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dragon6172
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 2:35 am

Waterbomber2 wrote:
dragon6172 wrote:
Waterbomber2 wrote:
The concern is not whether or not it failed within certification tolerances.
The concern is that it failed at an unexpected point of failure and in a catastrophic way.

You dont know that it is an unexpected point of failure. It is possible that this failure came at the location expected to fail first. And the failure certainly would expected to be catastrophic in this sort of test.

The only thing known is that it failed at a lower level of stress than forecasted.


I know it because Boeing said it: "an issue occurred that required the team to suspend testing" . Translated: we didn't expect that to happen.

Exactly, you know that Boeing said the test failed unexpectedly. You dont know if it failed at an unexpected location, which is what you imply in your original post.
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par13del
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 2:50 am

rbavfan wrote:
Because failing like this 1% below the required FAA limits means you failed the test. Failing should mean it does not get it's cert till the upgrade is fully tested and passes above the requirement line, not below it.

Need to get the MAX FAA then because the 777X FAA initial thought is that because the failure was at 1% below once root analysis is done they should be able to show passage of the test by analysis once updates are completed....shows how much the FAA knows.
 
acechip
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 3:48 am

Post the Max debacle, the whole aspect of "meeting FAA requirements" is entirely up to interpretation. I think its time that manufacturers start to 'over engineer airplanes once again. I dont mind spending a few tens of $$ for this if the planes have to be safe as a vault. This computer aided, optimised , cost saving engineering is the root cause behind so many design issues these days. I know this is a bit of a sweeping statement, but its more or less the truth.
 
RickNRoll
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:12 am

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
Did you expect them to upplay it? I would to see the pictures but Boeing could have the whole matter under control once they get to the root cause and rectify it.
 
JayinKitsap
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:20 am

keesje wrote:
.
I was told it was just a cargo door latch, A380 had something similar & there are no indications program could be delayed.

:covereyes:

Image

Are we serious ?! Airframe write-off. No wonder it became so quiet & everybody was looking the other way.

Everything is just fine, nothing to see here.... I recommend a solid root cause analyses, by FAA & JATR.

Hopefully it has nothing to do with overly aggressive Grandfathering of 77W Design & Requirements. I give it 50% chance.


Yes, everything is just fine, seems to be a normal test in a field where weight savings is critical, they are not overdesigned, but a 1.5 FOS is a healthy safety factor, we certainly do not need 1.6. Concrete buildings are designed at 1.4 on dead load, and 1.0 on seismic load - no worries mate.

This was a destructive test, no repeats should be done because the second time to these levels it will be below. Just like the test is to prove for 3 seconds - it made it, but a lot of articles would likely fail if the test was held for an hour, still more at a day, etc.

The original 777 load test the wing ruptured at 154%, in the attached video of the original test one notes that the wing basically shattered everywhere at once on both sides of the plane, note earlier in the test the massive ripples in the fuselage. In such a load test one takes the maximum condition of each loading in what would be called the envelope solution. The 77W fuse was designed for 8,000 elevation cabin pressure, the 77X is going for 6,000 elevation cabin pressure. The selected cabin pressure would be for the highest flight line less the relieve valve overage, probably set at 5,500 elevation. 10 PSI is just under 2/3 bar, so around 1/2 bar envelope design pressure. But this cabin pressure would be far lower if at 30,000', where this max load of pulling out of a screaming dive from 40,000 at mach 1 into the eyewall of Hurricane Maria. At that location and the way it burst it is very likely analysis at that frame where the failure occurred would meet 1.50 if the cabin pressure was 4% less, which is likely where the envelope is, or at the worst the cabin pressure is set at 6,200 feet not 6,000.

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

Testing pressure vessels with air is quite dangerous, air expands rapidly causing shell fractures to zipper like crazy. Although cryogenic fluids involved this space-X failed pneumatically not hydrostatically. The rush of gas launched the top out of the park.

https://www.youtube.com/watch?v=NFz96sB0KqI
 
426Shadow
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 5:10 am

rbavfan wrote:
TTailedTiger wrote:
What exactly do you want Boeing to say? Do you think any company is going to trash talk their own product? Neither Boeing or Airbus (or any other aircraft manufacturer) even take swipes at each other. It was a stress test and and it did exactly what it was intended to do. Find the weak points. If you can do better and promise a flawless result the first time then I'm sure they'd love to hear from you.


