Originally Posted by
Vessbot
This is the fundamental basis behind aircraft stability.
A badly trimmed aircraft is not an unstable aircraft.
You can aileron trim the heck out of a 737 autopilot and it won't move at all the aircraft as the autopilot will counteract. But it ain't going to be staying there when you disconnect the autopilot because the aircraft is actually out-of-trim. It is perfectly stable though, it will violently look for it's new balance.
It's on this basis many people claim the 737 is an unstable aircraft. It is not. It is a stable aircraft with a control issue. Before anyone jumps on that 737 bandwagon again (we already did I noticed). Pitch-power couplings don't make an aircraft unstable, it does shift the balance. We already learn this ie on a Cessna with something called P-factor. Increasing thrust does not make your aircraft unstable, but the balance changes (albeit in a different axis on the Cessna).
And that's why the eyes need to stay on the attitude. Because "control" of balance is our responsability and we call it trimming. And you have a PM to act as a back-up primary back-up. You do realise the PM has to do deviation callouts? Because yes, eyes and brains of the PF wander around sometimes... (and autopilots disconnect... or get bad inputs...)
Keep it simple people, stop mixing around to complicate... I’m off to the bar now...