The question isn't if they didn't know, it's if this is an unusual level of instability for an airliner.
>We're talking 'stability that adheres to control forces required by regulation' rather than 'F-117 drop out of the sky' instability.
Hopefully yes, but we don't know how much instability there is. If you assume the answer there's no point having the discussion.
Because we don't. You've only corrected a strawman, that we know this plane isn't a fully aerodynamic unstable design like an F-16. No one thought that.
I never even specifically said aerodynamically unstable, just that we don't know the level of instability MCAS is correcting for to know if it is unusual for an airliner design. From what I had read I had assumed it was actually a power-on issue and not aerodynamic. But as it turns out the issue is indeed apparently aerodynamic from the engine shape generating more lift at higher angle of attack and thus leading to pitch up.
And no, we don't know. We the public at least. We don't know how big the flight envelope is where MCAS is needed or how much of an issue it would be if MCAS didn't exist. From public information we don't know if without MCAS the plane wouldn't enter an unrecoverable pitch up attitude in normal flying conditions. That's not knowing if the plane isn't inherently unstable.
I’m not responding to a straw man, I’m responding to what you wrote. If it’s not what you meant, well, I can’t really do anything about that.
Hopefully yes, but we don't know how much instability there is. If you assume the answer there's no point having the discussion.
I was making the point that we don't know what was actually certified. Having F-117 level instability is obviously not the case but apparently the instability it does have is actually aerodynamic so your argument doesn't even work. The actual opposite is happening. The non-fly-by-wire design was modified with an automatic control adjustment to fix an aerodynamic issue. All your argument proves is that the MAX didn't magically turn the 737 into an inherently unstable design which is not relevant to the issue of if the MCAS is covering up a large or small instability.
- Boeing did a good enough job with the airframe that the plane flies mostly fine but there are no miracles and some specific angle-of-attack and airspeed situations make it fall outside the rules.
- To bring the plane back into compliance they implemented a fairly simplistic solution in MCAS. Because the situation that is being fixed was fairly benign they didn't engineer it with triple redundancies.
- The lack of redundancy was understood to not be a big issue because the worst possible outcome is runaway trim and that's something pilots already train for anyway.
- The MCAS runaway trim presents itself in such a unique way that even experience pilots that are already warned about issues with the plane fail to diagnose it.
It's in this context that I would then like to know how unusual this situation is. If modern airliners all have these kinds of issues solved by control software then this is just another failure mode that needs to be fixed. If instead it was indeed unusual to fix the aerodynamic issue with control systems then the discussion about Boeing forcing through with the 737 instead of redesigning becomes more important.
McDonnell Douglas also implemented something similar one of their DC' family of jets. I believe it was either the 9, 10, or 11. In that case it was to accommodate a smaller tailplane to decrease drag.