The point is not that it failed at 1% below the required limit. Those things are fixed & retested. The point is rather than state if failed and they are going over the location and doing strengthening. But rather that they said a door blew off. Also note in the story about how they are looking at not having to repeat the test. NO you should do the test again on the strengthened frame and make sure it passes the FAA min. Then go from there. Thats what Boeing used to do when they were only Boeing and before the stock market played how many deaths can we withstand if it happens to fail. My veiw of that is those that care more about pure profit than how many could die should have their relatives die in the crash, "if it happens"

I want the old Boeing back, Safety before share value! Because safety builds share value.


So you just going to ignore the part where the Seattle times admitted they all got the story wrong? Let me guess, it doesn't fit your narrative.
We are all just fanboys, our opinions don't make or break businesses.
 
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seahawk
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 5:56 am

BaconButty wrote:
The A380 wing failure is an interesting one. One of the programme guys came out and said it was due to a late MTOW increase - this was widely ridiculed here, as much like their counterparts in Chicago now, they were at a the nadir of their credibility. Turned out to be true, it was the 569T option available from launch, presumably because early frames were 6T overweight. So basically the wing test failed at 147% of ultimate load iirc, but it was actually pretty close to what was presumably required for a 560T mtow aircraft. They were quick off the mark with the fix too, so were probably expecting it.

Idle speculation but I wonder if something similar is happening on the 77X? It could be bad news if there's an MTOW increase to compensate for being overweight, good news if they found margins elsewhere and made a late decision to add capability. Are the fuselage stress tests dependent on MTOW to the extent the wing tests are? Or are pressurisation loads the key driver?


Airbus was expecting it. The stronger replacement parts were already designed. It was a MTOW increase in combination with some too aggressive attempt to reduce the weight of the plane and it was limited in location and affected structural components.

From the photo of the 777 I would not want to make any assessment on the severity of the problem. My first impression was that there was also damage to the internal load bearing structure and not only to the outer shell.
 
sciing
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 6:21 am

Strato2 wrote:
BlatantEcho wrote:
So there was a failure 3x at what is ever expected in the most extreme real life situation ever.

Why is this stuff news?


Because the failure was catastrophic and not just door blowing off?


Respect, you see on that picture the origin of the defect?
From where do you know where it started.
The disintegration of larger part is quite logical as the structure could not stop propagation of the resulting cracks! So a small weakpoint end in much larger event especially at overload.
It is really amazing how total laymen to the topic ejaculate there same nonsens in the forums.
I am for sure not an Boeing fan but what makes me really worry is when stupid idiots try to involve in processes there they have absolutely no glue!
 
sciing
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 6:29 am

Baldr wrote:
Polot wrote:
Baldr wrote:
Also, is this the first time that wings being tested at ultimate load (1.5 times the limit load) has resulted in the rupture of the fuselage instead of the wings themselves?

This is not the wing load test you are thinking of.


Which test am I thinking of then?

The test wing of the 777-200 failed at 154% of limit load; the test wing of the C-5A failed at 125% of limit load, while the test wing of the A380 failed at 146% of limit load -- no massive fuselage ruptures occurred.

Again, this was not a wing load test, but fuselage pressurization test.
 
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seahawk
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 6:35 am

sciing wrote:
Baldr wrote:
Polot wrote:
This is not the wing load test you are thinking of.


Which test am I thinking of then?

The test wing of the 777-200 failed at 154% of limit load; the test wing of the C-5A failed at 125% of limit load, while the test wing of the A380 failed at 146% of limit load -- no massive fuselage ruptures occurred.

Again, this was not a wing load test, but fuselage pressurization test.


