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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, i

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=Ai2HmvAXcU0 https://www.youtube.com/watch?v=Ai2HmvAXcU0

kbenson 7y ago
> 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.
- cyberferret 7y ago
  Sorry, I mistyped. It is indeed the maximum theoretical load as calculated by the engineering team.
  - dmix 7y ago
    Specifically from the video description: > This Boeing 777 wing was tested to destruction, finally breaking at one fifty four percent of the designed limit load.
    - rtomanek 7y ago
      I would still expect the `maximum theoretical load` to be well above the `designed limit load`.
      - ChuckMcM 7y ago
        And it is, it is 154% or slightly more than 2.5x the 'design limit load'.
        tempestn 7y ago
        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).
        ChuckMcM 7y ago
        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.
        skosch 7y ago
        It's 154% of the design load, not 154% more than the design load. So 1.54×.
        kortilla 7y ago
        90% of $100 is not $190
        ChuckMcM 7y ago
        Interestingly the 154% number seems to be gone from the article now The language is tricky, if you interpret it as I did, or 154% "more" than the design limit, then it is the design limit plus 1.54 more design limits. Like saying you salary is $100 and we're paying you 90% beyond your salary. Then you would expect to get $190. If you interpret it to be 154% "of" the design limit, then I would agree it would be 1.54x the design limit. Since other publications from Boeing, and Boeing staff at the "Future of Flight" museum in Everett have said that the planes are safer because they can withstand over twice their design limit, I read the 154% number as the amount "over" the limit. Since folks from Boeing read Hackernews, it would be great for one of them to chime in here with some clarification :-).
- macoovacany 7y ago
  Ok, I'm hijacking this thread because there's some confusion about 'limit' load. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/B283B63C33AC70B685256672004E98BB?OpenDocument http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf...
  - mkl 7y ago
    You're not hijacking it, just adding some contextual information, namely: "Strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety). Unless otherwise provided, prescribed loads are limit loads."
  - rntrg 7y ago
    Was that an airplane joke?
- cameldrv 7y ago
  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.
  - fluffything 7y ago
    > 50% is indeed not a huge safety margin like you'd get with a bridge or something Safety margins for bridges are like 25-50%.
    - cameldrv 7y ago
      That's interesting. I know that they used to be a lot more. Perhaps we should be glad that most of the bridges we drive over were built before FEM, and they just used a lot more steel. I wonder how well a bridge designed with a 25% safety margin is going to perform when it's poorly maintained for 50 years and rusting like a lot of bridges in the U.S.
      - fluffything 7y ago
        The reason this works is that the safety margins accumulate. You have a safety margin on: * the loading on the bridge, which can be higher than the calculated amount. * the resistance of the materials used, that can be lower than the requested amount. * the quality of the soil, * the lifespan of the bridge, * ... So the loading can be 25% percent higher, the materials can be 25% worse, the soil can be 25% worse, the lifespan can be 25% higher, ... and at the end you get a bridge that would still work if everything fails with a margin of 25%. If the loads are 30% higher, the bridge might or might not fail. Who knows. Even though there are many other safety factors, and the bridge probably won't fail, it was not designed for that. There might be a critical part somewhere that has a resistance that's 25% worse than what it should be, and it therefore can only support a 25% overload, and with 30% that part might fail. Bridges are designed to fail very slowly, loudly, and visibly, to avoid loss of functionality (e.g. when a bridge start to fail, this becomes obvious, and you still have months or years to sanitize the bridge). I expect airplanes to have much tighter safety margins (<15% or <10%). The loads are more accurately known, the materials are higher quality, everything passes more extensive quality assurance tests, weight is much more important and companies are willing to pay prime prices on materials, manufacturing, etc. to reduce it, etc. Safety margins aren't chosen arbitrarily. The job of a safety margin is to quantify an uncertainty, and with enough money thrown at each one, most of the uncertainties can be quite precisely quantified. Then it's the job of the designer to say "This plane should be in service for 50 years", and from the uncertainties and statistical analysis you can compute the highest load that the plane will receive in those 50 years with a certain quantified margin of error, and continue the design using that.
tpmx 7y ago
"A door blew off a Boeing 777X as the new plane was undergoing what was supposed to be its final structural inspection by federal regulators." It's literally the first sentence of the article. I doubt Boeing were pushing the envelopes further than the FAA required. And a door fell out.
- Groxx 7y ago
