Originally Posted by
PerPurumTonantes
A motor which is forcibly stopped can pull a huge amount of current. Depends on motor type but for old fashioned non-electronic controls can be 20x full speed current. Of course we don't know the motor type or controlling electronics. Anyone?
Yes, so it will heat up, and eventually the wiring will burn up / melt /otherwise fail. But that will take a while. Being essential, that motor will be dimensioned rather larger to avoid such problems. And we know that on the Lion Air flight, the trim motor worked much more than in Ethiopia, and there was no question about it overheating or being disabled.
Also DaveReid's post above about motors stopping if they meet resistance.
No, that's not what he said. He said that the motor will be "
disabled if resistance is detected at the cable drum.", which is different from just meeting any resistance to its motion, e. g. resistance from the jackscrew nut.
I can't see any reason for the 'blips' in nose up trim other than pilot trying it and it not working/ not appearing to work. Why else would you release the switch when it's the one thing you're focussing on, the one thing you know you need?
We don't know what they were focusing on at that time. Possibly not trim, but just pulling together. Just before the blips the "
Captain asked the First Officer to pitch up together and said that pitch is not enough." And pitch trim did work, it moved from 2.1 to 2.3 units. I cannot comment on how much that would be felt in the control column.
Bernd