Originally Posted by
silverstrata
It matters not if that rear surface on the Trident is an elevator, a balance-tab, or a servo-tab - the same choice applies.
Do you fit the anti-stall aumentation system to the control column, or to the trimmer..? The diferrence being that the control column (usually) gives an instantaneous response, while the trimmer (usually) gives a slow response. So when in the recovering dive, after an incipient stall event, the stick-push will relent immediately, while the trimmer may take 10 or 20 seconds to get back to neutral.
So tell me, how long did it take for the Trident to get from full trim forward, to neutral? The 737 takes about 20 seconds, which will probably make a recovery from the dive difficult or impossible.
The Rostov incident appears to have demonstrated this problem very well. Even with the trim set to 1.5 units (instead of the normal 5 or 6 units), the FlyDubai aircraft plunged to the ground almost vertically. But MCAS does not trim to 1.5 units, it can apparently trim to 0 units. So what chance is there for a recovery, with the stab-trim at 0 units (full forward) ? I would suggest little or none....
Silver
I fear you have missed my point which was that the Trident didn't have an independent trimming tailplane with separate elevator, there was only one movable surface with a geared tab built in. In fact the pusher did act on the column circuit directly as did the autopilot, there was no provision for automatic trim inputs, there didn't need to be, just Q-feel. I fully agree though that there is a general lack of appreciation of how the trim system of, say, a 737, works, how powerful it is, and how different from the type of primary trainer, say C152 or PA28, most people trained on.