morrisond
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Fri Nov 29, 2019 9:05 pm

d8s wrote:
morrisond wrote:
Yes they are expected to fail - I think the bigger part of the story will be Boeing downplaying the story.

Pictures https://www.seattletimes.com/business/b ... uffer_tw_m


Really? "the test failed so explosively at just 1% shy of meeting federal requirements". What is there to cover up?


Have your read through this thread and seen the reactions?

And BTW - I tried to retract that statement after reading the Seattle Times article and Boeing's original statement as I'm sure many on here should have read by now - But it's been deleted 3x already.

It was based off seeing it on CNBC before fully reading the article.

If I get a good explanation from someone on why they tested at 10 PSI then I'm good to go.
 
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Fri Nov 29, 2019 9:07 pm

OldAeroGuy wrote:
It is doubtful that the 3.75 g structural loading test was being performed at a loading of 3.75 X 464,400 lb. Therefore your supposition about the fuselage pressurization being representative of flying at 43,100 ft is probably incorrect. The critical structural loading would be no lower than 3.75 X MZFW which would mean the pressurization differential would be for a lower altitude than 43,100 ft where MZFW or higher would be a valid cruise weight.


I didnt understand why the 77X was being done at 10 psi where the A350 was done at 18 psi (both having the same max altitude and same cabin pressure). If the 10 psi is at 150%, that would indicate a cruise altitude of 26,600 ft for a 6000 ft cabin altitude.
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sat Nov 30, 2019 2:53 am

morrisond wrote:
OldAeroGuy wrote:
zeke wrote:

The 777 currently has a maximum altitude of 43100 ft, which is a pressure of 2.34 psi in a standard atmosphere, if it maintains a 8000 ft (10.92 psi is the pressure at 8000 ft in a standard atmosphere) cabin at that altitude, the maximum pressure diff is 10.92-2.34=8.58 psi. The maximum diff if the pressure difference on the surface of the pressure vessel, the pressure difference between 41300 ft and 8000 ft.

150% of 8.58 psi is 12.87, this test failed at 10 psi according to the media reports.

With the 777X they wanted to maintain a maximum cabin of 6000 ft (11.78 psi is the pressure at 6000 ft in a standard atmosphere). So the maximum diff required is 11.78-2.34 =9.44 psi, which is very close to the failure level reported of 10 psi, only around a 6% safety margin.

So in my view the Boeing statement was deliberately misleading. They had been given the opportunity a number of times to get ahead of this, instead have downplayed this to a level which I think is which is generous to call it misleading.


You can't ignore the real world operational weight of a 777-9 flying at 43,100 ft. Let's compute what that weight might actually be.

Similar to the 777-300ER, the 777-9 will have an operational cruise speed of about 0.84M. At 43,100 ft, the resulting dynamic pressure will be 167 psf.

Using CL = 0.5 and a wing area of 5562 sq ft., the resulting 777-9 cruise weight would be 464,400 lb. This weight is 21% less than the MZFW of 562,000lb.

It is doubtful that the 3.75 g structural loading test was being performed at a loading of 3.75 X 464,400 lb. Therefore your supposition about the fuselage pressurization being representative of flying at 43,100 ft is probably incorrect. The critical structural loading would be no lower than 3.75 X MZFW which would mean the pressurization differential would be for a lower altitude than 43,100 ft where MZFW or higher would be a valid cruise weight.


Hi OldAeroGuy,

As one of wisest posters on this site maybe you can answer the following. No one seems to know.

By pressurizing to 10 PSI - more than they had too apparently - would that have made it easier to pass the test or harder?

Please try to put it in layman terms for those of us who are not engineers.

Much Appreciated.


It's not about making the test easier to pass. It's about replicating some set of conditions the engineers were targeting.

Yes, you can reduce compression driven buckling with a higher pressure but we typically size stuff to compression buckle anyways (ie dump the load into surrounding structure). Shear buckling gets more attention.

We size things to buckle at limit load. Its not a failure as long as it doesnt cause permanent deformation (FARS cover this).

But it doesn't even matter if it would have or not, it's the condition they were testing for and had predictions on.

Let me say this plainly, had they done the exact same scenario but only gone to 8psi it would not have failed. That's because you have to consider the full state of stress, not just the compression caused by the down bend of the fuselage. You have to note that it's also an elevated hoop tension stress.

Lastly let me just state that buckling is a stability failure but not a structural failure. Even with permanent deformation you should still remain pressurized. You'd just have wrinkles in the skins.

The B52 for instance has buckled fuselage skins while sitting on the tarmac due to the weight of its wings. But when it takes off those buckles all come out. Pretty cool actually. But scary if you see it on the ground with no idea it's supposed to be that way.

TLDR: In this case the pressure would result in a worse condition, but even if it hadn't it doesn't matter with respect to the test. The test was representative of some condition the engineers were targeting for some reason. All that matters is that it failed almost exactly when they thought it would. Which means all their sizing efforts should be correct. This validates their FEMS. That's good.
 
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sat Nov 30, 2019 3:19 am

trpmb6 wrote:
Let me say this plainly, had they done the exact same scenario but only gone to 8psi it would not have failed. That's because you have to consider the full state of stress, not just the compression caused by the down bend of the fuselage. You have to note that it's also an elevated hoop tension stress.


I understand that it’s a combined loads case, I said as much above. If it had just been wing bending or pressurisation it would not have failed, it failed with the combined loads.

trpmb6 wrote:
Lastly let me just state that buckling is a stability failure but not a structural failure. Even with permanent deformation you should still remain pressurized. You'd just have wrinkles in the skins.


That does not look like a buckling failure to me, it looks like it failed on the fasteners. The term I think you should be using is post buckling, not buckling.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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SomebodyInTLS
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sat Nov 30, 2019 3:42 am

zeke wrote:
Wing loading is transferred into the fuselage where the wing meets the fuselage, this is the site of this failure. As the load is transferred into the fuselage skin will start to buckle. Add the pressurisation loads onto that you get the combined failure case.


I responded on this topic to Keesje's post with the embedded image... which seems to have been moderated for some reason.

Anyway, I mentioned that for me the question is whether the damage is the cause or result of the door coming off. If the fuselage ruptured and that led to the door departing, then that is quite serious - albeit right on the edge of the test envelope so should be possible to mitigate through calculation.

If, on the other hand, a door latch failed for example and the departing door caused the fuselage to fail, then that is a straightforward fix to the door.

The thing is that any failure under those conditions will look catastrophic.
"As with most things related to aircraft design, it's all about the trade-offs and much more nuanced than A.net likes to make out."
 
maint123
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 3:52 am

At sea level , atmospheric pressure is 14.6 psi.
A car tyres normal pressure is 2 bar or 30 psi.
Testing with 10 psi means a differential pressure of around 4 psi, wrt the outside(14psi). Buckling load.
I understand that at high altitudes the pressure difference between cabin and outside would increase in the other direction, (at 35000 ft the ambient pressure is 3.5 psi).
So why is 10 psi being considered a high pressure for testing ? Because of the thin aluminium sheets ?
 
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 3:53 am

I suspect the fuselage failed along a join, the door I don’t think was the primary mode.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sat Nov 30, 2019 4:19 am

zeke wrote:
trpmb6 wrote:
Let me say this plainly, had they done the exact same scenario but only gone to 8psi it would not have failed. That's because you have to consider the full state of stress, not just the compression caused by the down bend of the fuselage. You have to note that it's also an elevated hoop tension stress.