And it was the final destruction test after certification was achieved.
 
alyusuph
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 6:43 am

MoKa777 wrote:
If the failure occurred at a lower percentage of the ultimate load, then maybe this story would be something to be concerned about. However, according to the article, this failure occurred at 99% of the load limit they test (1.48x of 1.5x).

The relatively good news for Boeing is that because the test failed so explosively at just 1% shy of meeting federal requirements, it will almost certainly not have to do a retest. Regulators will likely allow it to prove by analysis that it’s enough to reinforce the fuselage in the localized area where it failed.
I am not an Airbus or Boeing fan, just an aircraft fan
 
downdata
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 6:59 am

BlatantEcho wrote:
So there was a failure 3x at what is ever expected in the most extreme real life situation ever.

Why is this stuff news?


Thats not really true. Severe turbulence experienced by airliners are between 2 - 2.5G according to Boeing (Such as one 2.5G turbulence encountered by TWA374). It is still well below the design limit of 3.75G but 1.3G is hardly the “most extreme real life situation ever.”
 
Waterbomber2
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 6:59 am

seahawk wrote:
sciing wrote:
Baldr wrote:

Which test am I thinking of then?

The test wing of the 777-200 failed at 154% of limit load; the test wing of the C-5A failed at 125% of limit load, while the test wing of the A380 failed at 146% of limit load -- no massive fuselage ruptures occurred.

Again, this was not a wing load test, but fuselage pressurization test.


And it was the final destruction test after certification was achieved.


This is called ultimate load testing.

Here is the video of the A350 swaying its wings like a bird, and the Airbus spokesperson says: "if ever a cargo door is opening, we can damage the complete (test facility) building to detrimental effect".

https://youtu.be/B74_w3Ar9nI
 
art
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 7:15 am

IIRC after the A380 wing failed below the 150% threshold the problem was quickly rectified at a cost of an additional 25Kg to the wing's weight.

Anything more concerning about this stress test result?
 
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LAX772LR
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 7:22 am

TTailedTiger wrote:
I didn't know Boeing or any other company had any obligations to answer to the public.

If the issue at hand involves or could be tied to a fiduciary duty, then Boeing has an obligation to inform/"answer to" its shareholders.... who may as well be "the public"
I myself, suspect a more prosaic motive... ~Thranduil
 
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 7:33 am

Polot wrote:
Boeing never said the door blew off. Please provide the quote where Boeing said the door flew off.


But that is the issue, many media sources had done the right thing and contacted Boeing for comment/statement regarding the matter, and a Boeing given the opportunity neither confirmed or denied a door blew off. They just gave a lame statement saying something happened which interrupted testing, which gives the impression testing will resume.

Can I also help people understand when a significant failure like this happens after the explosive depressurization of the lower deck, it can result in a failure of other components as the floor is not designed to carry a 10 psi load from a pressurized upper deck and depressurization in the lower deck. One the side of the cabin wall there should be vents to allow air to move from the upper deck to the lower deck without failing the floor.

This is not an interruption of testing, the significant failure is the end of that static airframe. The only way to resume the same testing would be to start again with another static frame which will not happen, and would not be necessary.

Boeing could simply decide not to change any of the structure and just reduce the maximum cabin diff a little and/or maximum cruise altitude, it would only mean a small increase the cabin altitude. By far the simplest way to move forward.

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.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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seahawk
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 7:56 am

Waterbomber2 wrote:
seahawk wrote:
sciing wrote:
Again, this was not a wing load test, but fuselage pressurization test.


And it was the final destruction test after certification was achieved.


This is called ultimate load testing.

Here is the video of the A350 swaying its wings like a bird, and the Airbus spokesperson says: "if ever a cargo door is opening, we can damage the complete (test facility) building to detrimental effect".

https://youtu.be/B74_w3Ar9nI


You are right, I translated directly from German in my head. But the meaning is the same.
 
Waterbomber2
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 7:59 am

zeke wrote:
Polot wrote:
Boeing never said the door blew off. Please provide the quote where Boeing said the door flew off.


But that is the issue, many media sources had done the right thing and contacted Boeing for comment/statement regarding the matter, and a Boeing given the opportunity neither confirmed or denied a door blew off. They just gave a lame statement saying something happened which interrupted testing, which gives the impression testing will resume.

