Structural analysis report examples 3

[eix]

Hi, I've been wondering if you have ever encountered some old, publicly available aircraft structural analysis reports? I am well aware this is highly proprietary data but would they not release a report from e.g. 1940, 1950? I bet you could learn a lot even from such old document and it would be super interesting. Is there some public web archive with such documents?

 

[GregLocock]

Sure the NACA report archive has lots of historical reports

https://ntrs.nasa.gov/citations/19920013725

Cheers

Greg Locock


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[eix]

Thanks Greg, that’s a lot to go through. Do you think I might find there a structural analysis substantiation report of some airframe? Also, what are chances of finding substantiation documentation of old commercial aircraft like for example DC-3, or any other? I imagine manufacturers don’t have to and have no interest in publishing such documents but on the other hand is there any risk whatsoever in doing so? I am very interested to see how they dealt with structures before computers. Especially on a global level. I know examples from Bruhn but would like to see more applied on a larger scale.

 

[MintJulep]

See this old thread for some things that might interest you.

thread2-401728

 

[eix]

thanks Mint, I also realised there is

https://discover.dtic.mil/

I'm looking for docs like this one

https://apps.dtic.mil/sti/pdfs/AD0657997.pdf

It seems that universities have vast collections but not easily available.

 

[rb1957]

why do you want this ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Sparweb]

The XV-5A report is interesting, and appears to be a rather good example. The author proceeds from illustration to loading to detailed structural design, arriving at margin of safety. If anything was missing, a free-body diagram would be welcome... but in many cases the forces are already dictated at the point of load in the illustration, so the structural system doesn't need further decomposition. This report is Volume 3 of a series, so it is probably necessary to have the other volumes and cross-reference the data and conclusions before accepting the contents of this one.
Great find!

 

[WKTaylor]

In school we studied elements of design and analysis. In the real-world of design, the methodology of design-build-test-produce is the proprietary 'ART' of the people putting their heart and soul into the project. In this process there are huge technical challenges and risks to-be overcome... thru the entire process.

The resulting design, 'drafting', analysis, testing-testing-testing-etc is a multi-iteration loop getting close-enough to a solution that 'cutting metal and testing real 'hardware' is the outcome. In today's digital world, numerical simulation... creating a 'digital-twin' of design concepts... speeds up the process by eliminating/shrinking thousands of hours of ideas leading trial/refinement and ultimately prototype manufacturing.

Ultimately, these design iterations boil-down to an optimum trial-design which is found suitable/confident for building and testing real prototypes... and preparing for production. THEN during real-world prototype testing... static/dynamic structures and systems... and then the fully integrated flying-test aircraft... leads to a final 'frozen' configuration suitable/confident for certification and limited production.

Of course, this process is all relative in every aspect and the 'trajectory of the design-path' can be grossly altered based on acceptable RISK, overall COMPLEXITY and the level of EXPERIENCE of the design-build teams [PEOPLE].

Highly experienced design engineers and staff... working in very small teams... have successfully designed [or preliminary-designed/outlined] some of the most famous and prolific aircraft using streamlined and 'light/minimal' design practices... then build/test/refine... often with a human cost. RISK.

Hint. NOTHING in this process with professionals is ever spontaneous... and every element factors in and is 'built-upon'. Here is a glimpse of what I mean...

Preliminary design. Sketch-up[cartoon] a vehicle based on mission requirements, mass/weight/balance, aero/inertia/gravity, parts, materials, engines, mechanical/electrical/payload systems, etc.
Refine the preliminary-design cartoon as pieces 'solidify'.
Establish real-world aero-shapes, weight-balance, aero-loading, etc.
Create preliminary design drawings of assemblies/installations... suitable for expanding the design process for each element.
Preliminary aero/stress/systems analysis and refinement.
Create more-refined/detail drawings.
Interim aero/stress/systems analysis and refinement on what is emerging.
Detail design of structures/systems/arrangements, etc.
Final-prototype and refinement and review of the design of structures/systems/arrangements, etc. Does it all make sense and 'fit-together' as a system-of-systems?
NOW, proceed to write/publish the pre-FORMAL [pre-flight] aero/stress/system analysis and testing as needed.
NOW, build/test/fly the prototype articles.
... ...
etc...

