Originally Posted by
FCeng84
The stabilizer hinge line is slightly forward of the point where its trailing edge meets the fuselage. Due to stabilizer sweep angle, its hinge line is close to the center of lift such that horizontal tail angle-of-attack does not have a significant impact on the load applied to the jack screw. Due to the stabilizer sweep angle and the location of the elevators, deflection of the elevators generates a rotational torque on the stabilizer in the opposite direction. Note that all for the elevators are located aft of the horizontal stabilizer hinge line. The outboard end of the elevator is significantly aft of the stabilizer hinge line.
I used to fly skydivers in an old Cessna 182 that used stab trim. The only "locking" device for the jackscrew was the ball and spring detents on the trim wheel. The pivot point was at the aft spat well behind the center of lift. When I would youthfully speed up my decent by applying down elevator without trimming to achieve yellow line, the rotational force exerted by the elevators was enough to overcome the ball detent and I would get a sudden roll back of the trim wheel resulting in an unexpected 2.5-3 g pull up. With the 767 stab hinge closer to the center of lift, I would also expect control reversal caused by the elevators acting as servo tabs if the stab trim was mechanically disconnected.