I'm asking about general aerodynamics for under-wing twin-jets – I'm not after information/speculation on the Max 8 crashes/systems, but I mention the crash below because of what I see as an unclear (to me at least) explanation:
All objects on an aircraft placed ahead of the Center of Gravity will contribute to destabilize the aircraft in pitch.
- But as one commentor wittingly pointed out, wouldn't the fwd engine also move the CG fwd.
[G]enerating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA).
- I read this as insufficient pitch authority, not pitch instability. Going by the text above, I would also imagine the destabilizing force to be a drag from the larger nacelle's bottom, not lift. For example, the relaxed pitch stability of the MD-11 warranted an LSAS system, but not a special anti-stall system.
I tried to look for an official explanation for why MCAS was added to understand the general aerodynamics, but the prelim report doesn't mention it.
I've presented what has me confused, but the question is the one in the title, wrt general aerodynamics, not 737 Max or MCAS.