I understand that it’s a combined loads case, I said as much above. If it had just been wing bending or pressurisation it would not have failed, it failed with the combined loads.

trpmb6 wrote:
Lastly let me just state that buckling is a stability failure but not a structural failure. Even with permanent deformation you should still remain pressurized. You'd just have wrinkles in the skins.


That does not look like a buckling failure to me, it looks like it failed on the fasteners. The term I think you should be using is post buckling, not buckling.


Sorry, I wasn't really replying to your analysis because your analysis is irrelevant. I was primarily responding to morrisons.

Buckling causes other members to become loaded which causes those members to eventually reach their column buckling or crippling limits and causes instability failures which can cause separation of parts due to large deformations.

But yes, that's not what happened here based on what I see in the pictures. Hence my entire post. People were asking about if increasing pressure could relieve the structure and it's not that simple of an answer.

What matters is they came within a percent of their target. Indicating they sized the structure to this load. That's what matters.

The pressure that they used doesn't matter because it's not at any of the altitudes you pointed out. Its some envelope condition at some random altitude in the mission that correlates with the max downbend of the fuselage and max upbend of the wing. Probably extremely conservative Vdive condition with a gust.

To your last post, the failure was in the cargo door surround. Not surprising, that's a massive cutout with lots of load redistribution.

Now, I feel I should address your "boeing is deliberately being misleading". On what basis? The pressure is dependent on some specific condition they plucked out of thousands and thousands of load cases to test. Picture a graph with lots of dots plotted all around it. This condition they tested produced an exact set of circumstances they were interested in. Nothing more nothing less. Stop trying to look for something nefarious here. To imply there was something evil and nefarious was going on is to sully the ethics and dignity of thousands of engineers. And if you are going to go down that road you better go find a cave to live in because engineers dictate every safety standard you deal with every single day. From the sizing of the frames in your home's roof to the elevator you take in your apartment building to the car you drive and the trains and planes you ride.

The amount of engineer bashing on those site annoys the hell out of me. I mean holy hell they got within 1 percent of their target! THINK ABOUT THAT! A massively complex system with millions of variables and they got within ONE FREAKKNG PERCENT and you guys sit here with holier than thou attitudes. Get a freaking life.
 
JayinKitsap
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 4:42 am

zeke wrote:
I suspect the fuselage failed along a join, the door I don’t think was the primary mode.


I agree, the fasteners would be at peak load in both tension and shear. This join is very close to the wing box which is a complicated area.
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 5:33 am

JayinKitsap wrote:
zeke wrote:
I suspect the fuselage failed along a join, the door I don’t think was the primary mode.


I agree, the fasteners would be at peak load in both tension and shear. This join is very close to the wing box which is a complicated area.


Based on the pictures the fasteners did not fail. Generally we don't size for fasteners to fail in the aircraft industry. We size the material to fail in bearing. Fuselage fasteners don't see much tension. Just lots of load redistribution in this area due to the cargo door cutout. You can see all the doubler reinforcements in the picture. Failure started up above the picture frame and progressed down into the door surround. Exactly how I'd expect it to fail.
 
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SheikhDjibouti
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 1:47 pm

maint123 wrote:
At sea level , atmospheric pressure is 14.6 psi.
A car tyres normal pressure is 2 bar or 30 psi.
Testing with 10 psi means a differential pressure of around 4 psi, wrt the outside(14psi). Buckling load.
I understand that at high altitudes the pressure difference between cabin and outside would increase in the other direction, (at 35000 ft the ambient pressure is 3.5 psi).
So why is 10 psi being considered a high pressure for testing ? Because of the thin aluminium sheets ?

I wondered this myself, but the simple answer must be that in the case of tire pressure gauges, they are measuring differential, not absolute figures.

The proof of this is to test a flat tire, or just present the pressure gauge to the air around you; it reads zero, and yet logically it must be matched to ambient surroundings (14.6psi)
Following this, a tire at "30psi" is actually full of air at 46.4psi absolute.

The implication in the case of Boeing, is that the fuselage was pressurised to a differential of 10psi, i.e. above the ambient 14.6psi within the surrounding hangar.

Either that, or they somehow transformed the entire hangar into a vacuum flask. :shakehead:

But I'm just an ordinary dude making my best guess - I don't have any actual facts..... :lol:
Nothing to see here; move along please.
 
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Polot
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 2:03 pm

SheikhDjibouti wrote:
maint123 wrote:
At sea level , atmospheric pressure is 14.6 psi.
A car tyres normal pressure is 2 bar or 30 psi.
Testing with 10 psi means a differential pressure of around 4 psi, wrt the outside(14psi). Buckling load.
I understand that at high altitudes the pressure difference between cabin and outside would increase in the other direction, (at 35000 ft the ambient pressure is 3.5 psi).
So why is 10 psi being considered a high pressure for testing ? Because of the thin aluminium sheets ?

I wondered this myself, but the simple answer must be that in the case of tire pressure gauges, they are measuring differential, not absolute figures.

The proof of this is to test a flat tire, or just present the pressure gauge to the air around you; it reads zero, and yet logically it must be matched to ambient surroundings (14.6psi)
Following this, a tire at "30psi" is actually full of air at 46.4psi absolute.

The implication in the case of Boeing, is that the fuselage was pressurised to a differential of 10psi, i.e. above the ambient 14.6psi within the surrounding hangar.

Either that, or they somehow transformed the entire hangar into a vacuum flask. :shakehead:

But I'm just an ordinary dude making my best guess - I don't have any actual facts..... :lol:

Yes, it is the differential. Vacuuming the interior to 10 psi doesn’t make any sense, that is the opposite of the stress the fuselage would normally be facing (higher interior pressure vs outside).
 
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crimsonchin
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 2:14 pm

When a company is in the news having been recently accused of not being straightforward with a software that may have contributed to the deaths of 300+ passengers, everything about the company is news, unfairly or not. That's what is happening here.
 
maint123
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 2:22 pm

SheikhDjibouti wrote:
maint123 wrote:
At sea level , atmospheric pressure is 14.6 psi.
A car tyres normal pressure is 2 bar or 30 psi.
Testing with 10 psi means a differential pressure of around 4 psi, wrt the outside(14psi). Buckling load.
I understand that at high altitudes the pressure difference between cabin and outside would increase in the other direction, (at 35000 ft the ambient pressure is 3.5 psi).
So why is 10 psi being considered a high pressure for testing ? Because of the thin aluminium sheets ?

I wondered this myself, but the simple answer must be that in the case of tire pressure gauges, they are measuring differential, not absolute figures.

The proof of this is to test a flat tire, or just present the pressure gauge to the air around you; it reads zero, and yet logically it must be matched to ambient surroundings (14.6psi)
Following this, a tire at "30psi" is actually full of air at 46.4psi absolute.

The implication in the case of Boeing, is that the fuselage was pressurised to a differential of 10psi, i.e. above the ambient 14.6psi within the surrounding hangar.

