Originally Posted by
DaveReidUK
Correct me if I'm wrong, but the coarser the thread pitch (all other things being equal), the more likely a jackscrew is to be back driveable (the spiral ratchet screwdriver principle). Is that what you're saying?
I can't see air loads on the stab being capable of overcoming the combined braking friction in the jackscrew, gearbox and actuator unless we're talking about a previously undisclosed failure in addition to the issues already discussed.
I think that’s right. The mechanical advantage of the threads is sufficient to restrain the jackscrew. Add the friction of the drive motor, and even though the nut is carried in bearings, the HS stays put? Question: Is the drive always engaged?
As to programming versus mechanical upgrades, I found nothing about “software only” to establish the new MCAS system. I got thoroughly bogged down in “Onboard programmable modules”, “Line replaceable units” and its acronym LRUs.
Sistering STS with MCAS and only one trim drive? If Trim is flight critical, (the crash suggests so), where is drive redundancy? How is one drive isolated from the other(s) such that opposite inputs would (not) stall a (single) motor?
So, somebody please tell me the HS was not Stalled? Because that is just another word for “jammed”...Is there nothing worse than runaway Trim? Perhaps an HS that cannot reverse it?
STS: Speed too high, NU..... MCAS:: AoA Too High, ND.......
Question. Was the five second pause (MCAS) put in to allow “recompute”?
Did STS see the pause as a chance to NU? Hence a game of porpoise? What are the relative velocities of NU, ND? Same? NU faster?
Unknowledgeable wants to know.