Heads should roll at Boeing

[Savs]

It seems to me, though, he contradicts himself in the space of a few days, and I wonder why.

I guess I'm not seeing the contradiction. Can you point it out to me?

Okay, but let's agree that these may not be verbatim.

Because the engines are further forward, the lift tends to push the nose up -- causing the angle of attack to increase further. This reinforces itself and results in a pitch-up tendency which if not corrected can result in a stall. This is called an unstable or divergent condition. It should be noted that many high performance aircraft have this tendency but it is not acceptable in transport category aircraft

and

There is not a fundamental problem in the design of the aircraft.

[Savs]

omanphil, you've been quiet. What hath you wrought?

[mettkeks]

I dunno about this RWD speak.

With the steering and force application separated, it sometimes comes in handy in avoiding peril. For instance, a trained driver can induce oversteer and as a result change the vehicle trajectory while maintaining velocity as needed. With FWD or AWD, understeer is the norm. While this is typically safer, it is not a given. Also, RWD usually favors a more neutral weight distribution which results in a better central moment for cornering and braking.

FWD wasn’t created for safety. It was created because it’s cheaper for vehicle assembly (the entire drivetrain installs into the chassis at once) and it has lower drivetrain losses (less inertia) and thus better fuel economy.

Drivetrain choice relies heavily on application. I don’t think it applies well to this airplane design problem.

Main disadvantage of AWD: "Hochdynamischer Grenzbereich": The limit changes from situation to situation. The grip while accelerating gives the illusion of safety, while this advantage disappears when decelerating/turning. "AWD will get you in trouble faster."

In the 5 years I'm driving, I never once got stuck with my FWDs, and there's a climb of 19% over 1km on my way to work (I live in a mountain region). In fact, my light 2600lb compact drives circles around those heavy limousines and SUV's in snow, up and especially down the mountain. AWD becomes more of a necessity than an advantage if your car is 5000lb+.

AWD with summer tires in winter is not going to work at all. No matter what you drive, get good winter tires.

[mgil]

This is a good article, (poison the well) including some interesting quotes from an MIT professor of aeronautics (appeal to authority):

https://www.forbes.com/sites/petercohan ... a202da40aa

Wonder why he changed his tune five days later. Hmmm. I see his funding comes from the FAA. I'm not saying there is funny business, but there sure could be.

That's an excellent point. In light of that, I guess he doesn't seem very credible, especially compared to the guy who claims to have written the first social media platform back in 1977 and recently flew a 757 in a flight sim.

I don't know the guy. It's quite possible he has a sterling reputation for credibility. It seems to me, though, he contradicts himself in the space of a few days, and I wonder why.

It's also true that I don't trust many engineers in academia, and I'm very sorry if that offends some people. I have worked closely with many engineering professors, have been coauthors on some of their papers, and there are quite a few I greatly admire. However, it is a little different than pure science, and that's all I'm going to say.

I don’t trust engineers either.

[Les]

This is called an unstable or divergent condition. It should be noted that many high performance aircraft have this tendency but it is not acceptable in transport category aircraft [emphasis mine] where there is a requirement that the aircraft is stable and returns to a steady condition if no forces are applied to the controls.

That's some fucking nuance.

So organic-agent manipulating actuators = bad?

Controller system manipulating actuators = a'ight?

EDIT: I'm assuming this is requirement in the US Code? If someone is familiar with the actual code, can you post? Really curious.

https://www.ecfr.gov/cgi-bin/text-idx?S ... 5&rgn=div5 Part 25 gives the airworthiness standards for Transport Category. I wasn't familiar with the rule that it has to be aerodynamically stable, but I've never looked at it that closely. For instance, there are other categories like normal, utility, etc. that have to meet certain G load standards among other things, but it doesn't matter if the aircraft is inherently stable or unstable.

Starts at 25.171- the plane needs to demonstrate stability under these parts, but it can probably do it with the help of fly by wire and still be legal.

A Cessna 172 is certified in both the Normal and Utility categories. When running in the utility category, it is then approved for things like spins. But it is a stable airplane. It's kind of cool showing it to a student. If you pull up on the yoke hard and let go, it will pitch up and down, but each oscillation will become more stable and eventually it will get back to normal flight. An unstable airplane does the opposite, with each oscillation getting worse. You would have to add control inputs or things could get bad. But I've seen both stable and unstable planes in these other categories. I'll have to look into it more.

[Cellist]

It seems to me, though, he contradicts himself in the space of a few days, and I wonder why.

I guess I'm not seeing the contradiction. Can you point it out to me?

Okay, but let's agree that these may not be verbatim.

Because the engines are further forward, the lift tends to push the nose up -- causing the angle of attack to increase further. This reinforces itself and results in a pitch-up tendency which if not corrected can result in a stall. This is called an unstable or divergent condition. It should be noted that many high performance aircraft have this tendency but it is not acceptable in transport category aircraft

and

There is not a fundamental problem in the design of the aircraft.