Can I also help people understand when a significant failure like this happens after the explosive depressurization of the lower deck, it can result in a failure of other components as the floor is not designed to carry a 10 psi load from a pressurized upper deck and depressurization in the lower deck. One the side of the cabin wall there should be vents to allow air to move from the upper deck to the lower deck without failing the floor.

This is not an interruption of testing, the significant failure is the end of that static airframe. The only way to resume the same testing would be to start again with another static frame which will not happen, and would not be necessary.

Boeing could simply decide not to change any of the structure and just reduce the maximum cabin diff a little and/or maximum cruise altitude, it would only mean a small increase the cabin altitude. By far the simplest way to move forward.

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.


For testing to resume, if more testing is needed but assuming it does given that it was suspended, they're going to need another airframe considering the extent of the damage, to repair the testing facilities if damaged, and to set it up for testing.

It could be weeks, months worth of delays.

Someone must have cast a powerful curse on Boeing, nothing is going right for them at the moment. If another ill-timed high profile accident happens anytime soon, it will be Boeing on the ultimate load test rig. The industry needs Boeing so fingers crossed that they can ride this out without too many more issues.
We need the real Boeing back, the engineering company that used to make the best aircraft in the world, not Boeing, the money hoarding machine.
 
Baldr
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 9:52 am

sciing wrote:
Baldr wrote:
Polot wrote:
This is not the wing load test you are thinking of.


Which test am I thinking of then?

The test wing of the 777-200 failed at 154% of limit load; the test wing of the C-5A failed at 125% of limit load, while the test wing of the A380 failed at 146% of limit load -- no massive fuselage ruptures occurred.

Again, this was not a wing load test, but fuselage pressurization test.


No, this was not just a pressurisation test. It was the ultimate wing bending test at limit load where the fuselage typically is pressurised to more than 1.3 Bar; or 18.85 PSI.

Here's the time point in the video -- link provided by Waterbomber2 -- that explains the set up of the A350 structural static testing (i.e. pressurisation, wing bending etc.)

http://www.youtube.com/watch?v=B74_w3Ar9nI&t=2m7s
 
Amiga500
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 10:21 am

Off the top of my head - "normal" operating envelope (limit load) => +3.0G / -1.0G

Ultimate limit load puts a factor of 1.5 on that.
 
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SheikhDjibouti
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 12:15 pm

Once again, Zeke nails it. :bigthumbsup:
zeke wrote:
Polot wrote:
Boeing never said the door blew off.

But that is the issue, many media sources had done the right thing and contacted Boeing for comment/statement regarding the matter, and a Boeing given the opportunity neither confirmed or denied a door blew off. They just gave a lame statement saying something happened which interrupted testing, which gives the impression testing will resume.

What Boeing Said:
https://boeing.mediaroom.com/news-relea ... tem=130500

Boeing Statement on 777X Load Testing
"CHICAGO, September 10, 2019 – During final load testing of the 777X static test airplane, a test which involves bending the wings of the airplane up to a level far beyond anything expected in commercial service, an issue arose that required the team to suspend testing. The testing issue occurred during the final minutes of the test, at approximately 99 percent of the final test loads, and involved a depressurization of the aft fuselage."

"During final testing...an issue arose"
"and involved a depressurization of the aft fuselage."
An issue arose? :rotfl: Just as it says in my sign-off; "Nothing to see here, please move along" Or not.... :roll:

Depressurization events occur on a regular (daily?) basis, and most of the time the oxygen masks drop and the aircraft descends rapidly before making a perfectly normal landing.
Does that tally with the pictures we see, and the description of the event from Boeing? :shakehead:

One would think they are describing a tiny pinhole in the skin, or the partial failure of a door seal.
But as several here have rushed to point out, Boeing didn't actually lie. No Sir!. No lies were told in the totally obsfucation of the truth today. :banghead:

zeke wrote:
The 777 currently has a maximum altitude of 43100 ft, which is a pressure of 2.34 psi in a standard atmosphere...
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.
{Brilliant explanation from Zeke; see original post for full transcript}

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.

