PPRuNe Forums - View Single Post - MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures Mk II
Old 24th Dec 2019, 17:29
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MechEngr
 
Join Date: Oct 2019
Location: USA
Posts: 0
Originally Posted by clearedtocross View Post
Nicely explained, MechEngr, but that's the trim stability of a glider... Now add two large bonks with thrust/drag not vectored through cg and in line of flight, and you get another big factor influencing pitch moments. As we do not know in what flight regime(s) the unacceptable pitch up tendency occurs, the power (or idle drag) of the engines add to influencing factors you mentionned. What I cannot figure out - maybe some of you can - is the fact that the unwanted non-linearity does not occur with flaps/slats slightly extended.
MCAS does not respond to any of those things, which all commercial jets have and for which pilots already have to compensate, and aren't fundamental to understanding MCAS. Landing gear, the rudder/vertical stabilizer, flow around the fuselage, wing downwash affect on the horizontal stabilizer, cargo/passenger loads, compressability effects, et al, are complicated interactions when a simple explanation was wanted.

I expect that with flaps/slats that the pitch-down increases so much that the non-linearity contribution from the engine nacelles is back to being too small a relative contributor to notice.
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