Boeing has temporarily stopped making 737 Max airplanes

Re:Boeing has temporarily stopped making 737 Max airplanes by wang_li on Tuesday January 21, 2020 @02:57PM (#22110842)

Is it unstable? I thought the problem was that they didn't want to require retraining so they built in a flight control system that made it seem like the previous generation plane from a flight dynamics pov. That system would only take inputs from a single sensor on any given flight. If that sensor had issues then the flight control system would misbehave. If they had gone the retraining route and not included MCAS, then the plane would be fine. At least that was my understanding.

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Re:Boeing has temporarily stopped making 737 Max airplanes by hhas01 on Tuesday January 21, 2020 @04:07PM (#22111577)

I suspect they’d need to teach those pilots to add a lot of trim. Putting those big engines well ahead of the CoG makes them throw its nose up; it’s basic Newtonian levers.

Not that any plane flies perfectly level at all speeds, which is why they need trim in the first place. But presumably there’s a “sweet spot” which the original 737 was designed to nail in normal flight, which subsequent revisions have moved further and further away from.

At some point you really need an adult in the room to stand up and declare “no more”. But by accounts McDonnell-Douglas already showed all the grown-ups the door. That’s the nice thing about responsibility: just disseminate it enough, and no-one’s to blame.

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Re:Boeing has temporarily stopped making 737 Max airplanes by Gibbon1 on Tuesday January 21, 2020 @03:19PM (#22111066)

I think most aircraft are unstable or have quirks outside their approved flight envelope. For passenger aircraft you want it to be docile and predictable inside that. The MAX far as I've gleaned naturally wants to pitch up at high angles of attack. And that the problem is more severe than they expected when they initially designed the thing.

The MCAS might have been okay if the behavior matched initial expectations.

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Re:Boeing has temporarily stopped making 737 Max airplanes by julienfr112 on Tuesday January 21, 2020 @03:46PM (#22111355)

Are you sure ? I though it wanted to pitch up when engines where at full throttle, not because of angles of attack.

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Re:Boeing has temporarily stopped making 737 Max airplanes by Gibbon1 on Tuesday January 21, 2020 @03:55PM (#22111446)

I think what I've read is the engine nacelles create lift at higher angles of attack. Because the nacelles are larger and located more forward than in older models. That's the source of the extra lift. Might also be the engines also contribute.

On the other hand I'm just a bystander in all this.

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Re:Boeing has temporarily stopped making 737 Max airplanes by hhas01 on Tuesday January 21, 2020 @04:22PM (#22111738)

Also consider the position of the thrust point relative to the plane’s center of gravity. Being positioned below and ahead of the CoG, the engines naturally try to push the plane around it, i.e. nose-up.

Mind you, my physics ed stopped after high school (though even that much is enough to do a double-take at MAX). This looks like a much better explanation:

https://www.quora.com/Where-should-the-center-of-mass-lift-a...

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Re:Boeing has temporarily stopped making 737 Max airplanes by jaywalk on Tuesday January 21, 2020 @03:48PM (#22111384)

It pitches up with throttle, due to the position of the engines. Angle of attack sensors feed MCAS, so it can detect the pitching up and adjust the elevator trim to counteract it.

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