:yes:

Playing devil's advocate (in this case the devil is a certain company headquartered in Chicago); if this was primarily a wing-bending stress test (@ 150%), then the depressurization was a secondary failure - still very important, but do the FAA also require this aspect to be at 150%? Maybe Boeing were doing nothing wrong in maintaining cabin pressure at normal levels? :scratchchin:

Either way, I don't see this event as a big engineering challenge for Boeing or the death of the 77X. The failure is not the problem. The cover-up is.
Nothing to see here; move along please.
 
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Polot
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 12:30 pm

The “cover up” is only a problem if they are lying to the FAA and other certifying authorities about the extent of the failure. The FAA is the one certifying the plane, not the media and public.

Trying to downplay the event (as all companies do) may not be the smartest PR move in the current climate, but Boeing technically does not owe us any explanation as to what happened. I think the main problem here is that many people are too impatient, want to play private investigator with the expectation that a company must tell them everything immediately, then get all upset when a company doesn’t indulge them.
 
justloveplanes
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 12:32 pm

[list=][/list]
btfarrwm wrote:
I hope aviation engineers can weigh in, but the keel of an airplane is one of the things that should never-ever fail. To be fair to Boeing, the article states they chose to stress the frame beyond what was required, (simultaneously stressing the wings and keel under high cabin pressure)...but the final analysis will be interesting. What are the FAA requirements for G-loading of the keel during non-normal operations?


They also ramped up cabin pressure to 10 psi.
 
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SheikhDjibouti
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 12:42 pm

justloveplanes wrote:
btfarrwm wrote:
I hope aviation engineers can weigh in, but the keel of an airplane is one of the things that should never-ever fail. To be fair to Boeing, the article states they chose to stress the frame beyond what was required, (simultaneously stressing the wings and keel under high cabin pressure)...but the final analysis will be interesting. What are the FAA requirements for G-loading of the keel during non-normal operations?

They also ramped up cabin pressure to 10 psi.

:rotfl:
Ramped up? That's the same differential you find flying at FL430 (see zeke's post)

But if you believe the test should only stress the wings as if the aircraft spends it's life at ground level, then yes, Boeing went beyond the minimum.
Nothing to see here; move along please.
 
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Polot
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 12:54 pm

zeke wrote:
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.

6% safety margin versus what? The frame wasn’t just undergoing pressurization. When flying at 43,000ft are aircraft routinely having their wings pushed up ~28 ft and fuselage ends pushed down with millions of lbs of force (from article)? We don’t even know if the pressurization was the cause of the failure, and in your calculations you are completely ignoring that the test has a safety margin built in.

To be frank, your “safety margin” number is completely irrelevant and not actually representative of what the real world safety margin would be. If they kept that pressurization and bent the wings and fuselage more to 150% stress and passed would you still be worried? After all that means they still only tested up to 150% of the expect load with a “6% safety margin” when it comes to pressurization.
 
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 1:37 pm

Polot wrote:
zeke wrote:
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.

6% safety margin versus what? The frame wasn’t just undergoing pressurization. When flying at 43,000ft are aircraft routinely having their wings pushed up ~28 ft and fuselage ends pushed down with millions of lbs of force (from article)? We don’t even know if the pressurization was the cause of the failure, and in your calculations you are completely ignoring that the test has a safety margin built in.

To be frank, your “safety margin” number is completely irrelevant and not actually representative of what the real world safety margin would be. If they kept that pressurization and bent the wings and fuselage more to 150% stress and passed would you still be worried? After all that means they still only tested up to 150% of the expect load with a “6% safety margin” when it comes to pressurization.


The test is representative of a pressurised aircraft flying through convective weather at maximum altitude. The way the aircraft will normally encounter loads of that nature are as a result of gusts.

The margin you are talking about is the wing bending moment. The margin I stated was is relation to maximum pressurisation differential.

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.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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Polot
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 1:58 pm

zeke wrote:
Polot wrote:
zeke wrote:
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.

