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737 NG cracks ? #5234457 10/09/19 04:14 AM
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Exhaustgases Offline OP
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https://www.youtube.com/watch?v=HqR55tfIr7Y

That must be a good sized part and very difficult to remove and replace. Any one know what all is involved in doing that?

I would be real curious how many old slide rule, designed aircraft had AD's on cracks? Could be more proof that the modern computer fea and other systems are not all that great after all. Its just crazy to see some of the design work on something like the old C97 engine mounts and what they had to take, then there was the structure in the wing nacelle's. Those old timer engineers where the best.

Last edited by Exhaustgases; 10/09/19 04:22 AM.
Re: 737 NG cracks ? [Re: Exhaustgases] #5234635 10/09/19 08:32 AM
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Originally Posted by Exhaustgases
I would be real curious how many old slide rule, designed aircraft had AD's on cracks? Could be more proof that the modern computer fea and other systems are not all that great after all. Its just crazy to see some of the design work on something like the old C97 engine mounts and what they had to take, then there was the structure in the wing nacelle's. Those old timer engineers where the best.

They all do. There are many structural crack related ADs for legacy airplanes, even those that are typically considered "overbuilt" like those from McDonnell Douglas.


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Re: 737 NG cracks ? [Re: Exhaustgases] #5234642 10/09/19 08:39 AM
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Aluminum has a fatigue life. Then it cracks. it is well understood and predictable within limits.

Everything has a life time.

Rod

Re: 737 NG cracks ? [Re: Exhaustgases] #5235341 10/09/19 10:08 PM
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Exhaustgases Offline OP
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I know those 131 Hercules had some problems keeping the wings on.
I don't think any of the old designed Boeing planes had the problems we are seeing now, with the NG cracks and the Max 8. I guess there was the control valve issue with an older boeing plane. But how about 707 and 720's? They seemed to be some of the best Boeing planes.

Re: 737 NG cracks ? [Re: Exhaustgases] #5235769 10/10/19 10:53 AM
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kschachn Online Content
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Originally Posted by Exhaustgases
I know those 131 Hercules had some problems keeping the wings on.
I don't think any of the old designed Boeing planes had the problems we are seeing now, with the NG cracks and the Max 8. I guess there was the control valve issue with an older boeing plane. But how about 707 and 720's? They seemed to be some of the best Boeing planes.

There are many airworthiness directives for the 707, you can go to the FAA website and see them if you wish.

Another consideration is that for old airplanes there are repair assessment programs and aging aircraft tasks required to preclude failures and subsequent ADs. So even if there isn't a structural AD for something there still can be extensive inspections and repairs required for airframe safety. As an aside, for the 707 compared to the DC-8 many of these assessments are required at a lower threshold and increased frequency for the 707 compared to the legacy Douglas product.


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Re: 737 NG cracks ? [Re: Exhaustgases] #5235886 10/10/19 12:46 PM
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Originally Posted by Exhaustgases
I know those 131 Hercules had some problems keeping the wings on.
I don't think any of the old designed Boeing planes had the problems we are seeing now, with the NG cracks and the Max 8. I guess there was the control valve issue with an older boeing plane. But how about 707 and 720's? They seemed to be some of the best Boeing planes.

Maybe the engineers should go back to the old school of flying and let the pilot do more without all the automatic flying computers....our WW2 B17s made it from England to Germany just fine...


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Re: 737 NG cracks ? [Re: Exhaustgases] #5235899 10/10/19 12:53 PM
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Originally Posted by Exhaustgases
...Could be more proof that the modern computer fea and other systems are not all that great after all. Its just crazy to see some of the design work on something like the old C97 engine mounts and what they had to take, then there was the structure in the wing nacelle's. Those old timer engineers where the best.


I did Finite Element Analysis (FEA) and Dynamics Analysis on the 777 and there is nothing wrong with FEA. However, the engineer has to have a good understanding of Structural Analysis and Aeroelasticity. The old adage of, "Garbage In, Garbage Out" also applies here.

Slide rule analysis was good to two or three decimal points, FEA is good to 64 bits or higher precision.

The older planes were designed with slide rules but there was a lot of "added strength" fudge-factors going on (because of uncertainties in analysis) so the planes were a lot heavier than needed. Ever watch the Buffalo Airways segment on the Weather Channel? http://www.buffaloairways.com/

In addition, Strength of Material's testing machines are a lot more sophisticated today than they were in the 40's and 50's so better material's data can be fed into the FEA suite.


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Re: 737 NG cracks ? [Re: Exhaustgases] #5236084 10/10/19 04:06 PM
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CAD design allows engineering to remove any extra durability when manufacturing parts,,,, no? I have a friend whos life time career at United Airlines MOC in SF as an A&P would say planes gained weight as they age due to the repairs. Planes see lots of stresses even with the most mundane operations.


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Re: 737 NG cracks ? [Re: CT8] #5236516 10/11/19 01:17 AM
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MolaKule Offline
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Originally Posted by CT8
CAD design allows engineering to remove any extra durability when manufacturing parts,,,, no? I have a friend whos life time career at United Airlines MOC in SF as an A&P would say planes gained weight as they age due to the repairs. Planes see lots of stresses even with the most mundane operations.


CAD manf. allows excess material to be removed which reduces weight and CNC allows a higher precision in manf.


"You ... sadist," said Mr Cummings, "you try to make people think." Ezra Pound (1885-1972)
Re: 737 NG cracks ? [Re: MolaKule] #5237061 10/11/19 02:19 PM
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Originally Posted by MolaKule
Originally Posted by Exhaustgases
...Could be more proof that the modern computer fea and other systems are not all that great after all. Its just crazy to see some of the design work on something like the old C97 engine mounts and what they had to take, then there was the structure in the wing nacelle's. Those old timer engineers where the best.


I did Finite Element Analysis (FEA) and Dynamics Analysis on the 777 and there is nothing wrong with FEA. However, the engineer has to have a good understanding of Structural Analysis and Aeroelasticity. The old adage of, "Garbage In, Garbage Out" also applies here.

Slide rule analysis was good to two or three decimal points, FEA is good to 64 bits or higher precision.

The older planes were designed with slide rules but there was a lot of "added strength" fudge-factors going on (because of uncertainties in analysis) so the planes were a lot heavier than needed. Ever watch the Buffalo Airways segment on the Weather Channel? http://www.buffaloairways.com/

In addition, Strength of Material's testing machines are a lot more sophisticated today than they were in the 40's and 50's so better material's data can be fed into the FEA suite.



If it wasn't for the "old guys" and the stress analysis techniques that they developed, what 100 years or so in the past FEA would not exist. Slide rule accuracy?
Yeah I actually know how to use one so. In the ww2 days they also started using mechanical calculators and into the 60's, that where much more accurate than slide rules, I mentioned slide rules to point out what was accomplished by people that actually knew what they were doing and didn't have fancy computers and software to make up for lack of knowledge like what exists nowadays.

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