  The second, third, and fourth sentences seem to imply otherwise? >The test is meant to push the plane beyond its limits. Engineers had the plane pressurized and on the ground. 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. and also further down, more "not necessarily a normal test" evidence: >... The ultimate load test is the latest in a series of tests that Boeing has been conducting on this full-scale test airplane over the past several months."
  - inferiorhuman 7y ago
    The second, third, and fourth sentences seem to imply otherwise? Semantics. https://www.seattletimes.com/business/boeing-aerospace/door-blows-out-during-ground-test-on-boeing-777x-jet/ https://www.seattletimes.com/business/boeing-aerospace/door-... The Seattle Times explains it thusly: During the ultimate load test, the wings are then pulled upward. To pass the test and be certified, the wings must bend without breaking until the load on them reaches at least 150 percent of the normally expected load. … Sometimes this final test is continued beyond the 150 percent load target until a wing actually breaks. But not always. … This time, however, though the wings did not give way; it was one of the doors that failed — an outcome that is definitely not supposed to happen.
    - ImprovedSilence 7y ago
      I mean, when it comes down to it, I’d rather lose a door than a wing though, right...?
      - 7y ago
jussij 7y ago
> You would expect things to break during a stress test. Except, the whole point of the test is to stress the plane and to have nothing break. The test is designed to make sure the aircraft has built-in safety (i.e. is over engineered). When the A380 was attempting to earn it's certification it failed a similar static wing test: http://www.airmech.co.uk/forums/showthread.php/5340-A380-Wing-Ruptures-In-Stress-Tests http://www.airmech.co.uk/forums/showthread.php/5340-A380-Win...
- txcwpalpha 7y ago
  >Except, the whole point of the test is to stress the plane and to have nothing break. What? No it's not. The entire point of these tests is specifically to break things. If nothing breaks, they did not perform the test correctly. >When the A380 was attempting to earn it's certification it failed a similar static wing test: No, it didn't. It passed the test handily. The wing broke well beyond the max load limit, which is what they were testing for. edit for the sake of being less of an argumentative asshole: I see where you're coming from when you say that it was a 'failure'. However, what I mean to say is that while the wings failed in the test, the failure was intentional, and the data gathered during the test was exactly what was needed to prove that the A380's wings were strong enough for certification, and the A380 was certified based on the results of this test. In my mind, that means the test passed.
  - jussij 7y ago
    The first time the A380 tried the test it failed. Read the link. And yes it did eventually pass that wing test only because if it had not it would not never have been certified.
    - txcwpalpha 7y ago
      >The first time the A380 tried the test it failed. Read the link. I suggest you read it. The A380 did not fail. It says so in the link you provided.
      - 7y ago
cyberferret 7y ago
Also - need to ensure that all testing methodologies were up to scratch. Here is an article about a KC-135 pressure test that ended up making the plane pop like a balloon [0] - all because the pressure gauge used by the tester didn't have a 'stop' peg and he missed the fact that the needle had cycled around. A door hatch from the aircraft was found 70 yards away. [0] - https://theaviationgeekclub.com/time-kc-135-stratotanker-aircraft-exploded-failed-pressure-test/ https://theaviationgeekclub.com/time-kc-135-stratotanker-air...
anigbrowl 7y ago
That's...not something any client wants to hear.
- Groxx 7y ago
  if they're interested in knowing non-theoretical failure limits, and how it behaves under failure: yes, of course they want to hear that.
RcouF1uZ4gsC 7y ago
Good point about it being normal for stuff to break during a stress test. However, it seems the door blowing off is not something that normally happens and that to me is more worrisome than if it was a common failure when the stresses greatly exceed the theoretical limits. >Former Boeing Engineer Dr. Todd Curtis runs Airsafe.com and said this doesn't happen often. "I've never heard of a case where a door popped off like this during a stress test before," he said. "Doesn't mean it hasn't happened before, I'm just not aware of it."
ajross 7y ago
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.
- inferiorhuman 7y ago
  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.
  - dhimes 7y ago
    in theory, the 777X is just a variant of the 777 Uh oh. Haven't we seen this story before with a different model (cough 737 cough)?
raverbashing 7y ago
It depends on the stress test If you're testing it up to the limit then no, it is not expected. But if you're pushing it beyond the design limit then yes, it is expected to break. Some wing tests are done beyond the limit, some are done below the limit (non-destructive tests cost less, that's why they're preferred, but for a new design they might just push it beyond the limit to see when does it effectively fail)
97b683f8 7y ago
If I ever write a library to perform stress tests, I'll call it one-fifty-four.
Havoc 7y ago
>You would expect things to break during a stress test. Given the stunned silence and halting of further testing I'm guessing this wasn't a stress it till breaking type stress test

kbenson 7y ago

> 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.

