New engineer in the field - needs advice 8

[koopas]

Hello to all:

I am new to the forum. I just started my job after obtaining my B.S. in aerospace engineering this past May. Working as a liaison/structural engineer for a small airline, I feel like I have lots to learn about aircraft repairs. By that, I mean that I am under the impression that I've been immersed into a structural
analysis "subculture" to which I was not exposed to in college, however vaguely familiar some of the jargon is. Lots of quick formulas with no derivations, empirical data, an enormous amount of repair processes (i.e. shim) involving lots of different types of fasteners I've never even heard of.

I am slated to take the FlightSafetyBoeing structural repairs for engineers courses (parts I and II) next month. It seems like I need it.

At work, I've been reading the Mcdonnell Douglas MD11 structural repair course guide, a course that one of my fellow colleague took in 1999. I've also been skimming over Mike Niu's Airframe Structural Design book (1st edition, 1988).

My question is the following: I believe I received adequate theoretical structures in college but all this "applied" structural repair concept is very new to me. Heck, I had to ask how a rivet worked yesterday. Or what a hi-lock was. Or what an allowable is. Reading the MD-11 structural repair course guide (not the SRM), I found that it, so far, all boils down to the following (and correct me if I am wrong) to determine whether enough fasteners are used over a doubler:

1) making sure you add more area than you took out (add more load carrying capacity).

2) determine joint allowable for particular fastener in particular metal sheet. Take lowest value if you use two materials.

3) determine load per fastener

4) ensure that load per fastener does not exceed joint allowable load.

It doesn't look like I'll use FEA. It seems I'll be lucky to see a MC/I calculation. Right now, it's a lot of P/A, material properties, and fastener jargon.

Last, I'd like to know if some of you in the same field had tips and advice on how to become a good airline structural engineer. Can you recommend any literature or training courses to take? I am planning on eventually buying both Niu books (the one I am reading and "Airframe Stress Analysis and Sizing&quot. I understand that experience is an enormous factor.

I feel like I have the knowledge, I just need to apply it.

Thank you for any insight. It will be appreciated.

Regards,

Alex Ly

 

[logop]

hi..
that was a normal problem for freshie graduated. don't worry about your problem. the knowledge that you get from your college will help you understand more about the job that you do now. you just need some time to adapth yourself with your job. i believe uou will enjoy your job soon then after that you can gain your knowledge and maybe invent something new. sometime we can't just learn from reading books, we must experience it and understand so that we can make new way for that kind of problem.


regard

 

[liaisoneng]

Alex:
A key issue for Liaison Engineering is equivalent strength. Your methodology for fasteners is correct, but you must look at the cross sectional area lost, determine the equivalent load it could have carried (normally tensile ultimate depending on the load condition), and determine your fastener count from there.
The Boeing courses are outstanding. I highly recommend them, especially early in your career. I took them unfortunately much later and spent a good bit of time saying, "Yep, made that mistake. Wish I'd known that five years ago."
I believe that in many cases, engineering concentrates too heavily on theory without paying any attention to the realities of the world. Metals are isotropic - what about grain direction? As you alluded to, preparation for fasteners is practically nonexistent. In the Liaison world, it is mainly experience based. Hopefully, you have some experienced engineers to consult and learn from. I think you will find this world to be very rewarding and I wish you luck.
Russ

 

[astroclone]

Universities don't seem to teach much practical information. And in my experience most books aren't that good either.
I recently bought Practical Stress Analysis for Design Engineers. It's available on Amazon.com for $40 (a 59% discount) and you'll receive it in a few days. It has a chapter on Connections analysis which is the best I've seen so far.
I'd suggest all three Niu books, there's one on composites also. Since you are talking about MD-11's I know there's all sorts of composite fairings on that bad boy. I used to work for an airline that had DC-10's, and I'm pretty sure the MD-11 uses more composites than the -10.
For composite work, check out Abaris training.
I was not as fortunate as you to get the Boeing training, but I know it would've helped greatly. The class I was supposed to take was cancelled post 9-11 and then my airline closed.
Anyway, I'm rambling. Just happy to talk to someone who was in the same boat I was in a year and a half ago.
Tony

 

[i278]

My first job out of school landed me squarely in the same territory you describe: designing patches and antenna doublers using nothing more than a shiny new Engineering degree. To say the least, it was a humbling experience--especially in the company of group of technical college grads who seemed to have spent half their schooling learning practical stuff just like this.

