Canada bans Boeing's 737 MAX; U.S. now the last major country where it can fly


#1

Originally published at: https://boingboing.net/2019/03/13/canada-bans-boeings-737-max.html


#2

@Akimbo_NOT - I owe you a coke.


#3

Probably nothing fundamentally wrong with the plane. What is wrong is expecting software to ensure the safety of human beings.

Of course the US will be the last to call this out, because Boeing is a US company. Now let’s address the root cause.


#4

“Deathliner” is like “death” and “airliner”. Funny and grim at the same time!


#5

They apparently strapped far too large/heavy engines to the airframe. Without anywhere near enough re-engineering of the airframe to make it fly well. This makes it prone to listing backwards, nose up, in flight. Because its got way more weight hanging off the back than it was ever designed for. Pilots have apparently been complaining about its flying characteristics since before it was available.

The software everyone keeps talking about is basically an autopilot feature designed to compensate for that. Plane tilts back and the software basically steers towards to ground to level it out. That’s a bad idea, and there’s absolutely something wrong with the plane.

The company scrapped a plan to develop a replacement for the 737, a design from 1968. When Airobus announced a new version of the A320 with more efficient engines, and airlines started buying. Boeing basically just bolted new engines that were far too heavy onto an airframe they knew needed to be replaced to have something to compete. Because it was cheaper and faster than following through on the initial idea of developing a new plane. The software was duct tape on a plane they knew was fucked aeronauticly.


#6

737 engines are on the wings


#7

Yeah but usually sit behind the center of gravity, or on this model otherwise torque the wings down towards the back.


#8

“The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system. Airframe design is a field of aerospace engineering that combines aerodynamics, materials technology and manufacturing methods to achieve balances of performance, reliability and cost.”
– Michael C. Y. Niu (1988). Airframe Structural Design . Conmilit Press LTD


#9

Really - I’ve not heard that before about this 737. Can you refer me to an article that discusses the issue where by the mass of the engines required software adjustments to control systems?


#10

I was not suggesting that the wings were not part of the airframe as your quote implies. I was pointing out that the engines are not at the “back” of the plane as implied by the OP, but rather pylon mounted below the wings - generally towards the center of the airframe.

But thanks for caring enough to post that.


#11

I’ll see if I can track one down. News radio station I keep on during work has had pilots and aviation engineers and what have on explaining it nearly every time the story comes up in rotation.


#12

That is your interpretation of the OP.


#13

#14

Thanks for the link. The article does mention that a tendency to pitch up was introduced with the new engines, and the control systems were altered to counter this.

While this sounds odd, the ability for a control system to overcome a designed instability is not new technology. I believe this was first vetted in the X29 experimental plane (forward swept wing format) which was inherently unstable, but was made flyable by the control system which could react fast enough to overcome it tendency to move from the desired direction. Interesting reading if your curious about this stuff. Darpa article, Wikipedia.

But returning to the original question - the article says nothing about the engines being more rearward, or their additional weight making the plane tail heavy. It does however state the engines were a larger diameter. From this we can understand it would require them to be hung with the center line lower than the original engines, and it would also mean that the thrust vector of the engines would be further away from the engines centerline, and further below the planes center of gravity. If you have a basic understanding of physics you realize this means the new engines introduced a higher rotational vector around the plane’s center of gravity - longer lever, more force - and this rotation would tend to make the nose rise.

But I think the control system could be designed to overcome this. I think what will be revealed is that the UI for the system that manages this was poorly designed, and/or crews were poorly trained on how to interact with it. This is going to be an error in human factors more than the design of the airframe or placement of the engines.


#15

The aircraft where you hear about that sort of thing are military in nature, usually having some sort of specialized use that makes the instability worth dealing with along with limited flight times and intense maintenance schedules that mitigate the issue. Most of the famous ones have either been replaced by or lead to descendants with better flight characteristics.

And your own example is an experimental aircraft, designed in part to test the theory that such instability lead to better maneuverability. That didn’t turn out to be true, the plane never entered production. And the closest thing it had to direct descendants are all UAVs. As are almost all modern X Planes, cause that shits dangerous.

It’s also around 20 years more modern than the base 737 design.

It’s a very, very, very different situation from a civilian airliner designed to make multiple long distance flights, with 100’s of people on board, a day. For decades. And whether I misheard the exact details or not. The plane has a design problem. And that design problem is already likely to be responsible for at least 1 serious crash.

Civilian aircraft don’t get designed instability, nor do they have mission parameters that make a certain amount of loss justifiable.


closed #16

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