cyberferret 7y ago
Sorry, I mistyped. It is indeed the maximum theoretical load as calculated by the engineering team.
- dmix 7y ago
  Specifically from the video description: > This Boeing 777 wing was tested to destruction, finally breaking at one fifty four percent of the designed limit load.
  - rtomanek 7y ago
    I would still expect the `maximum theoretical load` to be well above the `designed limit load`.
    - ChuckMcM 7y ago
      And it is, it is 154% or slightly more than 2.5x the 'design limit load'.
      - tempestn 7y ago
        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).
        ChuckMcM 7y ago
        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.
        skosch 7y ago
        It's 154% of the design load, not 154% more than the design load. So 1.54×.
      - kortilla 7y ago
        90% of $100 is not $190
        ChuckMcM 7y ago
        Interestingly the 154% number seems to be gone from the article now The language is tricky, if you interpret it as I did, or 154% "more" than the design limit, then it is the design limit plus 1.54 more design limits. Like saying you salary is $100 and we're paying you 90% beyond your salary. Then you would expect to get $190. If you interpret it to be 154% "of" the design limit, then I would agree it would be 1.54x the design limit. Since other publications from Boeing, and Boeing staff at the "Future of Flight" museum in Everett have said that the planes are safer because they can withstand over twice their design limit, I read the 154% number as the amount "over" the limit. Since folks from Boeing read Hackernews, it would be great for one of them to chime in here with some clarification :-).
macoovacany 7y ago
Ok, I'm hijacking this thread because there's some confusion about 'limit' load. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/B283B63C33AC70B685256672004E98BB?OpenDocument http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf...
- mkl 7y ago
  You're not hijacking it, just adding some contextual information, namely: "Strength requirements are specified in terms of limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by prescribed factors of safety). Unless otherwise provided, prescribed loads are limit loads."
- rntrg 7y ago
  Was that an airplane joke?
cameldrv 7y ago
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.
- fluffything 7y ago
  > 50% is indeed not a huge safety margin like you'd get with a bridge or something Safety margins for bridges are like 25-50%.
  - cameldrv 7y ago
    That's interesting. I know that they used to be a lot more. Perhaps we should be glad that most of the bridges we drive over were built before FEM, and they just used a lot more steel. I wonder how well a bridge designed with a 25% safety margin is going to perform when it's poorly maintained for 50 years and rusting like a lot of bridges in the U.S.
    - fluffything 7y ago
      The reason this works is that the safety margins accumulate. You have a safety margin on: * the loading on the bridge, which can be higher than the calculated amount. * the resistance of the materials used, that can be lower than the requested amount. * the quality of the soil, * the lifespan of the bridge, * ... So the loading can be 25% percent higher, the materials can be 25% worse, the soil can be 25% worse, the lifespan can be 25% higher, ... and at the end you get a bridge that would still work if everything fails with a margin of 25%. If the loads are 30% higher, the bridge might or might not fail. Who knows. Even though there are many other safety factors, and the bridge probably won't fail, it was not designed for that. There might be a critical part somewhere that has a resistance that's 25% worse than what it should be, and it therefore can only support a 25% overload, and with 30% that part might fail. Bridges are designed to fail very slowly, loudly, and visibly, to avoid loss of functionality (e.g. when a bridge start to fail, this becomes obvious, and you still have months or years to sanitize the bridge). I expect airplanes to have much tighter safety margins (<15% or <10%). The loads are more accurately known, the materials are higher quality, everything passes more extensive quality assurance tests, weight is much more important and companies are willing to pay prime prices on materials, manufacturing, etc. to reduce it, etc. Safety margins aren't chosen arbitrarily. The job of a safety margin is to quantify an uncertainty, and with enough money thrown at each one, most of the uncertainties can be quite precisely quantified. Then it's the job of the designer to say "This plane should be in service for 50 years", and from the uncertainties and statistical analysis you can compute the highest load that the plane will receive in those 50 years with a certain quantified margin of error, and continue the design using that.

tpmx 7y ago

"A door blew off a Boeing 777X as the new plane was undergoing what was supposed to be its final structural inspection by federal regulators." It's literally the first sentence of the article. I doubt Boeing were pushing the envelopes further than the FAA required. And a door fell out.

