PixelFlight wrote:Chemist wrote:Contrary to the hyperbole we've read in these threads, there's never been any documented evidence that the MAX pitches up, or is unstable or uncontrollable.
The evidence is that MCAS commands nose down stabilizer to enhance pitch characteristics with flaps up during elevated angles of attack. (according to Boeing presentation to FAA).
Why do you think a nose down command is required, if this is not to fix a nose up pitch characteristics ?
I think the confusion is the difference between a "nose up pitching moment" (i.e., a torque applied about the CG in the direction that would raise the nose) and the aircraft actually pitching up. During normal trimmed flight, the nacelles and the horizontal stabilizer usually have a nose up pitching moment to balance the nose down pitching moments from the wing and the CG being forward of the neutral point, i.e, trimmed flight is a net zero pitching moment. Because the MAX nacelles contribute disproportionately to the nose up pitching moment at high AoA, the horizontal stabilizer compensates by reducing its AoA, which causes the pilots to have to deflect the elevator further to maintain a net zero pitching moment, thus generating the requisite stick force gradient . This is the key misconception. The stab doesn't move because it needs to point the nose down.