Boeing has temporarily stopped making 737 Max airplanes • Hacker News Board

Re: Boeing has temporarily stopped making 737 Max airplanes

#121

Post by jaywalk » Tue, Jan 21, 2020, 8:48 PM UTC

Gibbon1 wrote: post #100

wang_li wrote: post #90

Earlier quoted context omitted.

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,…

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.

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.

Re: Boeing has temporarily stopped making 737 Max airplanes

#122

Post by Gibbon1 » Tue, Jan 21, 2020, 8:55 PM UTC

julienfr112 wrote: post #119

Gibbon1 wrote: post #100

Earlier quoted context omitted.

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.

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

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.

Re: Boeing has temporarily stopped making 737 Max airplanes

#123

Post by ajross » Tue, Jan 21, 2020, 9:00 PM UTC

madengr wrote: post #57

mrtksn wrote: post #34

Earlier quoted context omitted.

Would restarting Chernobyl make it the safest NPP considering the amount of scrutiny that it would be put through? Maybe we should look into re-introducing Windows Vista, considering the scrutiny that it would require it must be the safest and most stable OS ever.

No, that reactor had an inherent instability that could not be fixed. The MCAS has an issue with redundant AOA sensors; that specifically needs to be fixed. The MCAS caused problems on other flights, but the pilots knew to disable it by flipping the circuit breaker. The pilots on the crashed planes did not know to disable it. That is a training issue. Fix the redundant AOA and provide training to disable the MCAS, an…

The positive void coefficient problem[1] was intractable (without putting the whole reactor vessel inside a pressurized tank), but it was the combination of that and the control rod design that caused the explosion. The control rods were modified trivially. The reactor is basically safe, though you wouldn't repeat the design choices.

[1] An IMHO stupidly obfuscated way of saying that the cooling water around the reactor was an unpressurized pool that would boil if it got hot. Low-density bubbles of steam absorb fewer neutrons than liquid water, so when it boils the core gets hotter, not cooler.

Re: Boeing has temporarily stopped making 737 Max airplanes

#124

Post by hhas01 » Tue, Jan 21, 2020, 9:07 PM UTC

wang_li wrote: post #90

hhas01 wrote: post #84

Earlier quoted context omitted.

MAX is Defective by Design. Leave the aerodynamically unstable designs for the hotshot fighter planes; everyone else just wants to get from A to B without cratering into the ground inbetween.

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,…

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.

Re: Boeing has temporarily stopped making 737 Max airplanes

#125

Post by cameldrv » Tue, Jan 21, 2020, 9:09 PM UTC

BitwiseFool wrote: post #2

According to the article Boeing has halted production, but this leaves the door open to producing them again in the future after design updates. I predict they'll try to rename the model and fly it again after making changes and certifying. That being said, I never want to fly on a 737 Max or whatever they plan to rebrand it as.

The 737NG is out of production, and Airbus currently has something like a 5 year backlog of A320 orders. The only other direct competitor is the Comac C919. Boeing has already made about 1000 737MAXes. The 737MAX is going to be a significant part of the global airline fleet whether you like it or not. There will be many routes where the 737MAX is the only aircraft flying that route.

I think it's fairly unlikely that there's some other massively dangerous failure mode of the 737MAX, because the fleet has flown enough hours, and the only crashes have been the result of the MCAS. When that's fixed, it's quite possible that there are other gremlins that cause crashes, but they probably will be much less severe/likely than the MCAS problem.

Re: Boeing has temporarily stopped making 737 Max airplanes

#126

Post by acqq » Tue, Jan 21, 2020, 9:11 PM UTC

zaroth wrote: post #36

EDIT: And an hour after writing this Boeing just now announcing (surprise, surprise) they don’t expect return-to-service until July and stock is currently trading down 5.5%) I shorted BA for a few months based on many HN posts after the crashes, but covered my position after it seemed to stabilize at ~320. I think it will probably head lower, but as a general rule I try to find companies I believe in rather than comp…

> Today they have as I understand it just ~750 total pilots and engineers on staff to review technical data from the plane manufacturers. The FAA said last year to do it themselves they would need 10,000 more. [5]

Not 10000 more pilots and engineers. 10000 more employees. Now they have "1,300 employees, 745 of whom are pilots, engineers and technical staff who oversee design approvals and production."

Re: Boeing has temporarily stopped making 737 Max airplanes

#127

Post by JaRail » Tue, Jan 21, 2020, 9:12 PM UTC

missosoup wrote: post #103

BitwiseFool wrote: post #2

According to the article Boeing has halted production, but this leaves the door open to producing them again in the future after design updates. I predict they'll try to rename the model and fly it again after making changes and certifying. That being said, I never want to fly on a 737 Max or whatever they plan to rebrand it as.

> That being said, I never want to fly on a 737 Max or whatever they plan to rebrand it as. Yeah you will. Good luck selectively avoiding the most popular international route plane. Historically, people have been very quick to forget mishaps with particular airframes and revert to flying the most convenient/economical routes. And by the time it's flying again, it will be hands down the safest plane that's being opera…

You can check it all you want. That won't change the physics of its dynamically unstable design.

Re: Boeing has temporarily stopped making 737 Max airplanes

#128

Post by peeters » Tue, Jan 21, 2020, 9:12 PM UTC

IfOnlyYouKnew wrote: post #114

caycep wrote: post #73

One question in my mind is: what would it take for the old "engineer" faction of Boeing to come to the top again? Or is this unrealistic as the "management/costcutting" faction is just inherently better a "management" politics to ever be dislodged? Failing this, what is the likelihood a competitor with old-school Boeing values might emerge to compete, in such a capital-heavy industry?

This MBA vs engineering dichotomy is a myth. One of the people with a lot of responsibility for this disaster is the Chief Test Pilot, who is a Navy Veteran, engineer and prototypical flight enthusiast. That didn't stop him from lying to the FAA. Airplane travel today is also about 70x safer than it was in, say, the 1960s, on a per-passenger-per-mile basis. Despite Boeing's trouble, plane construction, pilot instruct…

Wasn't the ex-CEO also a Boeing engineering lifer?

Re: Boeing has temporarily stopped making 737 Max airplanes

#129

Post by internet_user » Tue, Jan 21, 2020, 9:21 PM UTC

totalZero wrote: post #91

caycep wrote: post #73

One question in my mind is: what would it take for the old "engineer" faction of Boeing to come to the top again? Or is this unrealistic as the "management/costcutting" faction is just inherently better a "management" politics to ever be dislodged? Failing this, what is the likelihood a competitor with old-school Boeing values might emerge to compete, in such a capital-heavy industry?

It's basically impossible for a competitor with "old school" values to emerge. The regulatory hurdles and foreign competition are daunting. There are only two companies in the world that can do what Airbus and Boeing do.

What are the two other companies? Lockheed and Tupolev?

Re: Boeing has temporarily stopped making 737 Max airplanes

#130

Post by hhas01 » Tue, Jan 21, 2020, 9:22 PM UTC

Gibbon1 wrote: post #122

julienfr112 wrote: post #119

Earlier quoted context omitted.

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

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.

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...