Either that, or they somehow transformed the entire hangar into a vacuum flask. :shakehead:

But I'm just an ordinary dude making my best guess - I don't have any actual facts..... :lol:

Yup you are right, it's differential pressure. Googled it.
When tire pressure is 30 psi, it's differential, like we normally check with a barometer for low pressure gases. One side is open to the atmosphere.
So absolute pressure of tyre is 45 psi.
So checking at 10 psi means the plane body just has to take a pressure of 10 psi differential. A rubber tyre is having a differential pressure of 30 psi.
So my question still stands, that's a pretty low pressure ?
 
kalvado
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 2:39 pm

maint123 wrote:
At sea level , atmospheric pressure is 14.6 psi.
A car tyres normal pressure is 2 bar or 30 psi.
Testing with 10 psi means a differential pressure of around 4 psi, wrt the outside(14psi). Buckling load.
I understand that at high altitudes the pressure difference between cabin and outside would increase in the other direction, (at 35000 ft the ambient pressure is 3.5 psi).
So why is 10 psi being considered a high pressure for testing ? Because of the thin aluminium sheets ?

psig and psia are slightly different things. common use of psi for psig (gauge) refers to pressure differential, not psia (absolute) pressure. So,

At sea level , atmospheric pressure is 14.6 psia. A car tyres normal pressure is 2 bar or 30 psig, or 3 atm / 45 psia
 
kalvado
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 2:49 pm

maint123 wrote:
So checking at 10 psi means the plane body just has to take a pressure of 10 psi differential. A rubber tyre is having a differential pressure of 30 psi.
So my question still stands, that's a pretty low pressure ?

10 psig - differential - for plane body means that at FL400 (12 km, air pressure is 20% of that on the ground, or about 3 psia), same stress would be created by cabin altitude of less than 1000 feet.
That is a fairly reasonable value above expected conditions - which is 7-8 psia for 6-8k feet cabin altitude.
Numbers are ballpark, using this graph: https://www.engineeringtoolbox.com/docs ... essure.png
 
787X30
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 2:58 pm

crimsonchin wrote:
... may have contributed to the deaths of 300+ passengers, ...

Nah... let's say "to an issue that arose to less than one percent of max's pax's dignity", shall we.

While I don't like the efforts to manifest that "one-percent-criterion" into our heads - when 1.48 reached from 1.50 required represents 98,7%, or 1,3% from target, thus outside a 1%-interval.

I'd not lose my nerve over that, but the experts seem to do.
 
kalvado
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 3:13 pm

787X30 wrote:
crimsonchin wrote:
... may have contributed to the deaths of 300+ passengers, ...

Nah... let's say "to an issue that arose to less than one percent of max's pax's dignity", shall we.

While I don't like the efforts to manifest that "one-percent-criterion" into our heads - when 1.48 reached from 1.50 required represents 98,7%, or 1,3% from target, thus outside a 1%-interval.

I'd not lose my nerve over that, but the experts seem to do.

Flying machines - planes, and even more so space equipment - are designed at the very edge of performance to save weight. 150% for a newly manufactured test article is fairly conservative - 50% reserved for manufacturing imprefections and fatigue to ensure 100% performance left for ops at the end of service life.
A true compromise for 1% performance lack on new article would be 5-10% service life reduction - to stay away from back wall of the bathtub curve, where problems start growing exponentially. Which may - or may not - be a big deal, depending on use pattern.
Oh, I think we just saw how that worked in another plane..
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 3:53 pm

Still don't understand why you guys are hung up on the pressure thing. Or freaking out about being short 1 percent.

If they had gone over by one or two percent you'd be claiming they didn't save enough weight and thus it will impact the consumer in raised ticket prices due to extra fuel costs.

Absolutely nothing improper with what they've done here. And this load case they tested is extremely conservative. You keep talking about 150% of limit load but seem to forget the superposition of the cases they used should never happen.

I listed in a previous post why I think they tested this case. Still valid.
 
oschkosch
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 3:56 pm

Does anyone know why they sort of "hid" the major fuselage damage?
 
kalvado
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 4:17 pm

oschkosch wrote:
Does anyone know why they sort of "hid" the major fuselage damage?

Because general public can get (and actually gets) agitated over this stuff. Boeing has enough problems to handle; this is not the biggest one. It will be resolved to the satisfaction of engineering experts at Boeing, faa and customer airlines. That is honestly the end of story: some delay and resolved problem.
Boeing is not known for the openness, and being in a spotlight doesn't encourage being more open
 
Ertro
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 4:35 pm

trpmb6 wrote:
Still don't understand why you guys are hung up on the pressure thing. Or freaking out about being short 1 percent.

If they had gone over by one or two percent you'd be claiming they didn't save enough weight and thus it will impact the consumer in raised ticket prices due to extra fuel costs.

Absolutely nothing improper with what they've done here. And this load case they tested is extremely conservative. You keep talking about 150% of limit load but seem to forget the superposition of the cases they used should never happen.

I listed in a previous post why I think they tested this case. Still valid.


If Boeing would have calculated that this exact spot on the plane can fail in this specific way just above 150% and it failed at 149% then that would not be a problem. However this seems not to be the case.

Boeing statement talks about "an issue arose", "suspend testing", "root-cause assessment over the coming weeks".

Those quotes seem to suggest that this was unexpected and that Boeing does not know how it failed. If they do not know how it failed then they could not possibly have designed it to fail at 151%. If a wingspar snaps during this test at 149% then Boeing or Airbus are not going to put out a statement like Boeing did here. The statement is going to be "Test highly succesful. The wing snapped at 149% in exactly the way it was predicted to fail at 150% so pretty darn close. We just add a tiny bit of material and we are done". And everybody is happy. Boeing clearly knows what they are doing. Now the fact that it failed at 149% seems like just a random accident. Manufacturing some spot which Boeing does not know is the rootcause point of failure slightly differently could have made this spot fail at 110% load instead.

It seems Boeing still does not know how it failed. Highly knowledgeable Boeing employees are still going on wild tangents on messageboards speculating how it could have failed. If Boeing has any idea how it failed and management does not distribute this clear information inside Boeing so that employees know not to do that that is very strange. If I would be Boeing managment then this would be a place where I would instill confidence in Boeing engineers by putting out some statement that tells the world that Boeing knows what they are doing although there is no law or other requirement to do so. It would just benefit Boeing to do so.
 
SanDiegoLover
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sat Nov 30, 2019 4:36 pm

Checklist787 wrote:
seahawk wrote:

Notice the difference, in the Airbus case the damage was limited to a specific area of the wing. The pics of the fuselage show many structural components broken.


With a little bit of glue and tape
It should be fine... :scratchchin:


You forgot chewing gum and baling wire. ;)
 
2175301
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 4:41 pm

kalvado wrote:
oschkosch wrote:
Does anyone know why they sort of "hid" the major fuselage damage?

Because general public can get (and actually gets) agitated over this stuff. Boeing has enough problems to handle; this is not the biggest one. It will be resolved to the satisfaction of engineering experts at Boeing, faa and customer airlines. That is honestly the end of story: some delay and resolved problem.
Boeing is not known for the openness, and being in a spotlight doesn't encourage being more open


As an engineer who has done testing (although not on aircraft): Test results are rarely published anywhere by anyone because most people just don't understand things. Publishing various pictures or results usually means many hours of explorations... when no explanations are actually needed for the test engineers.

