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The most expensive number in engineering

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Re: The most expensive number in engineering

#151

Post by krapp »

nearbuy wrote: post #150
dragontamer wrote: post #85

Earlier quoted context omitted.

And Vulcan are space elves, Klingon are space orcs and Borg are space undead. All of this stuff has inspiration from classical fantasy. That doesn't change whether or not something is SciFi or not. There is an intersection of SciFi and Fantasy for sure, and the line gets blurred. Artificial human stories can be cyborgs, androids, clones, golems, or chimera, or even explicit fantasy races like minotaurs. If it's an an…

I see the similarities for Klingons and Borg, but I don't see much similarity between Vulcans and elves beyond the pointy ears. Vulcans are more like androids: logical and outwardly emotionless, but not necessarily wise. The human captain (e.g. Kirk) tends to figure out a winning solution despite the resident Vulcan often complaining it isn't logical. That doesn't detract from your point.

IIRC, Spock's appearance was intended to look vaguely demonic or Satanic, rather than like an elf. The original concept had him with red skin and deeply arched eyebrows as well, but they had to tone the makeup down a lot to avoid offending religious viewers.

Re: The most expensive number in engineering

#152

Post by krapp »

gourlaysama wrote: post #62
ben_w wrote: post #58

Earlier quoted context omitted.

> For the record, Star Wars is not science fiction nor has it ever been portrayed as such. FWIW this is literally the first time I’ve encountered someone claiming that it isn’t science fiction. ( Soft SciFi, to be sure, but still: https://tvtropes.org/pmwiki/pmwiki.php/Main/MohsScaleOfScien... )

> FWIW this is literally the first time I’ve encountered someone claiming that it isn’t science fiction. Well, there's Science Fantasy [1]: Jedi and the Force are very much Wizards and Magic. I've heard it called Space Fantasy, too. [1]: https://tvtropes.org/pmwiki/pmwiki.php/Main/ScienceFantasy

>Jedi and the Force are very much Wizards and Magic

Star Trek canonically has telepaths, telekinesis, and godlike beings that can alter reality with mere thought.

Why don't people call Star Trek space fantasy as well, when its universe is even less grounded in realism than Star Wars?

Re: The most expensive number in engineering

#153

Post by saalweachter »

lamontcg wrote: post #57
codeflo wrote: post #35

The article suggests using a probabilistic failure model instead of a large a safety factor, and explains how a safety factor established in the 1930s affected the cost of the Space Shuttle. But spacecraft might be a special case, where any additional weight is so expensive, and you also expect the models to be especially accurate and manufacturing to be extremely precise. For more everyday civil engineering, I think…

Or more simply: planes that get hit with massive unexpected turbulence shouldn't just drop out of the sky and kill everyone on board. And to paraphrase the great philosopher Donald Rumsfeld, it is all about the unknown-unknowns.

Any plane that can land missing half a wing on one engine is over-engineered, from a certain point of view.

Re: The most expensive number in engineering

#154

Post by joshjdr »

supermatt wrote: post #148

Any idea where I can learn some simple structural engineering? For example, I want to build a small building. I want to be able to calculate things like the snow load of the roof, make a suitable truss, take into consideration things like the safety factor, and build with the materials to meet those requirements. I can buy plans for similar constructions, but i don't see how they decide what size wood to use where, e…

You may want to try reading your local building code. This may not get into engineering principles at the level you’re seeking, but it may effectively provide the functional understanding of how (if not why) a certain material/size has been specified in its application- esp. if you’re working from (or modifying) similar plans.

Re: The most expensive number in engineering

#155

Post by mannykannot »

whatshisface wrote: post #19
supernova87a wrote: post #16

If you had the luxury of throwing away bridges or planes or space shuttles to test every possible circumstance, then I guess eventually the safety factor could conceivably come down to 1.0, right? You would've satisfied yourself that nothing in the real world was not in your simulations?

A safety factor of 1.5x does not guarantee that nature will not throw 1.6x the expected force at you. That's why the author of the article calls it a "libation," because it isn't related to anyone's knowledge about the uncertainties in the situation at hand.

The author's point of view here is somewhat undermined by his own article, in which he points out that the figure has been adjusted downwards over time in response to experience - in other words, it has been empirically determined. It might not be the most efficient or flexible way to handle risk, but it is not just a faith-based number, either.

Re: The most expensive number in engineering

#157

Post by mannykannot »

afterburner wrote: post #84
londons_explore wrote: post #71

The real number engineers should be considering is not the factor of safety, but the probability of failure. The probably of failure should be calculated considering material defects, forces larger than predicted, simulation errors, and all other causes the factor of safety is designed to protect against. Then the engineering process can allocate those probabilities in the most efficient way. For example, in a rocket…

Unfortunately, NASA was really bad at estimating the probability of failure. Feynman famously dissed their lack of mathematical rigour in this regard. I'm guessing most engineers' grasp of proper statistics math is worse than their understanding of factors of safety.

Indeed, though my recollection of Feynman's most pertinent criticism is that he suspected that the probability of failure of the thousands of individual components - probabilities that are all very small numbers - were picked with one eye on how they moved the overall risk. He felt that the analysis, which should have been bottom-up (and nominally was) was actually conducted in a top-down manner.

The space shuttle program demonstrated that if your analysis overlooks just one scenario (such as a rigid O-ring or ice on the bipod ramp), the risks can be much greater than you calculate.

Re: The most expensive number in engineering

#158

Post by ineedasername »

How is it possible that this number that costs billions of dollars doesn’t have a clear and universally accepted definition

Because design constraints are not universal across all projects. Human error for something like the space shuttle is fairly minimal considering the mind boggling amount of training that's done. If you have an unreliable or unproven materials provider then that present a design constraint that must be accounted for. Etc.

Re: The most expensive number in engineering

#159

Post by benhurmarcel »

lamontcg wrote: post #57
codeflo wrote: post #35

The article suggests using a probabilistic failure model instead of a large a safety factor, and explains how a safety factor established in the 1930s affected the cost of the Space Shuttle. But spacecraft might be a special case, where any additional weight is so expensive, and you also expect the models to be especially accurate and manufacturing to be extremely precise. For more everyday civil engineering, I think…

Or more simply: planes that get hit with massive unexpected turbulence shouldn't just drop out of the sky and kill everyone on board. And to paraphrase the great philosopher Donald Rumsfeld, it is all about the unknown-unknowns.

Massive turbulence is taken into account in the loads calculation (JAR 25.341). It's not supposed to be in the safety factor.
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