737MAX Stab Trim architecture

[gums]

Salute Jim!

Worth talking about the elevator authority and such.

High "q" will definitely make that big stab overpower the much smaller elevator.

Apparently, this bird ( 737) seems to act like most of us expected in the old days and even today until they let us fly a plane with negative or neutral static stability[see added below] . We trimmed to reduce control pressure/movement. That got you back t the original AoA/speed. So you could have a lot of elevator deflection but the trim operation would allow less and less control pressure until you reached the desired trim for speed/AoA. And then we had STS, which trimmed the stabilizer without pilot input. Huh???? This ain't no Airbus fly by wire FLCS. But rational was to tell the pilot ( I use pilot to assert whoever was in charge of moving controls), he needed to trim for the new speed/AoA. What airplane have they flown that did not need a new trim after changin speed/AoA?? Do they need to be "reminded"? SHeesh.

And then we get another tweak to the plane's flight control system.. MCAS. And its operation and such are not well known by the rank-and-file aircrew. How much interplay between MCAS and STS and the articicial pitch "feel"?

Gums sends...

ADDED: I wish to clarify my assertion about static stability or speed stability. Some folks think the FBW Airbus planes have neutral speed stability. So most of the time speed is controlled by power. The fact is that at least the AB330 that went into the ocean (AF447) showed very good stability and fairly benign stall characteristics. No violent wing rock or buffet. The stall "protection" was inhibited due to the low airspeed value feeding the flight control computers, so HAL did not keep the pilot from commanding back stick and the stabilizer from trimming to full nose up. From reading about the Concorde, which had a lotta fly by wire, even it had conventional speed stability.
The Boeing STS is a funny way of telling pilots they have to re-trim if speed changes. Duhhh? Oh well, I would rather have the plane try to get back to last trimmed speed and I can trim up or down to achieve the new desired climb angle or new airspeed//AoA. And remember that we' re really trimming to AoA. I do not unnerstan moving a large control surface to tell pilots they need to trim versus using the "feel" system that the plane already has and has done fine for decades.