Reply to post: Re: Alternate 737MAX design kludge

Deadly 737 Max jets no longer a Boeing concern – for now: Production suspended after biz runs out of parking space

Anonymous Coward
Anonymous Coward

Re: Alternate 737MAX design kludge

The issues with low-slung engines are well known and designed for, with regard to pitch up with increasing power; the center of thrust isn't particularly far off from the previous models. However, a (rough) cylinder can become a significant lifting body when angle of attack increases, and the larger, further forward engine nacelles do just that. If you're flying at low speed and high angle of attack, it's possible that they'll generate enough lift to counteract your horizontal stabilizer's lift, making the aircraft very easy to pitch up. Requiring progressively less, and possibly after a certain point, no additional control column pressure to increase a given control input violates requirements that control feedback resist this, and leaves the aircraft uncertifiable without something like MCAS to prevent this tendency. You can think of MCAS as a system to counter-balance the engine nacelle lift, to allow it to handle as the previous model did with smaller engines (not necessarily designed as an anti-stall system, but it does prevent certain flight conditions that could rapidly lead to a stall).

(others already commented about the nature of the ducts, so i've removed that part of this comment)

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