start with ...
1) do you want to reinforce your strengths, or
2) address your weaknesses ?

if studying, there are many routes, up to full time study.

if getting practical experience, sure playing with mechanical devices is one thing, I'd also try night school for like small engine repair or riveting

are you with a large OEM ? if so, you'll be a small cog in a large machine and probably not see much beyond your particular tube. Look for departments that suit your interests. If you are super lucky you may be with a company that has a rotation program (moving people between departments to get a wider experience). Recognise that this will delay your salary progression.

another day in paradise, or is paradise one day closer ?

Quote (rb1957)

start with ...
1) do you want to reinforce your strengths, or
2) address your weaknesses ?

Thank you for your reply. At the moment, I just want to gain a good grounding in static stress, F&DT, and FEA, before deciding where to specialise further. It feels like there is so much to learn though, and even getting to a basic level in those three things will still take several years.

Quote (rb1957)

are you with a large OEM ?

I am yes, your point about rotations/secondments is a good one and I will look to do that in the future. I am more interested in gaining experience at the moment rather than growing salary.

Then you've pretty much answered your own question !

There plenty to learn in static analysis, plenty to occupy a lifetime !
I'd recommend gaining some proficiency with static analysis (and hand calcs) before venturing afield into FEA or DT.

another day in paradise, or is paradise one day closer ?

A very similar question was asked not-too-long-ago.

IF You haven't already... suggest reading this thread...

best tools - more used (useful) tools https://www.eng-tips.com/viewthread.cfm?qid=489875

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]

Quote (rb1957)

There plenty to learn in static analysis, plenty to occupy a lifetime !
I'd recommend gaining some proficiency with static analysis (and hand calcs) before venturing afield into FEA or DT.

I get that, I'm just not quite sure of the best way to cram all this knowledge into my head.

Is it just a case of endless practice, finding as many practice problems as possible and doing them? Or is it more important to study the theory, by going through the theory to understand everything on a basic mathematical level?

Quote (WKTaylor)

IF You haven't already... suggest reading this thread...

Thank you, I will take a look.

I wouldn't do practice problems, unless to compare different methods ... like one simplification is to use a central pinload for all types of loads ... how conservative ?
or to use UDL in lieu of point loads or partial span distributed loads ... how conservative ? unconservative ??

I think it'd be more useful to analyze a structure with different assumptions, and see the impact. Maybe calculate a true bending stress field, and alternatively look at the moment as a couple on the caps (and shear in the web).

"cram" isn't a word I like (in this ocntext) ... store, retain, and access as needed !?

another day in paradise, or is paradise one day closer ?

Also... most stress-weenies* ... understand very little about REAL airframe structure or related mechanical devices that fit into/rely-on the structure for support.

The very-best stress-weenies* I've ever known have also been factory [or fiel]d liaison/MRB/service engineers and/or aircraft mechanics. Liaison/MRB work requires hands-on-training, in-class coursework and testing for certifications... then get-out-and-do-it for a few years##… then go back to stress. Aircraft mechanics bring a deep-real-world-knuckle-busted-experience to their analytical world. The more extensive the variety of hands-on experience You gain on every part of many aircraft types... the better/more-enthusiastic Your analytical problem-solving skills and approaches.

The very worst stress-weenies* I've ever known have been analytical/FEA literate [some were called genius's, I called them savant-idiots (not to their faces)]... but were insanely clueless about real-world structures... and were often unable to interact with 'ordinary people' to creatively solve the-real-world-problem at hand.

"Experience provides insight" and minimizes "analysis paralysis", IE: inability to define a course of action to resolve/solve complex or obscure real-world problems.

The likewise goes for all other aero engineering discipline... mechanical, propulsion, fuels, electrical/electronics, aerodynamics, etc.

NOTE1. I actually have a document written in the 1970s for a major aircraft company titled 'The Care and Feeding of Mechanical Engineers'. At that time it was recognized that there were genius-level-mechanical engineers who created critical, mechanically complex devices, but had 'special personalities'. These individuals needed specially-sensitive/firm managers/team-mates to support and guide and restrain them thru processes to create real-world hardware in a timely/practical manner, IE: without getting stuck in the minutia.

* all stress guys are weenies.

## CAUTION. Many stress guys reluctantly go back to stress after having worked liaison/MRB/service engineering. ALL retain the spirit of real-world.

Also... the MOST I have ever learned about aircraft/aviation... in concentrated form... is aircraft mishap [accident] investigation training and field-work. This is when Your experiences expands your knowledge/consciousness exponentially.