This would be like disclosing to the public everything that happens in the "bedroom" and the "bathroom" Too much information - and not really relevant to much of life (although it may be useful and appropriate to tell a Medical Doctor or Nurse, etc). All companies testing things go through failures during testing (as engineers we are very interested in when and where things will fail). The final visual results to the device being tested often looks very bad to the uniformed. TMA applies. That is why such pictures are not normally released. Boeing, nor anyone else, is required to - or even expected to - release such pictures.

Have a great day,
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 4:54 pm

Ertro wrote:
trpmb6 wrote:
Still don't understand why you guys are hung up on the pressure thing. Or freaking out about being short 1 percent.

If they had gone over by one or two percent you'd be claiming they didn't save enough weight and thus it will impact the consumer in raised ticket prices due to extra fuel costs.

Absolutely nothing improper with what they've done here. And this load case they tested is extremely conservative. You keep talking about 150% of limit load but seem to forget the superposition of the cases they used should never happen.

I listed in a previous post why I think they tested this case. Still valid.


If Boeing would have calculated that this exact spot on the plane can fail in this specific way just above 150% and it failed at 149% then that would not be a problem. However this seems not to be the case.

Boeing statement talks about "an issue arose", "suspend testing", "root-cause assessment over the coming weeks".

Those quotes seem to suggest that this was unexpected and that Boeing does not know how it failed. If they do not know how it failed then they could not possibly have designed it to fail at 151%. If a wingspar snaps during this test at 149% then Boeing or Airbus are not going to put out a statement like Boeing did here. The statement is going to be "Test highly succesful. The wing snapped at 149% in exactly the way it was predicted to fail at 150% so pretty darn close. We just add a tiny bit of material and we are done". And everybody is happy. Boeing clearly knows what they are doing. Now the fact that it failed at 149% seems like just a random accident. Manufacturing some spot which Boeing does not know is the rootcause point of failure slightly differently could have made this spot fail at 110% load instead.

It seems Boeing still does not know how it failed. Highly knowledgeable Boeing employees are still going on wild tangents on messageboards speculating how it could have failed. If Boeing has any idea how it failed and management does not distribute this clear information inside Boeing so that employees know not to do that that is very strange. If I would be Boeing managment then this would be a place where I would instill confidence in Boeing engineers by putting out some statement that tells the world that Boeing knows what they are doing although there is no law or other requirement to do so. It would just benefit Boeing to do so.


Sigh.

Statements like root cause investigation is 100% the norm for a situation like this. Literally the first thing out of any managers mouth. FAA and Boeing folks have already stated that retesting is not necessary. A RCCA would take place to make sure there wasn't an anomaly in the testing. Maybe a hydraulic cylinder over pressurized unexpectedly. Any number of things. Just to be sure that the conditions present in the test were actually what was intended. Then when you verify there wasn't an external anomaly that caused the failure you go in and fix the problem and correlate the change in FEMs using the test results. This is standard OP.

Your post is really just highly speculative. They were within 1% on one of the most complex tests you can perform. That's pretty freaking good. Nothing nefarious here folks. This literally happens all the time.
 
oschkosch
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 5:07 pm

kalvado wrote:
oschkosch wrote:
Does anyone know why they sort of "hid" the major fuselage damage?

Because general public can get (and actually gets) agitated over this stuff. Boeing has enough problems to handle; this is not the biggest one. It will be resolved to the satisfaction of engineering experts at Boeing, faa and customer airlines. That is honestly the end of story: some delay and resolved problem.
Boeing is not known for the openness, and being in a spotlight doesn't encourage being more open
but doesn't the public get more agitated and nervous when things that sound so bad like this get hidden and then leaked much later on, as in this example?

Gesendet von meinem SM-G950F mit Tapatalk
 
d8s
Posts: 121
Joined: Thu Feb 23, 2012 6:45 pm

Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sat Nov 30, 2019 5:08 pm

ikramerica wrote:
d8s wrote:
morrisond wrote:
Yes they are expected to fail - I think the bigger part of the story will be Boeing downplaying the story.

Pictures https://www.seattletimes.com/business/b ... uffer_tw_m


Really? "the test failed so explosively at just 1% shy of meeting federal requirements". What is there to cover up?

Probably left a few Home Depot fasteners in place by mistake...


I was going to say they bought the fasteners at Big Lots...
 
Ertro
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 5:17 pm

trpmb6 wrote:
Statements like root cause investigation is 100% the norm for a situation like this.


No they are not. Similar test are done on every new plane type and you don't find any other case when this kind of statement was made.

trpmb6 wrote:
Literally the first thing out of any managers mouth.


Maybe. This was a press release. Not internal discussions.

trpmb6 wrote:
FAA and Boeing folks have already stated that retesting is not necessary.


And EASA has indicated very soon after the photos were unearthed that they want to do their own assessment of the situation.
The extremely quick statement that retest is not necessary is not the one that instills confidence. Quite the contrary.

trpmb6 wrote:
Maybe a hydraulic cylinder over pressurized unexpectedly. Any number of things. Just to be sure that the conditions present in the test were actually what was intended. Then when you verify there wasn't an external anomaly that caused the failure you go in and fix the problem and correlate the change in FEMs using the test results. This is standard OP.


Yes. And after that is done then somebody can decide whether a retest is necessary.

trpmb6 wrote:
They were within 1% on one of the most complex tests you can perform


This complexity is also the worrying bit. Normally it is the wingspar that snaps so a much simpler thing. It is easy to believe that such much more simple thing can be calculated and designed to fail.

Now I am not sure and stressing the complexity of the situation is not going to make it easier to believe that everything is under control.
 
kalvado
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 5:28 pm

oschkosch wrote:
kalvado wrote:
oschkosch wrote:
Does anyone know why they sort of "hid" the major fuselage damage?

Because general public can get (and actually gets) agitated over this stuff. Boeing has enough problems to handle; this is not the biggest one. It will be resolved to the satisfaction of engineering experts at Boeing, faa and customer airlines. That is honestly the end of story: some delay and resolved problem.
Boeing is not known for the openness, and being in a spotlight doesn't encourage being more open
but doesn't the public get more agitated and nervous when things that sound so bad like this get hidden and then leaked much later on, as in this example?

Gesendet von meinem SM-G950F mit Tapatalk

It is one of several possible ways of thinking and looks like Boeing is adamant on keeping things that way.
Many other industries recognized that there is a lot of knowledge spread out among the general public, and being more open doesn't hurt as much. From car crash testing to all IT technical details published to pretty full information about medical problems - including patient discussion.
Possibly working in business-to-business environment means Boeing sees only that much value in public engagement. Maybe they think any trouble report would affect stock value which they value above all.
End result is that given Boeing has a less than stellar recent record in being on top of things (to put it mildly), and apparent decay of professionalism among broader industry - it is their choice to do so; it is my choice to be cautiosly sceptical about their product. They get my dollars in a pretty inderect way, and they care only that much about what I think.

FOr this particular case, a press release with sompe pictures or video saying "Yes, it looks bad - but think about it as a crash test..." - instead of getting a late leak - would defuse a lot of concerns. But maybe it is just me thinking so.
 
Waterbomber2
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 5:37 pm

If no additional testing is necessary, why did they SUSPEND the particular testing?
Was this the final test item or were there other tests that still needes to be performed when the thing went caboom unexpectedly?