6% safety margin versus what? The frame wasn’t just undergoing pressurization. When flying at 43,000ft are aircraft routinely having their wings pushed up ~28 ft and fuselage ends pushed down with millions of lbs of force (from article)? We don’t even know if the pressurization was the cause of the failure, and in your calculations you are completely ignoring that the test has a safety margin built in.

To be frank, your “safety margin” number is completely irrelevant and not actually representative of what the real world safety margin would be. If they kept that pressurization and bent the wings and fuselage more to 150% stress and passed would you still be worried? After all that means they still only tested up to 150% of the expect load with a “6% safety margin” when it comes to pressurization.


The test is representative of a pressurised aircraft flying through convective weather at maximum altitude. The way the aircraft will normally encounter loads of that nature are as a result of gusts.

The margin you are talking about is the wing bending moment. The margin I stated was is relation to maximum pressurisation differential.

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.


How often and strong are these gusts of wind that are increasing the pressurization load on the aircraft at maximum altitude?
 
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 2:23 pm

Polot wrote:
How often and strong are these gusts of wind that are increasing the pressurization load on the aircraft at maximum altitude?


All you need to do is fly though a thunderstorm in the tropics.
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Polot
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 2:48 pm

zeke wrote:
Polot wrote:
How often and strong are these gusts of wind that are increasing the pressurization load on the aircraft at maximum altitude?


All you need to do is fly though a thunderstorm in the tropics.

The tops of thunderstorms actually have higher pressure, it is at lower altitudes/sea level that the air pressure drops and where the meteorological measurements are being preformed.

This is also kind of ignoring how your altimeter is basically just a barometer calibrated to give you a height in ft. If air pressure was dropping significantly at altitude your instruments will be telling you are climbing above max altitude and you, being a good pilot, will descend.
Last edited by Polot on Thu Nov 28, 2019 3:18 pm, edited 1 time in total.
 
Baldr
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 3:03 pm

zeke wrote:
Polot wrote:
zeke wrote:
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.

6% safety margin versus what? The frame wasn’t just undergoing pressurization. When flying at 43,000ft are aircraft routinely having their wings pushed up ~28 ft and fuselage ends pushed down with millions of lbs of force (from article)? We don’t even know if the pressurization was the cause of the failure, and in your calculations you are completely ignoring that the test has a safety margin built in.

To be frank, your “safety margin” number is completely irrelevant and not actually representative of what the real world safety margin would be. If they kept that pressurization and bent the wings and fuselage more to 150% stress and passed would you still be worried? After all that means they still only tested up to 150% of the expect load with a “6% safety margin” when it comes to pressurization.


The test is representative of a pressurised aircraft flying through convective weather at maximum altitude. The way the aircraft will normally encounter loads of that nature are as a result of gusts.

The margin you are talking about is the wing bending moment. The margin I stated was is relation to maximum pressurisation differential.

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.


Actually, it appears as if the failure occurred underneath Doors 3 L/R -- i.e. just aft of the MLG bays.

Hint: Look at the colour of the fuselage in the area of the rupture (i.e the green protective coating).

The centre fuselage of the 777X has the bare aluminium look.

Image of the 777X static test model:

https://www.foxnews.com/travel/test-model-of-boeings-777x-jetliner-shows-incredible-scale-of-companys-largest-ever-passenger-plane

-

Now, the area in which the centre wing box, underlaying keel beam and main landing gear bays are located, is a massive cut-out in the centre fuselage. The combination of a centre wing box pushing wing and landing gear forces into the fuselage in an area where the fuselage has a large cutout for the folded main landing gear, makes this area extremely complex.

Four massive frame fittings (i.e. "pickle forks") are integrated to the forward/rear spars and upper/lower wing covers of the centre wing box, and with the frame fittings being attached to one circumferential fuselage frame at the forward spar and to one circumferential fuselage frame at the rear spar. The upper fuselage skin between these two circumferential frames are bolted to a large structure (i.e. upper cruciform flange).