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]

* ... no reply needed !!

mind you "real" stress guys consider liaison a level below "systems stress" ...

gloves off !

all said in good humour ! Everyone has a role to play, and must play their role, in order that this flying "future accident" gets off the ground.

another day in paradise, or is paradise one day closer ?

"All lies and jest
Still, a man hears what he wants to hear
And disregards the rest"

another day in paradise, or is paradise one day closer ?

A good analyst knows a few things - what analysis needs to be done and what errors will likely be made.

One instructor I had related how his Civil Engineering background got him a job in a missile plant. He did stress work on an adhesively bonded missile body. They did the prototypes, they did the tests, the missile did what it was supposed to do and the production contract was turned on.

Then they did LRIP test firings and the missiles disintegrated in mid-air. I picture them as going up like a puff of confetti, but it was more like separating into segments. So of course they come to the stress guys to demand answers.

They went to the prototype lab to watch. The lab techs measure out the epoxy on a delicate balance, mix completely, clean the mating surfaces with clean new wipes and solvent, evenly apply the epoxy and so on. Then off to production. The factory guys eyeball the components, stir them up real good, then take out the shop rag they've been using for the past week and give it the old wipe - laying down a nice oil film.

Similarly, I worked on an aircraft radar and, after 15 years, the Air Force wanted some spares. So we let contracts to get the parts and get a complaint from one of the suppliers that the weldments were impossible to make. We'd made around 100 of them before, so that was a surprise. They said the had an Air Force qualified welder, one certified in weld repairs. And I thought - I think I know the problem. And, sure enough, because I expect two things from that training. One is that the welds will be free of any and all defects - no inclusions, voids, notches from stops and starts - exactly what we want. The other is that they will be laying it on thick which, since there was a lot of thin material is exactly what we don't want.

It ended well when the guy who did the original program welding went out and showed their guy what's what. It had been taking that repair guy days to do a single weldment, going through a large amount of weld rod. This was reduced to a few hours and very little rod, but still solid defect free welds. I wondered what the original welder charged for the education but since that company said they were amazed at the difference in speed while keeping the quality, I expect they felt it was worth it.

tl;dr Knowing what the field and factory actually do is as important to stress analysis as knowing any book or other technique.

I got my A&P a while back... it's helped... not nearly as much as I thought. I wouldn't suggest it to someone else, honestly I hate sitting behind a desk doing analysis... as that's literally what I'm doing right now. But I've met WAAAAYYY more DAR's doing that than straight engineering. I've seen what is actually done to get things flying instead of engineering science fair projects. Getting to see how things actually wear and break is neat. I have an engine mount bolt on my desk I pulled a few weeks ago with a localized 5% reduction in shank diameter... terrifying. I'm also the guy who is on site for DO160 & MIL-STD-810 testing. Lots to be learned there. One of the primaries at the lab is a Apollo era PhD physicist still going strong who is an absolute trip to learn from.

Am I really good... I don't think so. I do maybe do 2 different style SIMPLE hand calcs, next to an FEA, compare notes, see if it passes my intuition "sniff test" and off it goes. They keep asking so I keep doing it.

Ok Wil, we may be “weenies”, but in the end Stress does everyone’s job (at least those of us who don’t live solely in the fantasy world of FEMs).

Back to the OP,
- study the classic aerospace stress texts - Bruhn, Peery, Flabel, etc
- understand load paths and be able to draw free body diagrams in your sleep, with a pencil
- understand material stress-strain response, for all of the various a/c materials; get experience testing materials
- understand how to determine load distributions in fastened joints, and also joint failure modes
- understand a/c load cases
- understand classic metal structure damage tolerance- fatigue, crack growth, residual strength

I am not a stress guy but being in the business 50 years, know what works.
first of all the floor guys are sharp dudes and know how to build stuff. and all involved down to the suppliers making parts are all important.
but a lot of floor guys have no clue about stress, metallurgical requirements. and how the product is suppose to function.
however give them a drawing and they will build it. it's up to the engineer to design it correctly.
the best way to gain knowledge is experience. and it takes time. don't rush into trying to do what the very experience engineers are doing.
learn from them. listen to the ones who are not afraid and want to teach you. but don't be cocky and pretend you all ready know it.
and don't be high and mighty a round the floor guys. they have a lot of experience how build stuff. you can design some thing and it can not
be built or it is way to expensive. so in a way an engineer has to learn how it's built. in order to design it.

allabright,

In line with what others have said:
1) Make things
2) Bend them
3) Break them

There is no substitute for personal hands-on experience of building and then testing structures to understand how they work and how they fail.

