Originally Posted by
FCeng84
. With this in mind, the nose up thrust induced pitching moment generated by the 737MAX engine is not greater than that for a 737NG. In fact, it is probably less as the center line of the larger MAX engine is higher than the center line of the smaller NG engine given their respective attachment geometries.
Hopefully it is now clear that the pitching moment of concern with the 737MAX engines that gives rise to the need for MCAS is related to the aerodynamic impact of the engine cowling location and geometry, not the magnitude nor location of the thrust vector generated by those engines.
Yes, but the 737NG already had a thrust induced pitch problem, as was amply demonstrated by the Bournnemouth incident, where an NG pitched up to 47 degrees - mostly caused by increased thrust when close to the stall. I have no doubt that Boeing had this problem in mind when they chose to implement the MCAS system. (This was sufficiently well known to already be in the simulator software, which would happily pitch you to 90 degrees up if you got too slow with full power applied.)
The problem being that the MCAS solution was ill thought out and badly designed. The system needed multiple inpututs, including airspeed and attitude. It needed greater redundancy, with another AoA sensor. It needed more refined logic, instead of running to full forward trim, which no aircraft should ever do. It needed greater error checking, to disable the system if faults or data discrepancies were detected. And it really needed to act on the elevator and thrust levers, rather than the stab (ie: reducing the thrust when close to the stall, as per the QRH recommendation).
Apart from that, it was a great design....
Silver