These systems are more efficient aerodynamically, but can overpower pilot input, at least in theory. The aero trim system (in prior paragraph) cannot.

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