Since the A320 was designed to be fly-by-wire from the beginning, I think we can assume it’s aerodynamic stability is fundamentally worse, but acceptable.

-not from MIT

[Les]

Just to add...

Neutral point

A mathematical analysis of the longitudinal static stability of a complete aircraft (including horizontal stabilizer) yields the position of center of gravity at which stability is neutral. This position is called the neutral point. (The larger the area of the horizontal stabilizer, and the greater the moment arm of the horizontal stabilizer about the aerodynamic center, the further aft is the neutral point.)

The static center of gravity margin (c.g. margin) or static margin is the distance between the center of gravity (or mass) and the neutral point. It is usually quoted as a percentage of the Mean Aerodynamic Chord. The center of gravity must lie ahead of the neutral point for positive stability (positive static margin). If the center of gravity is behind the neutral point, the aircraft is longitudinally unstable (the static margin is negative), and active inputs to the control surfaces are required to maintain stable flight.

[Les]

It seems to me, though, he contradicts himself in the space of a few days, and I wonder why.

I guess I'm not seeing the contradiction. Can you point it out to me?

Okay, but let's agree that these may not be verbatim.

Because the engines are further forward, the lift tends to push the nose up -- causing the angle of attack to increase further. This reinforces itself and results in a pitch-up tendency which if not corrected can result in a stall. This is called an unstable or divergent condition. It should be noted that many high performance aircraft have this tendency but it is not acceptable in transport category aircraft

and

There is not a fundamental problem in the design of the aircraft.

Since the A320 was designed to be fly-by-wire from the beginning, I think we can assume it’s aerodynamic stability is fundamentally worse, but acceptable.

-not from MIT

I'm pretty sure that is correct. I think you can be certificated in the transport category with both something that is aerodynamically stable/unstable. Again, I might be wrong, but I'm pretty sure that is the case.

[Savs]

Since the A320 was designed to be fly-by-wire from the beginning, I think we can assume it’s aerodynamic stability is fundamentally worse, but acceptable.

-not from MIT

Now you have me googling like mad. I'm going to be an aviation expert before this day is done. Look out, Les!

That's just a joke, and not a very funny one, I suppose.

Can we assume that the A320's fly-by-wire relaxed the stability requirement? That's what I tried to find out. I'm going to quit now, because I don't want to be an expert beginner, and it would be charitable to say I've even begun.

Not even sure if applicable, but I found this:

A-320 (to be precise, A-318) and the later versions produced by that company have only fly-by-wire controls. However, none of them have utilised the relaxed stability concept so far.

https://www.quora.com/Aviation-When-the ... e-aircraft

[omaniphil]

omanphil, you've been quiet. What hath you wrought?

Sorry, I've been on vacation, but have been diligently following this thread whilst toting toddlers in and around the alleys of old Prague.

This has been a really fascinating discussion, and I feel like I've learned a lot. Thanks in particular to Les who has brought some really interesting perspectives to bear on this.

I'm probably mostly in the Root and Hanley camp of not wanting to add further complexity to a imperfect design, but appreciate Matt's view on this just being another scenario where a control system should be able to take care of imperfect inputs to create a better output.

With regard to some of the discussion about this being a fault of capitalism, and the desire to just make money, I'm a little bit more skeptical of that aspect. I'm probably more apt to attribute this to a problem with crony capitalism and more specifically to regulatory capture.

My solution would be to limit the regulatory scope of government to avoid capture in the first place. But then I guess I'm just a libertarian who is a broken record on these things...

[cwd]

My solution would be to limit the regulatory scope of government to avoid capture in the first place. But then I guess I'm just a libertarian who is a broken record on these things...

I suspect that even on Coconut Island, the private Consumer-Reports type certifying company would also suffer from regulatory capture.

The only difference is that when the private regulatory company screws up, it goes bankrupt and is overtaken by a competitor, rather than being reorganized by Congress. Either way, the successor agency/company will be forced to re-hire most of the staff of the old organization.

I'm less and less sure that the big political divides matter all that much. Tech/science progress, and cultural stuff (corruption levels) matter a lot. Russia didn't get all that much better when communism ended.

[Mattjd]

woah woah woah

You said Coconut Island.

Is omaniphil mikelikey??

[BigE]

Today old man radio (NPR) had a good piece on the lack of quality control and whistle blower retaliation at Boeing.

[DoctorWho]

woah woah woah

You said Coconut Island.

Is omaniphil mikelikey??

Conspiracy theory:
Mikey hasn't been around for a while, long enough for him to go to law school where exposure to new ideas weakens, but doesn't kill, his understanding of the role of the free market and the role of government. He goes in thinking a law degree would help his (accounting? auditing? CPA? finance?) career but instead finds patent law.

