3 ms·

> Your job isn't in this area I guess. I'm sure of it. I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well unde

> Your job isn't in this area I guess. I'm sure of it. I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. I can't even begin to imagine the multiphysics that goes into simulating a nuclear weapon, but if we are willing to bet our entire nuclear deterrent on it, it seems reasonable to skip some additional rounds of physical tests that are mostly a formality at this point. Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. And then you apply a factor of safety on your calculations for added assurance.

samcday 7y ago
> Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. Okay so maybe this is an apple's to oranges comparison, but I thought of the story how NASA was scammed by a supplier passing off shitty aluminium as space grade [1]. Is it reasonable to assume that if it can happen to NASA, it can happen to Boeing? https://weather.com/news/news/2019-05-02-nasa-launch-failures-caused-by-faulty-aluminum-scam https://weather.com/news/news/2019-05-02-nasa-launch-failure...
- chroem- 7y ago
  They check the airframes with nondestructive ultrasonic testing that doesn't involve oblitering entire aircraft. That would be caught at one of several different QA points. We're mostly talking about design verification, which is different.
  - tempguy9999 7y ago
    Parent post gave the example I was remembering. And the company, Sapa, didn't (AFAICT) manufacture the components, they were a third-party testing service! They provided exactly the tests you say should have picked up the problems.
kanaba 7y ago
> I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. I am not a mechanical engineer. My understanding is that some composite materials used in modern aircraft manufacturing can fail in ways unlike classic aircraft aluminum (i.e. suddenly, without prior visible signs of stress/wear). Is that relevant here?
- goatinaboat 7y ago
  I am a mechanical engineer, and yes it is. The composites are simply too new to have all their properties adequately modelled yet. And they are a moving target.
salawat 7y ago
>I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. And we still get it wrong at times; especially with interactions between disparate parts. See the fatigue problems caused as a result of interactions between the engines and fuselage of the C-133 Cargomaster, or how the F/A-18 had a habit of destroying it's vertical stabilizer due to generated turbulence unaccounted for in the original design. All the FEA in the world gives you a good estimate when you abstract away the details. It doesn't give you the 'real story'. > I can't even begin to imagine the multiphysics that goes into simulating a nuclear weapon, but if we are willing to bet our entire nuclear deterrent on it, it seems reasonable to skip some additional rounds of physical tests that are mostly a formality at this point. This is a false equivalence. Nuclear weapons testing has been strictly limited by international accord. You cannot physically test these weapons anymore without "waking up the neighbors" and leading to exceedingly difficult to defuse international scrutiny. That's why the copious levels of "in theory" with regard to nuclear weapons is a reasonable route to take. There is literally no other way to advance the state of the Art. Planes thankfully, don't have that issue. Also, while nuclear weapons testing wasn't restricted, test destinations were done with some degree of regularity; so again, the nuclear weapon point fails. >Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. And then you apply a factor of safety on your calculations for added assurance. Just like those leading edge slats for 737 NG, MAX 8 right? You know, the ones that lead to a grounding of aircraft that had already been carrying passengers recently? And who is doing that quality assurance? That bunch of "Quality" people Boeing laid off/relocated elsewhere a few months ago? Not a credentialed engineer, but know more than enough to LARP as one in certain fields. Testing, aviation/aerodynamics, mechanics of materials, and software being some of them. You simply cannot know what you're dealing with until you actually test it, and it's generally right after you stop doing that one test that just tells you exactly what you think it should that you get that design with a problem that would have manifested if you just did it. The only people who should be interested in decreasing testing is the sales, accounting, and business departments. As Engineers, we've had upward of 100 years of design driven 'oopsie' to grind into us the fact we are, in fact, not as clever at accounting for the real world as we think we are. The fact that as a credentialed mechanical engineer, you don't see it this way is concerning. Though again, I've not had my scrutinous edges rounded off by regular business constrained application either. So there is that.
deleted 7y ago
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samcday 7y ago

> Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. Okay so maybe this is an apple's to oranges comparison, but I thought of the story how NASA was scammed by a supplier passing off shitty aluminium as space grade [1]. Is it reasonable to assume that if it can happen to NASA, it can happen to Boeing? https://weather.com/news/news/2019-05-02-nasa-launch-failures-caused-by-faulty-aluminum-scam https://weather.com/news/news/2019-05-02-nasa-launch-failure...

chroem- 7y ago
They check the airframes with nondestructive ultrasonic testing that doesn't involve oblitering entire aircraft. That would be caught at one of several different QA points. We're mostly talking about design verification, which is different.
- tempguy9999 7y ago
  Parent post gave the example I was remembering. And the company, Sapa, didn't (AFAICT) manufacture the components, they were a third-party testing service! They provided exactly the tests you say should have picked up the problems.

kanaba 7y ago

> I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. I am not a mechanical engineer. My understanding is that some composite materials used in modern aircraft manufacturing can fail in ways unlike classic aircraft aluminum (i.e. suddenly, without prior visible signs of stress/wear). Is that relevant here?

goatinaboat 7y ago
I am a mechanical engineer, and yes it is. The composites are simply too new to have all their properties adequately modelled yet. And they are a moving target.

salawat 7y ago

>I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. And we still get it wrong at times; especially with interactions between disparate parts. See the fatigue problems caused as a result of interactions between the engines and fuselage of the C-133 Cargomaster, or how the F/A-18 had a habit of destroying it's vertical stabilizer due to generated turbulence unaccounted for in the original design. All the FEA in the world gives you a good estimate when you abstract away the details. It doesn't give you the 'real story'. > I can't even begin to imagine the multiphysics that goes into simulating a nuclear weapon, but if we are willing to bet our entire nuclear deterrent on it, it seems reasonable to skip some additional rounds of physical tests that are mostly a formality at this point. This is a false equivalence. Nuclear weapons testing has been strictly limited by international accord. You cannot physically test these weapons anymore without "waking up the neighbors" and leading to exceedingly difficult to defuse international scrutiny. That's why the copious levels of "in theory" with regard to nuclear weapons is a reasonable route to take. There is literally no other way to advance the state of the Art. Planes thankfully, don't have that issue. Also, while nuclear weapons testing wasn't restricted, test destinations were done with some degree of regularity; so again, the nuclear weapon point fails. >Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. And then you apply a factor of safety on your calculations for added assurance. Just like those leading edge slats for 737 NG, MAX 8 right? You know, the ones that lead to a grounding of aircraft that had already been carrying passengers recently? And who is doing that quality assurance? That bunch of "Quality" people Boeing laid off/relocated elsewhere a few months ago? Not a credentialed engineer, but know more than enough to LARP as one in certain fields. Testing, aviation/aerodynamics, mechanics of materials, and software being some of them. You simply cannot know what you're dealing with until you actually test it, and it's generally right after you stop doing that one test that just tells you exactly what you think it should that you get that design with a problem that would have manifested if you just did it. The only people who should be interested in decreasing testing is the sales, accounting, and business departments. As Engineers, we've had upward of 100 years of design driven 'oopsie' to grind into us the fact we are, in fact, not as clever at accounting for the real world as we think we are. The fact that as a credentialed mechanical engineer, you don't see it this way is concerning. Though again, I've not had my scrutinous edges rounded off by regular business constrained application either. So there is that.

deleted 7y ago

[deleted]