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Old 11th Apr 2019, 04:28
  #190 (permalink)  
Dave Therhino
 
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Originally Posted by 737 Driver
Related question: The 737 has a single stab trim motor that operates at two speeds. The yoke trim switches actuate the trim motor in the high-speed mode. The MCAS (I believe) uses the low-speed mode. Is there a difference between the available torque in high-speed vs low-speed modes? For example, I have a two-speed electric drill that can stall out in the high-speed setting, but will continue to operate at low-speed. If the stab motor suffers from a similar phenomenon, I could see how the MCAS could function while the pilot-commanded trim would not.
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.

Your drill (if it's like my battery powered Makita and my corded Milwaukee) actually has a gear ratio change when you go from low to high range. I don't think the stab motor speed difference is achieved that way, and instead is done electrically in some manner.
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