Mikey emerges as a libertarian Omaniphil (both from Ohio?), but now private ordering is no longer the solution to every problem.

[Allentown]

woah woah woah

You said Coconut Island.

Is omaniphil mikelikey??

Conspiracy theory:
Mikey hasn't been around for a while, long enough for him to go to law school where exposure to new ideas weakens, but doesn't kill, his understanding of the role of the free market and the role of government. He goes in thinking a law degree would help his (accounting? auditing? CPA? finance?) career but instead finds patent law.

Mikey emerges as a libertarian Omaniphil (both from Ohio?), but now private ordering is no longer the solution to every problem.

I've never seen them both in the same room, so this checks out.

[cwd]

You said Coconut Island.
Is omaniphil mikelikey??

Conspiracy theory:
Mikey hasn't been around for a while, long enough for him to go to law school where exposure to new ideas weakens, but doesn't kill, his understanding of the role of the free market and the role of government. He goes in thinking a law degree would help his (accounting? auditing? CPA? finance?) career but instead finds patent law.

Mikey emerges as a libertarian Omaniphil (both from Ohio?), but now private ordering is no longer the solution to every problem.

I've never seen them both in the same room, so this checks out.

Actually, Mikey and DoctorWho are both my sock puppets.

Mikey is my uber-Libertarian POV, DoctorWho is my golf-course Republican POV, leaving me to be the blue-collar intellectual moderate voice of reason.

It all leads up to a presidential run in 2024, as a less-insane populist Republican.

DirtyRed is an experiment to see what it takes to pick up some of the pro-wrestling-fan voters.

There are only about 4-5 people on this forum in reality.

[Les]

Since the A320 was designed to be fly-by-wire from the beginning, I think we can assume it’s aerodynamic stability is fundamentally worse, but acceptable.

-not from MIT

Now you have me googling like mad. I'm going to be an aviation expert before this day is done. Look out, Les!

That's just a joke, and not a very funny one, I suppose.

Can we assume that the A320's fly-by-wire relaxed the stability requirement? That's what I tried to find out. I'm going to quit now, because I don't want to be an expert beginner, and it would be charitable to say I've even begun.

Not even sure if applicable, but I found this:

A-320 (to be precise, A-318) and the later versions produced by that company have only fly-by-wire controls. However, none of them have utilised the relaxed stability concept so far.

https://www.quora.com/Aviation-When-the ... e-aircraft

Yes, some airplanes are fly by wire not for instability, but for flight envelope control. Again, this comes down to the sometimes shoddy pilot skills in the developing countries. For instance, Captain Ho spun a 747! I don't think the A320 could ever get into that situation without the computer taking over.

[DoctorWho]

You said Coconut Island.
Is omaniphil mikelikey??

Conspiracy theory:
Mikey hasn't been around for a while, long enough for him to go to law school where exposure to new ideas weakens, but doesn't kill, his understanding of the role of the free market and the role of government. He goes in thinking a law degree would help his (accounting? auditing? CPA? finance?) career but instead finds patent law.

Mikey emerges as a libertarian Omaniphil (both from Ohio?), but now private ordering is no longer the solution to every problem.

I've never seen them both in the same room, so this checks out.

Actually, Mikey and DoctorWho are both my sock puppets.

Mikey is my uber-Libertarian POV, DoctorWho is my golf-course Republican POV, leaving me to be the blue-collar intellectual moderate voice of reason.

It all leads up to a presidential run in 2024, as a less-insane populist Republican.

DirtyRed is an experiment to see what it takes to pick up some of the pro-wrestling-fan voters.

There are only about 4-5 people on this forum in reality.

Fake news (at least that's what I'm going to tell the people at the Democratic fund-raiser I'm trying to arrange). The only question is whether this slight mistake was intentional to discredit the theory. Per Allent, all the pieces fit together.

[JonA]

Yes, some airplanes are fly by wire not for instability, but for flight envelope control.

We digressed quite a bit into stability/fundamental design a bit, but from what I read, the MCAS software that failed wasn't generally active to make the plane stable, it just activated if the plane got into an unsafe stall conditions. (Or if a sensor malfunctioned. )

[damufunman]

Yes, some airplanes are fly by wire not for instability, but for flight envelope control.

We digressed quite a bit into stability/fundamental design a bit, but from what I read, the MCAS software that failed wasn't generally active to make the plane stable, it just activated if the plane got into an unsafe stall conditions. (Or if a sensor malfunctioned. )

One issue with the new plane was that going into a stall condition made it unstable due to the nacelle now contributing to lift (and pitch up due to the center of pressure being ahead of the CG, presumably), and subsequently increasing AoA at high AoA (if i receall correctly), which is an unstable condition.

- not an aeronautical engineer