Originally Posted by
Takwis
SOMEWHERE on this great big site, buried within one of several threads now applicable to the two MAX crashes, SOMEONE made the statement that the trim wheel was made smaller, because of a "chokepoint" (or "choke point") between the trim wheel mechanism and the new instrument panel/screens.
Remembered that post because it was a reply to one of mine, the phrase used was "pinch point" - until we have HAL to do searches looking for choke point won't find it
Link:
https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa.html#post10438165
I find they don't always work that well - gets you near the post not on it - so the relevant text is (and it's unattributed - copied from another forum):
I agree it's a flawed design. And I used to work there. I'm glad I don't now.
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.
As I said, I'm glad I'm no longer there.
Hope that helps.