THERE IS NO GETTING AROUND that is a process... and the stress analyses that You are thinking about evolves within the process is progressive... so that the published FORMAL analysis [and subsequent refinements/modification] occur after this initial peak. EVERYTHING in this process is built/refined on/over the mountain of hard-work, hidden underneath it.

What is 'sadly curious' is when new engineers and designers step-up and expect to create miraculous 'inventions' without understanding the multi-stage processes and basic experiences required to accelerate 'the process'.

Hint SpaceX has made huge/amazing advances in space-flight launch vehicles... based on the prior experiences of missile designers and the treasure of data generated by NASA and the DoD... AND WITH the experience of older HIGHLY engineers and technicians sprinkled through-out the organizational structure. AND it was a strategic choice to create a SpaceX mega-center/HQ in the heart of Southern California... where there is a huge/eager experienced workforce in aerospace missile/space-vehicle design and manufacturing.

I'm tired and need to start punching the clock. Sorry, this post has gotten waaaay off-the simple track of Your inquiry.


Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[eix]

rb1957 for educational purposes, to see theory put into practice. I think there’s hardly better source to learn stress analysis than completed reports. By the way, I am surprised it is necessary to dig so deep to retrieve such excellent educational resource such as old reports, and that they are not popular. You hear Bruhn, Niu, Peery, Flabel.

 

[SWComposites]

I think there’s hardly better source to learn stress analysis than completed reports. wrong - the best method is to learn under the direct supervision of experienced stress analyst lead engineers while working multiple aircraft programs. As Wil says, there is WAY more behind the formal analysis reports that is critical to an acceptable analysis.

And ..... what is the incentive for any company to make their old stress reports publicly available?

 

[eix]

Swcomposites… books are praised for real world examples…..why not just look into the original source?

Wrt your best way… say that to a student (i am not)

This discussion is going nowhere.

Wrt making available - some reports are made available, eg the one I linked. So my answer to your question is why not?

 

[rb1957]

I think reading another stress report is a very bad way to learn ... unless the report is exceptional. Most reports will skip steps the author considers obvious ... or steps that would be obvious to a professional reader. Most are not written as "school assignments", taking every single step back to the most fundamental concepts.

Reading another stress report it is very easy to follow along with the author, rather than to question "why'd he do that ?" or "why not this ?"

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[GregLocock]

Product liability is the main reason I think. If your airplane crashes and there's an error in the structural analysis then the prosecution will allege that that is typical of the standard of engineering on the machine.

Cheers

Greg Locock


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[GregLocock]

Or to put it another way, what advantage is there in telling your competitors how you do things? That did use to happen, but in the last 30 years that's disappeared.


Cheers

Greg Locock


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[Sparweb]

Eix,
This discussion is going nowhere.
Sorry you feel that way. There may be a disconnect between your expectations and the information being provided.

Let me try a different kind of example. How do doctors learn their profession? How do lawyers? Dentists? They need a practicum (or residency, or article, or some other term that means they practice or apprentice under the guidance of others in the profession). For some reason, engineering (in North America) has not instituted quite such a formal process, but it is necessary nonetheless. Such a practicum was explicitly practiced recently in some European countries but I'm not sure it still is, given the race for the bottom that many of our governments and educators engage in.

Another factor that blocks an easy answer: the data in most engineering reports is treated as proprietary. This is different from many other professions who publish their methods openly in scientific journals, and of course Western courts of law are open to the public. Engineers who want to publish their methods work in academic spheres, the rest who work in private industry guard it. Therefore what you're asking for is the very thing that is protected by economic interests. Engineering reports that you can get, when you can get them, are likely to be released for unusual reasons. Perhaps developed for a public or government agency, who released it, etc.

So, as long as you are willing to accept that you aren't really learning the whole art of engineering by reading stress reports, new or old, then you can have realistic expectations that you can get an idea of some of the techniques used. But many other forms of judgement won't come until you really get into the practice and have to balance competing interests, costs, goals, and resources available to accomplish them.

I am still racking my brains for some useful examples that I can show you...

 

[Sparweb]

Here is where you can download a copy of GAMA publication 13 (Cabin Interior Monument Structural Substantiation Methods)

https://gama.aero/facts-and-statist...ry-technical-publications-and-specifications/

That's an analysis and report-writing standard that captures some of the judgement and methods you need for a specific type of structure; interior monuments like cabinets, bulkheads, galleys, etc.