I will address your approaches individually -

Quote:

1) Reading textbooks and taking notes

No, this is maybe the worst way you can spend your time.

Quote:

2) Reading textbooks and doing practice problems

Better, but I would reverse the order. Find books w/ problems and also solutions. Only read the minimal necessary to solve the problem. This is very good use of your time. You must be active in your learning. Spend as much time as possible in actively solving problems. Don't even look at the text until you are certain you don't know how to solve the problem in front of you - then go get that information you need to solve the problem. Then move on to the next problem.

Quote:

3) Reading scientific papers

No.

Quote:

4) Doing little projects, i.e. set up a scenario and try to solve it by hand and with a FEM

Projects is a good idea. But the goal should be to make something. Don't invent scenarios to validate. Come up with something useful to the world. Otherwise, do problems w/ known solutions. The advantage of having solutions is that you can find out quickly if you got it right or wrong. Real world problems are not as straight forward but you actually need something that is real.

Quote:

5) Building on the things I am currently doing at work, i.e. take it further than required, and try to understand it on a deeper level

Never go 'further than required'. Very definition of wasted effort.

Here is something I found very useful - start with learning how to learn -

Learning How to Learn

I used the concepts in this course to great success in self-study. So can you.

I guess I'm the splinter group (I'm ok with that, isn't the first time, won't be the last time)

Practical stuff won't help you with structural analysis. It will help you become a better engineer ... appreciate the difficulty of some things, maybe figure out why some things are the way they are. Getting some time on an airframe (like as a maintenance engineer) will be fantastic experience, but won't directly help you with structural analysis. It will obviously help you appreciate aero-structures on a deeper level, and appreciate some of the non-structural, non-analytical, elements of a plane. Or maybe work "behind the scene" at a airplane museum ?

Even building structures may not help. It may hurt unless the structures you build are like the ones you'll analyze. You could easily "learn" things that are not applicable to airframes.

I would recommend older textbooks, as these will have older more hands on analysis methods. Bruhn, of course, is an excellent text.

I have no problem in taking analysis further than you may normally. I think it builds your tool box to know when some analysis isn't really needed, when it is, and when you can substitute some quicker analysis.

An expression I heard a long time ago "A good stress guy can always find some way to fail any structure". I suspect that this in no longer the common mantra ?

another day in paradise, or is paradise one day closer ?

RB... That Simon and Garfunkel line from 'The Boxer'... is very memorable... and definitely fits into my quotes and truisms' file... Thanks for remembering it for me.

AllaB…

Never hesitate to 'TRY' [my dad's favorite one-word motto].

BE BRAVLY CURIOUS... BUT NOT RECKLESS.
"Fear paralyzes; curiosity empowers. Be more interested than afraid." --Patricia Alexander, American educational psychologist

The real world will always collide with the analytical world. Having a steely eye on reality, ensures analysis makes real-world sense.

A long time ago I discovered that when I understood a problem/issue in all important and intangible details, the 'answer'... the pathway forward... seemed to emerge from the chaos. IF I couldn't see a pathway... I was missing a critical part of the problem.

OH yeah... lots of truth/wisdom in these, taught me by many...

"Life is hard. It’s harder when you’re stupid. -- George V. Higgins

"In theory there is no difference between theory and practice. In practice there is.” –Benjamin Brewster [1892]... but was more recently attributed to Yogi Berra

"The greatest mistake we make - is living in constant fear that we will make one." --John Maxwell, author and speaker

"Remember the Carpenter’s Rule: Measure twice, cut once.” --Unknown

"Measure twice, drill once! -- aircraft industry truism (from Scott Rolik)

"The important thing is not to stop questioning. Curiosity has its own reason for existing.” --Albert Einstein, theoretical physicist

"The cure for boredom is curiosity. There is no cure for curiosity." --Dorothy Parker, writer and poet

"It is necessary for us to learn from others' mistakes. You will not live long enough to make them all yourself." -- Hyman Rickover, American admiral

"What is the meaning of Life??? Your Life… or My life…?” --Guru to Pilgrim [old-Cartoon, author unknown]

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]

I once was in a meeting, where a test fixture was being reviewed; our customer's SME walked into the meeting, looked at the CAD drawing and commented, "Isn't that going to have a resonance around 30 Hz?" He'd never seen anything about the fixture before that moment, and made his comment with barely 10 seconds of study; he was right, of course, the analyst later confirmed a 35-Hz resonance, which was unacceptable per our requirements.

