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> 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 e

> 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 :-).
        dmix 7y ago
        It’s in the above Boeing video not the article.
        mkl 7y ago
        It's not a matter of interpretation or tricky language. The video says "of" [1] so it's 1.54 times the design limit. [1] https://youtu.be/Ai2HmvAXcU0?t=45 https://youtu.be/Ai2HmvAXcU0?t=45
        kortilla 7y ago
        The video was clear and left no room for interpretation. Planes are safer because “they can withstand twice their design limit” is senseless. The 2x factor you are thinking of is the design limit. The design limit has all of the huge safety margins built in for the normal load limits. The planes are designed to take at least 2x the max normal loads.
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.

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 :-).
        dmix 7y ago
        It’s in the above Boeing video not the article.
        mkl 7y ago
        It's not a matter of interpretation or tricky language. The video says "of" [1] so it's 1.54 times the design limit. [1] https://youtu.be/Ai2HmvAXcU0?t=45 https://youtu.be/Ai2HmvAXcU0?t=45
        kortilla 7y ago
        The video was clear and left no room for interpretation. Planes are safer because “they can withstand twice their design limit” is senseless. The 2x factor you are thinking of is the design limit. The design limit has all of the huge safety margins built in for the normal load limits. The planes are designed to take at least 2x the max normal loads.

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.