They have plenty of other technical topics, too, but that one deals with structural analysis directly.

 

[Ng2020]

Despite what others may say here, I think a great deal can be learned from reviewing stress reports good and bad (once you have a good understanding of the basics). Though the stress report is just once piece of the puzzle.

A while back I saw a skylab stress report on the nasa ntrs. It related to crew restraints, cabin furnishings and the like, nothing as exciting as fuselage structure.

I think your example is the best I've seen yet in the public domain. And it's pretty typical of what you'd find inside an oem from that era. Keep looking on the NASA library, seems like it's your best bet.

 

[crackman]

Dear eix

It is indeed a great idea to go back and look at past structural analyses. In all my years as a DER, structural reports have progressively gotten worse. Also, much analysis is performed via FEA but many engineers do not correctly validate them as they do not know how to perform the classical analysis. Anyways, yes, there are a large number of structural reports which are public domain. Of course, these are related to projects which were funded in the past by the various governments primarily for military purposes. However, even though they are public, they are difficult to locate and they are not free. I have been researching at the US national archives, the UK archives at Farnborough and also at DSTO in Australia for over 15 years as part of an Airframe Fatigue Handbook which I am authoring and also the DTA class which I teach twice a year with a good friend of mine. I have found and obtained hundreds of stress reports over these many years but you must pay for the reproduction fees which can get considerable. A single stress report depending on size could cost $500 to $1000. Anyways, here is a short top listing of aircraft for which I have verified and obtained aerodynamic loads, structural loads, fatigue loads, internal loads, stress reports and even static and fatigue test reports for over the past 15 years.:

Boeing B-17, Convair B-24, North American B-25, Martin Aircraft B-26, Douglas A-20
Curtiss C-46, Douglas DC-3/C-47, Douglas DC-6, Lockheed L-1049, Lockheed P2V-4/5/6/7
Convair 240, Convair 340, Grumman F4, F6, F7, F9, Chance Vought F4U, Boeing F8
McDonnell F3J, Bell 47, and many others

Anyways, for later model aircraft, I have obtained great stress report and even fatigue test reports for aircraft which are no longer in military service and for which the documents have been declassified through the FOIA process. Again, public domain does not mean free or that it is quick. In many cases, it takes several months to get photocopies of just a few reports. However, I have found them to be invaluable. They illustrate the analytical methods, analysis and even correlation to test data. For more modern aircraft, our government acquisition folks are not shrewd enough to make sure the vendors provide reports that are government owned. For instance on the latest FXX fighter, the government paid for R&D development, engineering, production, basically all of it but allowed the vendor to label everything proprietary when in fact all of us tax payers paid for 100% of it. Just very poooor contracting IMO.

Anyways, I have thought one day to donate all my public docs to my alma mater, if I do, will let you know. In the mean time, I recommend contacting the archives and spend some time researching and you will find what you are looking for.

Best of luck

 

[eix]

Great input crackman, thank you. When I started this thread I knew how small chances are that they published eg a dc-3 report (let alone you could actually access it), yet your post exceeded my hopes and expectations. At least now we know that past reports are accessible in some way. Can you say if any of the reports was readily available for download, or you had to request a reproduction for all of them? How does the reproduction process look like, is it remote or you have to participate on site?

 

[crackman]

Hi eix

Unfortunately the process is not easy. First of all, there are numerous archives and their search engine is not very good. Once you find the report you are interested in, you can place a request for quote which is limited to a max of 3 documents. Then it takes about 2 to 3 weeks to get a quote. You can request either a photocopy or pdf, but the pdfs are not high quality so they suggest photocopy if figures are included. If you choose pdf, they eventually upload it after about 2 to 3 months and you have a limited time download after which they delete. They do not keep the pdfs.
They do however have an extraordinary amount of data. For example, for the DC3 and DC6, i have the loads report, fuselage monocoque stress analysis, fuselage frame and bulkhead stress analysis, pax and cargo door cutout analyses, wing box analyses, wing spar analyses, empennage analysis, static structural test, panel allowable test, ect. So, definitely worth the wait.