Groxx 7y ago
The second, third, and fourth sentences seem to imply otherwise? >The test is meant to push the plane beyond its limits. Engineers had the plane pressurized and on the ground. 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. and also further down, more "not necessarily a normal test" evidence: >... The ultimate load test is the latest in a series of tests that Boeing has been conducting on this full-scale test airplane over the past several months."
- inferiorhuman 7y ago
  The second, third, and fourth sentences seem to imply otherwise? Semantics. https://www.seattletimes.com/business/boeing-aerospace/door-blows-out-during-ground-test-on-boeing-777x-jet/ https://www.seattletimes.com/business/boeing-aerospace/door-... The Seattle Times explains it thusly: During the ultimate load test, the wings are then pulled upward. To pass the test and be certified, the wings must bend without breaking until the load on them reaches at least 150 percent of the normally expected load. … Sometimes this final test is continued beyond the 150 percent load target until a wing actually breaks. But not always. … This time, however, though the wings did not give way; it was one of the doors that failed — an outcome that is definitely not supposed to happen.
  - ImprovedSilence 7y ago
    I mean, when it comes down to it, I’d rather lose a door than a wing though, right...?
    - 7y ago

jussij 7y ago

> You would expect things to break during a stress test. Except, the whole point of the test is to stress the plane and to have nothing break. The test is designed to make sure the aircraft has built-in safety (i.e. is over engineered). When the A380 was attempting to earn it's certification it failed a similar static wing test: http://www.airmech.co.uk/forums/showthread.php/5340-A380-Wing-Ruptures-In-Stress-Tests http://www.airmech.co.uk/forums/showthread.php/5340-A380-Win...

txcwpalpha 7y ago
>Except, the whole point of the test is to stress the plane and to have nothing break. What? No it's not. The entire point of these tests is specifically to break things. If nothing breaks, they did not perform the test correctly. >When the A380 was attempting to earn it's certification it failed a similar static wing test: No, it didn't. It passed the test handily. The wing broke well beyond the max load limit, which is what they were testing for. edit for the sake of being less of an argumentative asshole: I see where you're coming from when you say that it was a 'failure'. However, what I mean to say is that while the wings failed in the test, the failure was intentional, and the data gathered during the test was exactly what was needed to prove that the A380's wings were strong enough for certification, and the A380 was certified based on the results of this test. In my mind, that means the test passed.
- jussij 7y ago
  The first time the A380 tried the test it failed. Read the link. And yes it did eventually pass that wing test only because if it had not it would not never have been certified.
  - txcwpalpha 7y ago
    >The first time the A380 tried the test it failed. Read the link. I suggest you read it. The A380 did not fail. It says so in the link you provided.
    - 7y ago

cyberferret 7y ago

Also - need to ensure that all testing methodologies were up to scratch. Here is an article about a KC-135 pressure test that ended up making the plane pop like a balloon [0] - all because the pressure gauge used by the tester didn't have a 'stop' peg and he missed the fact that the needle had cycled around. A door hatch from the aircraft was found 70 yards away. [0] - https://theaviationgeekclub.com/time-kc-135-stratotanker-aircraft-exploded-failed-pressure-test/ https://theaviationgeekclub.com/time-kc-135-stratotanker-air...

anigbrowl 7y ago

That's...not something any client wants to hear.

Groxx 7y ago
if they're interested in knowing non-theoretical failure limits, and how it behaves under failure: yes, of course they want to hear that.

RcouF1uZ4gsC 7y ago

Good point about it being normal for stuff to break during a stress test. However, it seems the door blowing off is not something that normally happens and that to me is more worrisome than if it was a common failure when the stresses greatly exceed the theoretical limits. >Former Boeing Engineer Dr. Todd Curtis runs Airsafe.com and said this doesn't happen often. "I've never heard of a case where a door popped off like this during a stress test before," he said. "Doesn't mean it hasn't happened before, I'm just not aware of it."

ajross 7y ago

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.

inferiorhuman 7y ago
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.
- dhimes 7y ago
  in theory, the 777X is just a variant of the 777 Uh oh. Haven't we seen this story before with a different model (cough 737 cough)?

raverbashing 7y ago

It depends on the stress test If you're testing it up to the limit then no, it is not expected. But if you're pushing it beyond the design limit then yes, it is expected to break. Some wing tests are done beyond the limit, some are done below the limit (non-destructive tests cost less, that's why they're preferred, but for a new design they might just push it beyond the limit to see when does it effectively fail)

97b683f8 7y ago

If I ever write a library to perform stress tests, I'll call it one-fifty-four.

Havoc 7y ago

>You would expect things to break during a stress test. Given the stunned silence and halting of further testing I'm guessing this wasn't a stress it till breaking type stress test