Door blows off Boeing 777X during stress test • Hacker News Board

Re: Door blows off Boeing 777X during stress test

#71

Post by inferiorhuman » Sat, Sep 07, 2019, 3:53 AM UTC

ajross wrote: post #62

cyberferret wrote: post #16

It's a stress test. You would expect things to break during a stress test. > "They loaded it up well beyond capacity and bent its wings in an extreme manner, in a way almost certain to never happen in the real world." Here is another video of a 777 wing test where it broke at 154% of the [s/normal/maximum theoretical/] load - a bit beyond what was expected by the engineering team. https://www.youtube.com/watch?v=Ai2H…

You expect things stressed beyond limits to break where you expect them to, and the point of the test is to show that the failure modes are the expected ones. Having a door pressure seal fail explosively during an airframe stress test sounds to me very much like an UNexpected failure mode. That's bad.

It's doubly unexpected as, in theory, the 777X is just a variant of the 777, itself a plane that didn't blow its doors out under testing.

Re: Door blows off Boeing 777X during stress test

#72

Post by tempestn » Sat, Sep 07, 2019, 3:57 AM UTC

ChuckMcM wrote: post #70

rtomanek wrote: post #67

Earlier quoted context omitted.

I would still expect the `maximum theoretical load` to be well above the `designed limit load`.

And it is, it is 154% or slightly more than 2.5x the 'design limit load'.

Slightly more than 1.5x you mean. And yeah, since the design limit load is already going to have a safety margin over the max anticipated load, as long as the test performs some amount beyond that design level, it's good.

Edit: This is assuming the 'design level' is the level it was designed to withstand, which is how I would normally understand the term. Having watched the full video now though, it sounds like it actually exceeded the expected max force that could be expected in the real world by 1.54 times, and that the design anticipated about 1.5x. So indeed, it hit dead-on the design expectation, rather than vastly exceeding it—but that's fine, because the design included a 50% margin of error (and one would hope, a conservative worst-case estimate).

Re: Door blows off Boeing 777X during stress test

#73

Post by ChuckMcM » Sat, Sep 07, 2019, 4:04 AM UTC

tempestn wrote: post #72

ChuckMcM wrote: post #70

Earlier quoted context omitted.

And it is, it is 154% or slightly more than 2.5x the 'design limit load'.

Slightly more than 1.5x you mean. And yeah, since the design limit load is already going to have a safety margin over the max anticipated load, as long as the test performs some amount beyond that design level, it's good. Edit: This is assuming the 'design level' is the level it was designed to withstand, which is how I would normally understand the term. Having watched the full video now though, it sounds like it ac…

This is the way I see it, you get to the design limit, that is 1x the design limit, then you up that by 100% so now you are at 2x the design limit, and then you go 54% more so you are at 2.54x the design limit.

Re: Door blows off Boeing 777X during stress test

#74

Post by Stevvo » Sat, Sep 07, 2019, 4:05 AM UTC

Comments here on this are like reddit comments, please shut the fuck up if you have nothing of value to add. I don't have downvote power so need to call all of you out. Simply quoting the article is not a valid comment; it does not generate discussion.

Re: Door blows off Boeing 777X during stress test

#75

Post by rolph » Sat, Sep 07, 2019, 4:07 AM UTC

Stevvo wrote: post #74

Comments here on this are like reddit comments, please shut the fuck up if you have nothing of value to add. I don't have downvote power so need to call all of you out. Simply quoting the article is not a valid comment; it does not generate discussion.

Thank You. This is my take on it:

the wings were bent in an extreme manner.

so you have a cylinder to a close approximation, with a hole in the side of it. Then you have two levers [wings] affixed to said cylinder, then you apply force to the levers, and distort the cylinder thus distorting the hole in the cylinder....

at this point i would invoke a topological parlour trick of making a quarter fall through a dime sized hole as an analogy.

https://prop-tricks.wonderhowto.com/how-to/do-large-coin-sma....

my hypothesis is that the entire airframe flexed causing the door frame to distort thus loosing its grip on the door panel

Re: Door blows off Boeing 777X during stress test

#76

Post by skosch » Sat, Sep 07, 2019, 4:24 AM UTC

ChuckMcM wrote: post #73

tempestn wrote: post #72

Earlier quoted context omitted.

