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Comment by sangnoir | Hacker News Reader

It's not the center of gravity that causes pitch-up - it's additional lift by engine nacelles at higher angles of attack; this lift increases the AoA further due to the position of the engines relative to the wing. This feedback loop leads to a stall when the angle gets high enough

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Probably not completely true. An airfoil stalls when the critical angle of attack is exceeded. For most airfoils, this sits at around 17°. For all commercial aircrafts (I think 727 onwards) there is a mechanism called stick pusher that will not allow an airfoil to go over critical AoA. I am not sure if this has been overridden somwhere in the 737 Max 8 though.

Are you saying 17deg from horizontal? Let's ignore wind and other influences. A normal plane can not climb more steeply than 17deg?

I'm not implying you're wrong, just very surprised to see this low a number. I would have guessed much closer to something like 45deg, maybe even more.

The Angle of Attack is defined as the angle between relative wind and chord of an airfoil. So if your engine has enough juice to climb at 45° (and many aerobatic aircrafts do), your relative wind is coming at 45° from ground, but almost at 0° with respect to the chord. So your wing is still flying.

Let me know if that makes sense.

I was describing the physical "bug" Boeing was solving in software: MCAS is a stick-pusher because it forces down the nose - which led to the Lion air crash because of a faulty AoA sensor made MCAS avoid an imaginary stall, forcing the nose down into a powered flight into terrain.

They should have put spoilers on the nacelles instead of trying to fix the planes bad aerodynamics in software.

Yeah you would know.

How do you know that I don't know.

Please explain.

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