Originally Posted by
edmundronald
My belief is that it’s not a simple curve, but depends on some additional factors eg. thrust vs. airspeed, and extant stab setting, and has some really nasty hidden non-linearities FOR SOME PARAMETER VALUES.
In fact the pitchdown on nose down might be even more lethal than the pitch up on nose up.
Edmund
I fully agree. As I said in a previous post, I would be very interested to see the relation between the engine nacelle drag/lift forces and the CG of the aircraft.
Normally the moment arm from engine nacelle forces around the CG would be small, and the force would be expected to act BELOW the CG, thus counteracting pitch up.
Looking at the Max profile on the other hand, I would be tempted to say that the higher/forward position of the engines could cause these forces to act ABOVE the aircraft CG at high AoA, which would give a nasty non-linear feedback with AoA.
Imagine if there's a part of the envelope where the nacelle force moment arm transitions around the CG.. Maybe this happens for a combination of aft CG and high AoA. Instead of designing away the problem, B decided to block pilots from entering that part of the envelope --> MCAS.
Disclaimer* I'm a researcher in aerospace engineering mechanics (fluid/solid interaction), not a pilot.