Originally Posted by
oggers
Where is the thrust line compared to the NG? And with the more powerful engine can you cite any data that exists about how the handling would be affected had there simply been enough ground clearance to put the thrust line in the same place as the NG?
‘Large areas of the flight envelope’ is rather subjective. Can you cite the relationship between stab trim and flight envelope parameters of velocity, load factor and altitude, that formed the basis of MCAS as it was certified?
The Max engine center line is near the same as the NG. the moment has changed as the thrust can be higher. Neither design has the engine orthogonally aligned, so the forward position of the Max would alter the arm of the thrustline unless the incidence angle of the engine was adjusted. The original angle is a compromise for performance and handling.
The geometry problem is ground clearance for installing a larger diameter fan. Moving the engine forward permits bringing the engine core upwards from where it would have been if the gear had been extended only, reducing the extent of moment change that would occur just from the thrust line. That then added the aero moment which MCAS was expected to fix elegantly in the first instance.