Sure this particular area failed at 149% ultimate load, but ultimate load testing is not one test and you're done, it's several tests where you strain the wings and fuselage in many different positions.

If they had to suspend testing, it means to me that not all boxes were ticked yet.
How can you tick the remaining boxes with a fuselage that's cracked open and probable test infrastructure damage?

If you put out a statement like that, you need to follow-up and tell the full extent of the issue and the next step in the process, timelines, etc... If there is no issue, you don't put out a statement like that.
 
Sokes
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 6:14 pm

I assume for a long range plane Boeing doesn't want to carry around unnecessary 2% extra structure. That the failure appeared at 99% of design load speaks for Boeing's engineering department. Better to have it failed once and have an optimum design than to carry around unnecessary weight.
I'm impressed. So there is some hope for Boeing after all.
How is the management going to use such skill next? B767 Max?
Why can't the world be a little bit more autistic?
 
kalvado
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 7:44 pm

Sokes wrote:
I assume for a long range plane Boeing doesn't want to carry around unnecessary 2% extra structure. That the failure appeared at 99% of design load speaks for Boeing's engineering department. Better to have it failed once and have an optimum design than to carry around unnecessary weight.
I'm impressed. So there is some hope for Boeing after all.
How is the management going to use such skill next? B767 Max?

If you think about it, the first flight of 777X had been scheduled for April 2019. Part of that delay is on engines - although people say engines are fixed and re-delivered. Now there is a rework to be done on already produced frames - possibly adding weight above what would be saved on the refined design. And yet more time would be needed before delivery to compensate for that.
Now would that be penny wise overall?
And this is unlikely to translate into 1% weight difference. A380 wing was reinforced with some really trivial extra weight, few pounds if my memory serves me right, after missing the target by wooping 3%. With all the costs listed above on top of that. I suspect the same would be true for 777X - fix would include 3 screws and a roll of duck tape.
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure

Sat Nov 30, 2019 9:32 pm

Ertro wrote:
trpmb6 wrote:
Statements like root cause investigation is 100% the norm for a situation like this.


No they are not. Similar test are done on every new plane type and you don't find any other case when this kind of statement was made.

trpmb6 wrote:
Literally the first thing out of any managers mouth.


Maybe. This was a press release. Not internal discussions.

trpmb6 wrote:
FAA and Boeing folks have already stated that retesting is not necessary.


And EASA has indicated very soon after the photos were unearthed that they want to do their own assessment of the situation.
The extremely quick statement that retest is not necessary is not the one that instills confidence. Quite the contrary.

trpmb6 wrote:
Maybe a hydraulic cylinder over pressurized unexpectedly. Any number of things. Just to be sure that the conditions present in the test were actually what was intended. Then when you verify there wasn't an external anomaly that caused the failure you go in and fix the problem and correlate the change in FEMs using the test results. This is standard OP.


Yes. And after that is done then somebody can decide whether a retest is necessary.

trpmb6 wrote:
They were within 1% on one of the most complex tests you can perform


This complexity is also the worrying bit. Normally it is the wingspar that snaps so a much simpler thing. It is easy to believe that such much more simple thing can be calculated and designed to fail.

Now I am not sure and stressing the complexity of the situation is not going to make it easier to believe that everything is under control.


And this is why I am deciding it is futile to engage this community anymore. I am literally involved in testing aircraft, designing them, providing cert analysis and RCCA reports. But somehow I don't know how this works. I guess I should just shut my freaking mouth and let you all live in your ignorance. Damned if I do, damned if I don't. If you don't want to believe what I tell you, then by all means, continue to live on in your ignorance.

So done with this forum.
 
maint123
Posts: 255
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 12:59 am

trpmb6 wrote:
Ertro wrote:
trpmb6 wrote:
Statements like root cause investigation is 100% the norm for a situation like this.


No they are not. Similar test are done on every new plane type and you don't find any other case when this kind of statement was made.

trpmb6 wrote:
Literally the first thing out of any managers mouth.


Maybe. This was a press release. Not internal discussions.

trpmb6 wrote:
FAA and Boeing folks have already stated that retesting is not necessary.


And EASA has indicated very soon after the photos were unearthed that they want to do their own assessment of the situation.
The extremely quick statement that retest is not necessary is not the one that instills confidence. Quite the contrary.

trpmb6 wrote:
Maybe a hydraulic cylinder over pressurized unexpectedly. Any number of things. Just to be sure that the conditions present in the test were actually what was intended. Then when you verify there wasn't an external anomaly that caused the failure you go in and fix the problem and correlate the change in FEMs using the test results. This is standard OP.


Yes. And after that is done then somebody can decide whether a retest is necessary.

trpmb6 wrote:
They were within 1% on one of the most complex tests you can perform


This complexity is also the worrying bit. Normally it is the wingspar that snaps so a much simpler thing. It is easy to believe that such much more simple thing can be calculated and designed to fail.

Now I am not sure and stressing the complexity of the situation is not going to make it easier to believe that everything is under control.


And this is why I am deciding it is futile to engage this community anymore. I am literally involved in testing aircraft, designing them, providing cert analysis and RCCA reports. But somehow I don't know how this works. I guess I should just shut my freaking mouth and let you all live in your ignorance. Damned if I do, damned if I don't. If you don't want to believe what I tell you, then by all means, continue to live on in your ignorance.

So done with this forum.

We do testing on non aviation equipment. Our thumb rule, not always, is test at 150% of working load or pressure. But the equipment is expected to pass at 150 % test load or pressure. Test load is not the ultimate load.
 
justloveplanes
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sun Dec 01, 2019 1:39 am

zeke wrote:
trpmb6 wrote:
Let me say this plainly, had they done the exact same scenario but only gone to 8psi it would not have failed. That's because you have to consider the full state of stress, not just the compression caused by the down bend of the fuselage. You have to note that it's also an elevated hoop tension stress.


I understand that it’s a combined loads case, I said as much above. If it had just been wing bending or pressurisation it would not have failed, it failed with the combined loads.

trpmb6 wrote:
Lastly let me just state that buckling is a stability failure but not a structural failure. Even with permanent deformation you should still remain pressurized. You'd just have wrinkles in the skins.


That does not look like a buckling failure to me, it looks like it failed on the fasteners. The term I think you should be using is post buckling, not buckling.



Hmmm... Fasteners, eh? It could be a manufacturing vs. design problem. Boeing backed off its riveting robots on this program after this incident..... Curious....
 
GoSharks
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 2:20 am

maint123 wrote:
trpmb6 wrote:
Ertro wrote:

No they are not. Similar test are done on every new plane type and you don't find any other case when this kind of statement was made.



Maybe. This was a press release. Not internal discussions.



And EASA has indicated very soon after the photos were unearthed that they want to do their own assessment of the situation.
The extremely quick statement that retest is not necessary is not the one that instills confidence. Quite the contrary.



Yes. And after that is done then somebody can decide whether a retest is necessary.



This complexity is also the worrying bit. Normally it is the wingspar that snaps so a much simpler thing. It is easy to believe that such much more simple thing can be calculated and designed to fail.

Now I am not sure and stressing the complexity of the situation is not going to make it easier to believe that everything is under control.