Hence, it's these massive frame fittings that are the main load bearing connections between the wings and the fuselage, and they have to deal with forces generated by static loads (fuel in the wings etc.) and dynamic loads (wing movement during turbulence / roll etc.).
Last edited by Baldr on Thu Nov 28, 2019 3:13 pm, edited 2 times in total.
 
D L X
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 3:08 pm

raylee67 wrote:
For people asking why the failure matters since the problem happens at such an extreme condition that is so far beyond the maximum in-service load. Because extreme conditions do happen in flight. The plane is expected to fly for 20 or even 30 years. With hundreds of 777X each flying 20 to 30 years, no matter how small the probability is, such an extreme condition is bound to happen on one of the 777X within their service time. Yes, this failure happen when the load applied is almost at the maximum certification requirement. But it still means it fails the requirement. It's not a test that is nice-to-have.


Are you speaking from factual knowledge or conjecture?

Has a 777 (or any plane) ever experienced a load exceeding maximum in-service loads absent a malicious act?
 
Baldr
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 3:20 pm

D L X wrote:
raylee67 wrote:
For people asking why the failure matters since the problem happens at such an extreme condition that is so far beyond the maximum in-service load. Because extreme conditions do happen in flight. The plane is expected to fly for 20 or even 30 years. With hundreds of 777X each flying 20 to 30 years, no matter how small the probability is, such an extreme condition is bound to happen on one of the 777X within their service time. Yes, this failure happen when the load applied is almost at the maximum certification requirement. But it still means it fails the requirement. It's not a test that is nice-to-have.


Are you speaking from factual knowledge or conjecture?

Has a 777 (or any plane) ever experienced a load exceeding maximum in-service loads absent a malicious act?


What's unusual about the fuselage rupture is that it appears to have happened in an area of the fuselage that is some distance away from the centre wing box.

Why would you have a fuselage rupture in that area during an ultimate load test of the wing?

Could it perhaps have something to do with the load bearing properties of the centre wing box?
 
raylee67
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:14 pm

D L X wrote:
Are you speaking from factual knowledge or conjecture?

Has a 777 (or any plane) ever experienced a load exceeding maximum in-service loads absent a malicious act?


I thought I listed CI006 as the example? No, it's not a 777, but a 747. A 747 that survived.
319/20/21 332/33 342/43/45 359/51 388 707 717 732/36/3G/38/39 74R/42/43/44/4E/48 757 762/63 772/7L/73/7W 788/89 D10 M80 135/40/45 175/90 DH1/4 CRJ/R7 L10
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ItnStln
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:22 pm

thewizbizman wrote:
BlatantEcho wrote:
So there was a failure 3x at what is ever expected in the most extreme real life situation ever.

Why is this stuff news?


It was behind what was originally expected. Boeing being Boeing and downplaying it is what is concerning to me. I mean I can't blame them with simultaneous issues on the MAX, 787 Trent's and now this. But their level of transparency seems to be slipping.

The Trent issues are a Rolls-Royce issue, not a Boeing issue. Also it's not the first time a Rolls-Royce issue plagued a manufacturer.
Last edited by ItnStln on Thu Nov 28, 2019 4:23 pm, edited 1 time in total.
 
ItnStln
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:23 pm

TTailedTiger wrote:
thewizbizman wrote:
BlatantEcho wrote:
So there was a failure 3x at what is ever expected in the most extreme real life situation ever.

Why is this stuff news?


It was behind what was originally expected. Boeing being Boeing and downplaying it is what is concerning to me. I mean I can't blame them with simultaneous issues on the MAX, 787 Trent's and now this. But their level of transparency seems to be slipping.


Boeing is responsible for RR's engine issues now? Do you hold Airbus responsible for the PW GTF issues?

Boeing isn't responsible for the Rolls-Royce issue.
 
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:36 pm

Polot wrote:
The tops of thunderstorms actually have higher pressure, it is at lower altitudes/sea level that the air pressure drops and where the meteorological measurements are being preformed.

This is also kind of ignoring how your altimeter is basically just a barometer calibrated to give you a height in ft. If air pressure was dropping significantly at altitude your instruments will be telling you are climbing above max altitude and you, being a good pilot, will descend.