Slightly more than 1.5x you mean. And yeah, since the design limit load is already going to have a safety margin over the max anticipated load, as long as the test performs some amount beyond that design level, it's good. Edit: This is assuming the 'design level' is the level it was designed to withstand, which is how I would normally understand the term. Having watched the full video now though, it sounds like it ac…

This is the way I see it, you get to the design limit, that is 1x the design limit, then you up that by 100% so now you are at 2x the design limit, and then you go 54% more so you are at 2.54x the design limit.

It's 154% of the design load, not 154% more than the design load. So 1.54×.

Re: Door blows off Boeing 777X during stress test

#77

Post by macoovacany » Sat, Sep 07, 2019, 4:27 AM UTC

kbenson wrote: post #19

cyberferret wrote: post #16

It's a stress test. You would expect things to break during a stress test. > "They loaded it up well beyond capacity and bent its wings in an extreme manner, in a way almost certain to never happen in the real world." Here is another video of a 777 wing test where it broke at 154% of the [s/normal/maximum theoretical/] load - a bit beyond what was expected by the engineering team. https://www.youtube.com/watch?v=Ai2H…

> Here is another video of a 777 wing test where it broke at 154% of the normal load I really hope you mean 154% of the max load, and I hope that max load is engineered to be far above what should be seen in actual service. 50% over the normal service load is not what I would consider extreme, and not something I would expect to be acceptable in an aircraft.

Ok, I'm hijacking this thread because there's some confusion about 'limit' load.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf...

Re: Door blows off Boeing 777X during stress test

#78

Post by Rapzid » Sat, Sep 07, 2019, 4:33 AM UTC

jrockway wrote: post #18

I like how their PR person says "Safety is the highest priority at Boeing." I feel like the reality is that "doing what our customers tell us so we sell more airplanes than Airbus" is their actual highest priority. I wonder how they fix that. I wonder if it's even possible for a publicly-traded corporation to do?

They will probably add another door so if one blows off they have a spare already.

Re: Door blows off Boeing 777X during stress test

#79

Post by kortilla » Sat, Sep 07, 2019, 4:39 AM UTC

ChuckMcM wrote: post #70

rtomanek wrote: post #67

Earlier quoted context omitted.

I would still expect the `maximum theoretical load` to be well above the `designed limit load`.

And it is, it is 154% or slightly more than 2.5x the 'design limit load'.

90% of $100 is not $190

Re: Door blows off Boeing 777X during stress test

#80

Post by cameldrv » Sat, Sep 07, 2019, 5:15 AM UTC

kbenson wrote: post #19

cyberferret wrote: post #16

It's a stress test. You would expect things to break during a stress test. > "They loaded it up well beyond capacity and bent its wings in an extreme manner, in a way almost certain to never happen in the real world." Here is another video of a 777 wing test where it broke at 154% of the [s/normal/maximum theoretical/] load - a bit beyond what was expected by the engineering team. https://www.youtube.com/watch?v=Ai2H…

> Here is another video of a 777 wing test where it broke at 154% of the normal load I really hope you mean 154% of the max load, and I hope that max load is engineered to be far above what should be seen in actual service. 50% over the normal service load is not what I would consider extreme, and not something I would expect to be acceptable in an aircraft.

Design limit load is for an aircraft at max allowable weight, with the max authorized g loading (often -1 to +2.5g) or the worst anticipated gusts (about 50 ft/sec depending on altitude). You then need to tack on 50% to get the required ultimate load.

50% is indeed not a huge safety margin like you'd get with a bridge or something, which is why you need trained professionals flying it and regular inspections. If you fly into a big enough thunderstorm, the wings can definitely come off. Of course a bigger safety margin would be nice, but every pound of wing spar is a pound less payload. If the FAA required 200% of design limit, flying would be significantly more expensive.