Originally Posted by
OldnGrounded
Yes, the diameter of the manual trim wheels changed and, yes, it was a long time ago. It's possible that there is some side loading of the jackscrew, but probably not enough to be a major factor, considering the angle it forms with the stab lever arm and the fact that the ball nut is in a gimbal ring. Yes, pilots are no longer taught the porpoise maneuver, but it has no chance of saving the day unless there's sufficient altitude AGL.
Almost certainly, the real problem with manual trimming in the sorts of situations we are considering is just that the H-stab is huge and, at some combinations of attitude, (out-of-) trim positions and airspeed, the aero loads make it either unlikely or impossible to crank those wheels enough to recover.
I did find the post- I wuz wrong- it referred to the NG NOT the MAX
They also put a damper in there as well because there was also a new trim motor.
Quote:
Regarding the trim wheels: When the NG was being introduced, I happened to be the Lead Engineer in charge of them and a whole lot of other stuff. There were some issues. The new display system created a pinch point between the dash and the wheel. We had to make the wheel smaller. And the new trim motor resulted in the wheel, which is directly connected to the stabilizer by a long cable, springing back when electric trim was used. It was an undamped mass on the end of a spring. We had to add a damper.
Result: Depending on the flight conditions, the force to manually trim can be extremely high. We set up a test rig and a very fit female pilot could barely move it.