And this is why I am deciding it is futile to engage this community anymore. I am literally involved in testing aircraft, designing them, providing cert analysis and RCCA reports. But somehow I don't know how this works. I guess I should just shut my freaking mouth and let you all live in your ignorance. Damned if I do, damned if I don't. If you don't want to believe what I tell you, then by all means, continue to live on in your ignorance.

So done with this forum.

We do testing on non aviation equipment. Our thumb rule, not always, is test at 150% of working load or pressure. But the equipment is expected to pass at 150 % test load or pressure. Test load is not the ultimate load.

What does your non-aviation equipment testing have to do with aviation this test, where to my understanding, the expected ultimate failure load is at 150%?
 
Sokes
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 3:15 am

trpmb6 wrote:

I guess I should just shut my freaking mouth and let you all live in your ignorance. Damned if I do, damned if I don't. If you don't want to believe what I tell you, then by all means, continue to live on in your ignorance.

So done with this forum.


"Either-Or":
https://www.youtube.com/watch?v=D9JCwkx558o
Why can't the world be a little bit more autistic?
 
maint123
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 4:44 am

GoSharks wrote:
maint123 wrote:
trpmb6 wrote:

And this is why I am deciding it is futile to engage this community anymore. I am literally involved in testing aircraft, designing them, providing cert analysis and RCCA reports. But somehow I don't know how this works. I guess I should just shut my freaking mouth and let you all live in your ignorance. Damned if I do, damned if I don't. If you don't want to believe what I tell you, then by all means, continue to live on in your ignorance.

So done with this forum.

We do testing on non aviation equipment. Our thumb rule, not always, is test at 150% of working load or pressure. But the equipment is expected to pass at 150 % test load or pressure. Test load is not the ultimate load.

What does your non-aviation equipment testing have to do with aviation this test, where to my understanding, the expected ultimate failure load is at 150%?

You do realize equipment is expected to PASS at test loads not FAIL, like in this case. And this is what is called a catastrophic failure, not just a crack.
 
GoSharks
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 5:24 am

maint123 wrote:
GoSharks wrote:
maint123 wrote:
We do testing on non aviation equipment. Our thumb rule, not always, is test at 150% of working load or pressure. But the equipment is expected to pass at 150 % test load or pressure. Test load is not the ultimate load.

What does your non-aviation equipment testing have to do with aviation this test, where to my understanding, the expected ultimate failure load is at 150%?

You do realize equipment is expected to PASS at test loads not FAIL, like in this case. And this is what is called a catastrophic failure, not just a crack.

Boeing designed to their planes to fail at 150% (or slightly above to be completely correct), but they failed at 149%. What is your point?

Catastrophic failure doesn't sound abnormal to me. The ideal design has every stressed component failing at the ultimate target load, not just one or two.
 
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bikerthai
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 5:52 am

OK,

Just some basic info for some questions posed a few days back.

There was a talk about the load one would see in severe turbulence. From the design stand point, the max load for these type of turbulence would be considered limit load. Ultimate load is 150% limit.

There was also talk about this ultimate test is being done on a pristene airframe. While the frame has never flown and does not have fatigue cycles imparted on to it, it would have had damage deliberately cut into the frames to simulate a life time of crack growth.

If you look at the failure, it was away from the body joint. The body joint has very thick skin with thick splice frame. The stiffness of that joint seems to drive the buckling to the weaker portion of the monocoque.

Unlike the original 777 static test, the failure for this frame will be In the fuselage as the composite wing will deflect beyond the capability of the fuselage. Note that Boeing did not break the 787 wing.

I had a difficult time visualizing how extra pressure would affect buckling loads. Then I simplify the free body to a simple beam under compression load. If you add a distributed load along the beam, then the buckling strength would go down.

And no, even though I've been with the company for over 30years, they still don't tell me everything going on in buildings across town or across the country.
:old:

From a design stand point, it may be as simple as increasing the gauge of a few stiffeners at the bottom of the fuselage to make up for the 1% miss. The real time consuming work is going back to the calculation to make sure the same miscalculation was not done elsewhere as well.

bt
Intelligent seeks knowledge. Enlightened seeks wisdom.
 
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seahawk
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 8:33 am

trpmb6 wrote:
Ertro wrote:
trpmb6 wrote:
Still don't understand why you guys are hung up on the pressure thing. Or freaking out about being short 1 percent.

If they had gone over by one or two percent you'd be claiming they didn't save enough weight and thus it will impact the consumer in raised ticket prices due to extra fuel costs.

Absolutely nothing improper with what they've done here. And this load case they tested is extremely conservative. You keep talking about 150% of limit load but seem to forget the superposition of the cases they used should never happen.

I listed in a previous post why I think they tested this case. Still valid.


If Boeing would have calculated that this exact spot on the plane can fail in this specific way just above 150% and it failed at 149% then that would not be a problem. However this seems not to be the case.

Boeing statement talks about "an issue arose", "suspend testing", "root-cause assessment over the coming weeks".

Those quotes seem to suggest that this was unexpected and that Boeing does not know how it failed. If they do not know how it failed then they could not possibly have designed it to fail at 151%. If a wingspar snaps during this test at 149% then Boeing or Airbus are not going to put out a statement like Boeing did here. The statement is going to be "Test highly succesful. The wing snapped at 149% in exactly the way it was predicted to fail at 150% so pretty darn close. We just add a tiny bit of material and we are done". And everybody is happy. Boeing clearly knows what they are doing. Now the fact that it failed at 149% seems like just a random accident. Manufacturing some spot which Boeing does not know is the rootcause point of failure slightly differently could have made this spot fail at 110% load instead.

It seems Boeing still does not know how it failed. Highly knowledgeable Boeing employees are still going on wild tangents on messageboards speculating how it could have failed. If Boeing has any idea how it failed and management does not distribute this clear information inside Boeing so that employees know not to do that that is very strange. If I would be Boeing managment then this would be a place where I would instill confidence in Boeing engineers by putting out some statement that tells the world that Boeing knows what they are doing although there is no law or other requirement to do so. It would just benefit Boeing to do so.


Sigh.

Statements like root cause investigation is 100% the norm for a situation like this. Literally the first thing out of any managers mouth. FAA and Boeing folks have already stated that retesting is not necessary. A RCCA would take place to make sure there wasn't an anomaly in the testing. Maybe a hydraulic cylinder over pressurized unexpectedly. Any number of things. Just to be sure that the conditions present in the test were actually what was intended. Then when you verify there wasn't an external anomaly that caused the failure you go in and fix the problem and correlate the change in FEMs using the test results. This is standard OP.

Your post is really just highly speculative. They were within 1% on one of the most complex tests you can perform. That's pretty freaking good. Nothing nefarious here folks. This literally happens all the time.


Imho the FAA said nothing to the event. And as the failure at 1% off, confirms the digital model they are using, no retesting should be needed. That is all I can conclude from the information we have.
 
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Revelation
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 1:56 pm

crimsonchin wrote:
When a company is in the news having been recently accused of not being straightforward with a software that may have contributed to the deaths of 300+ passengers, everything about the company is news, unfairly or not. That's what is happening here.

At least you recognize the unfair side of the equation.

Way too much piling on happening on this forum these days, IMO.

Ertro wrote:
trpmb6 wrote:
Still don't understand why you guys are hung up on the pressure thing. Or freaking out about being short 1 percent.

If they had gone over by one or two percent you'd be claiming they didn't save enough weight and thus it will impact the consumer in raised ticket prices due to extra fuel costs.

