Originally Posted by
edmundronald
...The suspicion is that MCAS is there to keep the MAX centered in an envelope where it appears linear, but that without MCAS it might get into states where it would be really hard to control (except for Chuck Yeager and you). The unfortunate joke is that the extant MCAS took several airframes into states where they were hard to control.
I’m sorry if the above is erroneous or unclear, my opinions are usually worth exactly what people are paying for them...
Merry Xmas
I suspect that in the fullness of time, when modelling of the flow is conducted by some august body with unsteady modelling code, that the effect of the cowling will end up being noticeable but not significant in itself, that MCAS the cure is worse than the risk that it protects against. My estimate is that it will not have ever resulted in an unstable condition, that the underlying effect was notchiness of the nacelle acting as a lifting body with vortex structures over the wing, and that the vortex interaction on the wing is a more significant component of the pitching moment; the combined effects of planform increase forward of the cg, vortex structures over the wing increasing lift inboard (forward shift of Cp and reducing Cm on a swept wing) and increased downwash at the tail from the inner section of the wing arising from the nacelle vortex interaction with the wing at high AOA. With all of those effects, still suspect that the total effect was modest and never resulted in a pitch up. I'll wager USD100 on that to the first DNS/LES modelling that shows differently.
All that really means, the cure may well have been far worse than the symptom.