Originally Posted by
Dave Therhino
You have this backwards. My understanding is that manually controlled electric trim operates at high speed with flaps down and at low speed with flaps up. MCAS operates the trim at high speed.
Do you have a reference for that ?
On the NG (which of course doesn't have MCAS), low-speed yoke trim (i.e. with flaps up) is the same rate as high-speed A/P trim. High-speed yoke trim is 3x that rate and low-speed A/P trim is half the rate of high-speed A/P trim. I would have thought that MCAS would trim at the A/P rate, but I haven't seen that documented anywhere.
There's no gearbox in the stab trim motor.
Good description here:
B737NG Flight Controls