Absolutely nothing improper with what they've done here. And this load case they tested is extremely conservative. You keep talking about 150% of limit load but seem to forget the superposition of the cases they used should never happen.

I listed in a previous post why I think they tested this case. Still valid.


If Boeing would have calculated that this exact spot on the plane can fail in this specific way just above 150% and it failed at 149% then that would not be a problem. However this seems not to be the case.

Boeing statement talks about "an issue arose", "suspend testing", "root-cause assessment over the coming weeks".

Those quotes seem to suggest that this was unexpected and that Boeing does not know how it failed. If they do not know how it failed then they could not possibly have designed it to fail at 151%. If a wingspar snaps during this test at 149% then Boeing or Airbus are not going to put out a statement like Boeing did here. The statement is going to be "Test highly succesful. The wing snapped at 149% in exactly the way it was predicted to fail at 150% so pretty darn close. We just add a tiny bit of material and we are done". And everybody is happy. Boeing clearly knows what they are doing. Now the fact that it failed at 149% seems like just a random accident. Manufacturing some spot which Boeing does not know is the rootcause point of failure slightly differently could have made this spot fail at 110% load instead.

It seems Boeing still does not know how it failed. Highly knowledgeable Boeing employees are still going on wild tangents on messageboards speculating how it could have failed. If Boeing has any idea how it failed and management does not distribute this clear information inside Boeing so that employees know not to do that that is very strange. If I would be Boeing managment then this would be a place where I would instill confidence in Boeing engineers by putting out some statement that tells the world that Boeing knows what they are doing although there is no law or other requirement to do so. It would just benefit Boeing to do so.

I think this would be getting next to no attention if it weren't for the MAX tragedy.

People should be able to step back and see it for what it is, but can't seem to resist their urge to give Boeing a kick while they are down.

In turn the media realizes people are up for it so they use the most sensational language they can to describe what is in fact a routine engineering test with an almost ideal outcome.

bikerthai wrote:
OK,

Just some basic info for some questions posed a few days back.

There was a talk about the load one would see in severe turbulence. From the design stand point, the max load for these type of turbulence would be considered limit load. Ultimate load is 150% limit.

There was also talk about this ultimate test is being done on a pristene airframe. While the frame has never flown and does not have fatigue cycles imparted on to it, it would have had damage deliberately cut into the frames to simulate a life time of crack growth.

If you look at the failure, it was away from the body joint. The body joint has very thick skin with thick splice frame. The stiffness of that joint seems to drive the buckling to the weaker portion of the monocoque.

Unlike the original 777 static test, the failure for this frame will be In the fuselage as the composite wing will deflect beyond the capability of the fuselage. Note that Boeing did not break the 787 wing.

I had a difficult time visualizing how extra pressure would affect buckling loads. Then I simplify the free body to a simple beam under compression load. If you add a distributed load along the beam, then the buckling strength would go down.

And no, even though I've been with the company for over 30years, they still don't tell me everything going on in buildings across town or across the country.
:old:

From a design stand point, it may be as simple as increasing the gauge of a few stiffeners at the bottom of the fuselage to make up for the 1% miss. The real time consuming work is going back to the calculation to make sure the same miscalculation was not done elsewhere as well.

bt

Thanks to you and trpmb6 for sharing your knowledge with the forum, I for one appreciate it.
Wake up to find out that you are the eyes of the world
The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own
 
JAAlbert
Posts: 1972
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Sun Dec 01, 2019 5:48 pm

d8s wrote:
trpmb6 wrote:
My goodness. This thread makes me want to quit engaging the airliners community. It's almost as bad as the non-av threads.

Where to begin. I have been involved in many tests like this one. This is hardly newsworthy. If only you had seen the things I've seen.

What do you expect us engineers to do? We design aircraft to meet a specific set of regulations and we push the design as far as possible to be the most efficient aircraft. You guys want cheaper tickets, more range using less fuel. Only way to do that is take the weight out. This is what you get. Mind you no aircraft in service would ever see this flight condition.

Boeing likely tested the frame to this condition to A) see what she could handle and B) help with production MRB, fleet repairs etc. We often will overload structure in a test for a couple reasons.. helps us justify repairs and defects etc. We actually will introduce failures into the structure to see what residual strength remains.

One thing folks also don't understand is we sometimes discover that to get a certain load level in one part of the fuselage you have to overload another area because of how our test cradles are set up. When in real life everything is a nice distributed load, the only way to test it without exorbitant costs is using cradles and wiffletrees that introduce point loads into the frame. This can lead to failures.

Fact is, this is a great test result. Sure they missed it by 1% but yall are extremely naive if you think that is catastrophic. Considering all the factors involved. Consider just some of the simplest points, someone developed the loads. Some margin of error there. Tolerance build up in the manufacturing process. Could be everything came in on the thin side. Maybe the stiffnesses in their FEMs was slightly off. The way the load is introduced to the test, as mentioned earlier, overloads local areas. We overload to account for thermal and environmental conditions. Remember CFRP wing with aluminum fuselage. Need to overload that to account for thermal mismatch.

That is why we test.

As for transparency, when I originally read the release about the failure it was clear to me they were discussing the cargo door surround structure. That's exactly what the pictures show. Don't blame Boeing, blame the folks who either misunderstood or simply don't know how this works.

Kudos to the Boeing engineers working this, they executed an excellent test. Hats off to you.

To the rest of you armchair engineers, I won't criticize you for how you do your job, don't criticize us until you go and get the degree and do the job we do. We keep you safe, a little respect would be nice.

Parting gift: almost certain the FAA would have had representatives present for the test. So any talk of a coverup is simply fearmongering/conspiracy peddling nonesense.



Not just today, but everyday, I am thankful for the engineers who designed these machines! Thanks for setting the stupidity record of this website straight!


I second the sentiment! trpmb6 don't withdraw from the conversations! I have no experience or training in any aspect of aircraft design, testing or flying (lots as an economy class passenger tho!) and what I love about A.net are the professionals who do have this experience discussing their expertise. I love commercial aviation and reading about the science behind how these beasts are designed, built and flown. I admit, I don't understand a lot of what I read, but I do pick up enough knowledge to have a better idea of how and why things are done a certain way. I don't mind the conspiracy theorists or the shoot-first-learn-the-facts-later folks online, just as long as they allow the fact-holders to correct the sometimes crazy claims and ideas.

As an outside enthusiast, news of the the door blowing out interested me, but did not alarm me. It happened just below the targeted maximum and it happened right when it should have - during a test. That Boeing did not provide more details to the public as to the exact details of the failure also doesn't concern me -- I, your average reader, would have no knowledge to asses that information. Had Boeing kept the information from the regulatory authorities, I would be very concerned. Here it seems everyone who needed to know about this event received all the information necessary to evaluate and correct the error. Interesting news tidbit and love reading about the testing process. Otherwise, time to move on.

I cannot wait to see the 777-9 in the air!
 