Thunderstorms in the tropics can top over 60,000 ft with strong verticle components depending on the stage of the cycle.

Aircraft fly at constant pressure levels, we fly variable geometric levels.
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Polot
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:44 pm

zeke wrote:
Polot wrote:
The tops of thunderstorms actually have higher pressure, it is at lower altitudes/sea level that the air pressure drops and where the meteorological measurements are being preformed.

This is also kind of ignoring how your altimeter is basically just a barometer calibrated to give you a height in ft. If air pressure was dropping significantly at altitude your instruments will be telling you are climbing above max altitude and you, being a good pilot, will descend.


Thunderstorms in the tropics can top over 60,000 ft with strong verticle components depending on the stage of the cycle.

Aircraft fly at constant pressure levels, we fly variable geometric levels.

Most airlines also try and avoid flying straight through those thunderstorms. If you are at maximum certified altitude and concerned about a strong vertical component would you go into a 60k ft storm?
 
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PW100
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:50 pm

Aesma wrote:
Like others I'm surprised by the over pressurization, I don't understand the point of doing that.


I was wondering whether the (over)pressure would actually help alleviate the compression forces in the keel beam?
Further, I'm sure engineers may want to learn stress and loading paths to fine tune their models. Pressurization might help that as well.

Also I wonder, but this also applies to other failed tests like the A380 one and the 787 one, if it's that easy to reinforce the part that broke : isn't it likely to lead to a weakness elsewhere ?

All the more reason to further improve understanding the load paths.
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zeke
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 4:53 pm

Polot wrote:
Most airlines also try and avoid flying straight through those thunderstorms. If you are at maximum certified altitude and concerned about a strong vertical component would you go into a 60k ft storm?


Because at the levels airliners fly the outside air temperature are so cold the water inside the tops of thunderstorms can go undetected as it’s frozen. Often you cannot see the tops, you see the base on the radar.

Often I fly in weather which includes embedded storms, there is rain and cloud is all around you.
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

Thu Nov 28, 2019 5:53 pm

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

Thu Nov 28, 2019 6:25 pm

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.


Good post and good explanation.

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

Thu Nov 28, 2019 6:42 pm

PW100 wrote:
Aesma wrote:
Like others I'm surprised by the over pressurization, I don't understand the point of doing that.


I was wondering whether the (over)pressure would actually help alleviate the compression forces in the keel beam?
Further, I'm sure engineers may want to learn stress and loading paths to fine tune their models. Pressurization might help that as well.

Also I wonder, but this also applies to other failed tests like the A380 one and the 787 one, if it's that easy to reinforce the part that broke : isn't it likely to lead to a weakness elsewhere ?

All the more reason to further improve understanding the load paths.


The thrust on the aft bulkhead from the 10 PSI air assuming a 19.25' circle is 220 tons which is 6,930 pounds per foot tension in the skin - not trivial. If the skin is 0.063 it is 9,240 psi tension. The hoop stress is 18,480 psi. The probable yield of the skin is 70,000 psi.
 
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Carlos01
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 6:48 pm

On a COMPLETELY unrelated note, I would assume that Boeing probably records all of these tests on video (as any other manufacturer), and probably a very good quality one. I'm just thinking out loud, do you guys wonder if we'll ever get to see the footage of this happening? Like in 20-30-40 years time? If it takes longer than that, my likelihood of ever seeing it goes down exponentially. :-)
 
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caoimhin
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 7:30 pm

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.


Excellent post. Thanks for your level-headed perspective.
 
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trpmb6
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 7:38 pm

Fact is we want the structure to fail. If it doesn't we left weight in the aircraft.
 
d8s
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 8:15 pm

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?
 
d8s
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Thu Nov 28, 2019 8:20 pm

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

Fri Nov 29, 2019 4:42 am

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...
Of all the things to worry about... the Wookie has no pants.
 
OldAeroGuy
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Fri Nov 29, 2019 8:44 pm

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.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
morrisond
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Re: Pictures surfacing of 777X Sept Test Failure - they are Bad

Fri Nov 29, 2019 8:56 pm

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.
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