The moral, I suppose, is that it's one thing to be "really good" at analysis by being efficient and accurate and knowing how to structure an analysis, but "really good" can also mean that you intuitively know what the answer is going to be BEFORE you even start the CAD analysis

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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I used to run a modal analysis lab. I also used to build FEA models. I think seeing how things deflect in reality, and the effect of boundary conditions (in particular) and the importance of modelling the test setup helped to make my FEA models better.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

1) Reading textbooks and taking notes
2) Reading textbooks and doing practice problems
#1 & #2 - not generally helpful for practical problem solving since nothing on a plane looks anything like anything in a text book. But it is important to understand the theory behind the tools you're using, otherwise your $20K per year FEA license is just a video game. Know why using von Mises stress to predict failure of a material with %EL of 2% is a bad idea and know which stress will predict that failure.

Buy a copy of Roark (preferably the 5th edition or earlier) and try to confirm the results of any FEA model. We used to have nothing but Roark, Peterson, and hand calculated predictions.

3) Reading scientific papers - most are so esoteric and disconnected from applications that the only value is in learning more about the theory, with a couple of major exceptions. Engineering Failure Analysis publishes papers on the analysis of failures. Participate in failure analyses at your company. You'll learn more useful "theory" during a failure investigation than during any science fair project. But those can be painful and expensive lessons to learn. The strangest, most unexpected things can cause failures.

4) Doing little projects, i.e. set up a scenario and try to solve it by hand and with a FEM
5) Building on the things I am currently doing at work, i.e. take it further than required, and try to understand it on a deeper level

If you're an aerospace stress analyst, read Chapter 9 of MMPDS. Those numbers in the tables are statistically calculated from data. Material strength is a random variable, and so is load.

Doug

Problem with this industry is that substantiating analysis is maintained under tight wraps and is not shared. A person can do text book problems all he wants - but relevancy to real-world problems is not there. Having worked at various OEMS and independent DARS/DERS i have witnessed analysis ranging from multi-page reports to a 1-paragragh sign-offs for the same issue. Different stress engineers have different ways of approaching the same problem .. Case in point are the classic texts Bruhn/Nui/Flabel/Peery - they served their purpose as a great "intro" but lack any meaningful relevancy to today's world of unique materials & situations. They have been around since the dawn of aviation & have not updated - either for sake of liability or confrontation with OEM proprietary data sources. Everyone guards their data & methodology - a design will be distributed - but the analysis kept under lock & key. . Working at an AEO is the best bet in achieving experience - but these days much of the OEM data is is provided in graphs & charts .. where all an engineer has to do is interpret the intersecting lines - without have a clear understanding where this data originated from. Basic principles in analyzing situations is getting more difficult & there are fewer resources to lean on.

Yes, but that is also true of automotive engineering. These days SAE papers are glorified marketing material for nerds, whereas they used to be an actual technical resource. The reason, at least for us, is that developing a new method takes significant teams of people years and can involve dozens of tests. Hence it is far too expensive to just give your competitors for $22. Back in the day we wrote a complete noise analysis suite based on a couple of papers written by a competitor.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

Quote (edmeister)

the classic texts Bruhn/Nui/Flabel/Peery - they served their purpose as a great "intro" but lack any meaningful relevancy to today's world of unique materials & situations.

I think I know what you mean, Ed, but I still get a lot of mileage from these books, with no sign of their obsolescence. Sure, they're no use for a sandwich with CF facings, but most airplane skins and frames are made with the same 2024/7075 that graced the 707 airframe.

I agree with everything else you said, though. Too much knowledge kept locked up in the heads of specialists. My take on that is they are nervously guarding their job security. I am wrestling with this very issue right now - can't get a stress analyst to validate his methods or even provide sources for his equations. They just seem to be coming out of thin air.

At the moment I have to deal with a landing gear cutout. I'm wondering if i have all the bases covered; are my assumptions as conservative as i think they are; have i forgotten some special conditions such as landing impact loads .. Nowhere are you going to find any resources or guidance for this situation. I suppose one could analyze the entire air frame down to last rivet - but there is this minor matter of making a profit. How much time are you willing to invest in this analysis to ensure everything is addressed. In the back of my mind i'm always concerned that the "Federales" will conjure up some issue that i have not considered. Life would be so easy .. if there were some "package" similar to my issue to resource!

Ok, so why should an OEM share their analysis methods and data publicly??