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kanban
Posts: 3984
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Re: Pictures surfacing of 777X Sept Test Failure

Sun Dec 01, 2019 6:02 pm

one thing a lot of people fail to realize is the fatigue tests start at 1% and are gradually ramped up to destruction. The 150% is an arbitrary figure, had they reached it the next goal would have been 160% in 1% increments. Also the fatigue test airframe is always destroyed after testing.

about the failure points on this test, I speculate that at the crack initiation point there may have been a crack caused by the robotic riveters.. maybe a drilling burr left in place or an oversize fastener from a robotic oops that as repaired. we probably will never know however the sudden axing of the robotic riveters after this test is interesting. if the cause was a manufacturing process error, steps will be taken.
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure

Mon Dec 02, 2019 1:18 am

kanban wrote:
one thing a lot of people fail to realize is the fatigue tests start at 1% and are gradually ramped up to destruction. The 150% is an arbitrary figure, had they reached it the next goal would have been 160% in 1% increments. Also the fatigue test airframe is always destroyed after testing.

about the failure points on this test, I speculate that at the crack initiation point there may have been a crack caused by the robotic riveters.. maybe a drilling burr left in place or an oversize fastener from a robotic oops that as repaired. we probably will never know however the sudden axing of the robotic riveters after this test is interesting. if the cause was a manufacturing process error, steps will be taken.


Robotic riveters is not the issue. A large portion of the 737 is autoriveted.

This wasn't a fatigue test either.
 
9Patch
Posts: 405
Joined: Wed Mar 13, 2019 10:38 pm

Re: Pictures surfacing of 777X Sept Test Failure

Mon Dec 02, 2019 1:38 am

trpmb6 wrote:
Robotic riveters is not the issue. A large portion of the 737 is autoriveted.

This wasn't a fatigue test either.


I'm glad you're still posting.
 
peterinlisbon
Posts: 1579
Joined: Wed Feb 01, 2006 3:37 am

Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Mon Dec 02, 2019 2:51 am

morrisond wrote:
Cool you can pull 3.74G's in the 777X before the frame fails!


That sounds wonderful until you fly through a thunderstorm and you start to see the wings bending.
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure

Mon Dec 02, 2019 3:16 am

9Patch wrote:
trpmb6 wrote:
Robotic riveters is not the issue. A large portion of the 737 is autoriveted.

This wasn't a fatigue test either.


I'm glad you're still posting.


It's an addiction.
 
JayinKitsap
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Joined: Sat Nov 26, 2005 9:55 am

Re: Pictures surfacing of 777X Sept Test Failure

Mon Dec 02, 2019 4:58 am

This static test frame had been undergoing tests since 2018. Its most important thing is to validate the FEM model of the aircraft. Thousands of strain gauges around the aircraft, deflections measured, every load cylinder tested, then various load conditions tested. To prove the FEM, it needs to be within say 1% of test data, if wider added margin needs to be applied to cover the inaccuracy.

Some of the ultimate loads tests could have occurred, for example, the hull pressurization to 150% is likely to have happened prior to this final test. It is known that it was on its last test when this occurred, because is sure to be damaged in this test. Once damaged, nearly all testing is risky as every part could be compromised, causing a low failure in the follow on test.

So yes, once the rupture occurred the test stopped, the anchoring of the tail area to the foundation resists the wing uplift thru the rear fuse, which is broken.


https://www.boeing.com/company/about-bc ... 11-18.page

https://lessonslearned.faa.gov/Northwes ... pop_up.htm

https://www.aa.washington.edu/files/mae ... 3-2014.pdf
 
gcb5196
Posts: 56
Joined: Fri Aug 12, 2011 6:45 pm

Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Mon Dec 02, 2019 6:04 am

trpmb6 wrote:
My goodness. This thread makes me want to quit engaging the airliners community. It's almost as bad as the non-av threads.

Where to begin. I have been involved in many tests like this one. This is hardly newsworthy. If only you had seen the things I've seen.

What do you expect us engineers to do? We design aircraft to meet a specific set of regulations and we push the design as far as possible to be the most efficient aircraft. You guys want cheaper tickets, more range using less fuel. Only way to do that is take the weight out. This is what you get. Mind you no aircraft in service would ever see this flight condition.

Boeing likely tested the frame to this condition to A) see what she could handle and B) help with production MRB, fleet repairs etc. We often will overload structure in a test for a couple reasons.. helps us justify repairs and defects etc. We actually will introduce failures into the structure to see what residual strength remains.

One thing folks also don't understand is we sometimes discover that to get a certain load level in one part of the fuselage you have to overload another area because of how our test cradles are set up. When in real life everything is a nice distributed load, the only way to test it without exorbitant costs is using cradles and wiffletrees that introduce point loads into the frame. This can lead to failures.

Fact is, this is a great test result. Sure they missed it by 1% but yall are extremely naive if you think that is catastrophic. Considering all the factors involved. Consider just some of the simplest points, someone developed the loads. Some margin of error there. Tolerance build up in the manufacturing process. Could be everything came in on the thin side. Maybe the stiffnesses in their FEMs was slightly off. The way the load is introduced to the test, as mentioned earlier, overloads local areas. We overload to account for thermal and environmental conditions. Remember CFRP wing with aluminum fuselage. Need to overload that to account for thermal mismatch.

That is why we test.

As for transparency, when I originally read the release about the failure it was clear to me they were discussing the cargo door surround structure. That's exactly what the pictures show. Don't blame Boeing, blame the folks who either misunderstood or simply don't know how this works.

Kudos to the Boeing engineers working this, they executed an excellent test. Hats off to you.

To the rest of you armchair engineers, I won't criticize you for how you do your job, don't criticize us until you go and get the degree and do the job we do. We keep you safe, a little respect would be nice.

Parting gift: almost certain the FAA would have had representatives present for the test. So any talk of a coverup is simply fearmongering/conspiracy peddling nonesense.


Well said and thank you. Okay, from the FARs, "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)." FAR 25.301. What is the factor of safety? "Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure." FAR 25.303. So, the limit load is the maximum load to be expected in service and the safety factor is 1.5 times that. This and many other tests are designed to see that safety factor. The idea that this failure at 149% means that during turbulence the plane is somehow unsafe is absurd. Read the FARs. Maximum loads expected in service is 100%, that's turbulence, higher than normal g's, a higher gust of wind, a hard landing, bird crap on the window, maybe the sun hitting the fuselage at a weird angle. I don't know what the maximum expected loads are, but someone does and they have worked so far. The extra 50% is on top of all that, in addition to, 1.5 times. 1 is normal up to and including the O.S! moments, the .5 is so they can all live to tell about it. All transport category aircraft are certified at that. If you aren't comfortable with that then I don't suggest flying on any aircraft.
Also, to further my point, this is one test frame that this is performed on. There are variations in manufacturing and materials. This one frame stands in for and behalf of every plane that comes after it. The 1.5 safety factor covers most of those variations including fatigue. One plane may be stronger and one inherently weaker. Every plane that takes to the sky is not tested to ultimate failure because of that safety factor. It is factored in all the planes from every transport category aircraft manufacturer. If you are uneasy about flying on a Boeing 777X because it passed it's limit load test exceptionally well but barely failed the ultimate load test I wouldn't recommend flying on any other aircraft. If it had failed at 99% I would be concerned, the fact that it failed so close to the 1.5 safety margin means it's safe, just not certifiably safe, yet. And in praise to the engineers, it was almost perfect. Same kudos to engineers at all manufacturers who get it almost there, don't want to be seen as a fanboy. By the way if given the opportunity to fly on an A380 I would, wing spar cracks and all.

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