Keep in mind, though, that the basics are picked up quickly when working with more experienced engineers, and the basics are the bulk of what you need. You come across the other 95% of material only 5% of the time. Plenty of time to learn that as it comes.

Bully for you taking the Boeing courses. I'd give an opposable thumb for a start like that. Don't underestimate the advantage you're getting from that.

What I've found is that once you have a good analysis reference (Niu or Bruhn), MIL-HDBK-5, the FARs (or equivalent), the internet, and have taken the time to learn how to use them, there's not too much that will stump you. Stump you entirely, anyway.

Good luck; we're all on the same journey.

 

[WKTaylor]

My 2-Cent's worth...

1. The FSI-Boeing liaison course should be a great "starter" for developing sound repairs... however there is a lot more to the liaison and field support engineering positions. I offer the following advice... learned over many years in this type work

2. BEFORE starting any repairs, do a fundamental DAMAGE ANALYSIS. NEVER [EVER] develop a structural or mechanical repair unless the damage mode [mechanism] has been determined. I have seen a lot of well designed repairs fail to "last" because the original condition was not well understood.... hence failed to prevent re-occurrence. NOTE: damage analysis forces each problem into the open and into the collective consciousness. Each problem-analysis then is well recorded and can become part of the formal repair analysis. When this is done, You will begin to identify patterns of damage... by daily/weekly/yearly-cycles, aircraft tail-number, individual components, grades of severity, "old & established", “new and unusual”, operator or maintenance induced, etc....

3. Also, (3) special courses provided me the "ah-ha" insight into aging aircraft damage, that other courses simply failed to provide. Fight tooth and claw for the opportunity to take them… they provide a fundamental understanding of damage, human factors [pilots, technicians, etc], weather, material failures, investigative techniques, technical-photography, etc…


Aircraft Mishap [Accident] Investigator's Course
Aging Aircraft Course
Corrosion of Aircraft Structures
NOTE: See the Fatigue Concepts [training] website for typical examples of "on-site" and off-site correspondence courses....

http://www.yak.net/kablooey/fatigue.html

Also great-to-have courses are as follows:

Fire and explosion Investigator's Course
Metal-Bond and Composites Manufacturing and Repair

4. Take very careful notes on every conversation/discussion, investigation, repair, etc… These notes should be taken for EVERY technical discussion, without fail…. because Your memory WILL fail… when facing many issues a day on different acft, with different people, day-in-day-out. You would be surprised how many times my notes saved trips back to the flight-line or the shop about some “seemingly inconsequential topic”… or when someone desperately needed to know what happened on/about a certain date… or that someone “quoted” me about a discussion for which I had NO records [trying to bull-shit-away responsibility for a problem]… or when I had to review and report on work accomplished.

NOTE: I use a note system where every topic is given a discreet # in a small spiral-wound note-book with both ruled-pages [notes] and gridded-pages [for quick sketches and fastener-tracings]. My preferred system is as follows:

(yy).(###) (date/time) (POC/Tele#)
(acft Type & S/N or tail #)
(discussion, notes, sketches, etc)
(deadline or “political” issues????)

5. In addition to great note-taking, You will have to have YOUR OWN essential hand-tools and safety equipment, such as…

Safety Glasses and side-shields. Face shields work better around chemical processes.
Hearing protectors
6.00”-scale and 12.00” scale [decimal inches mandatory]… and preferred dual sided [inches, MMs]
10+ ft tape measure.
10X magnifying jeweler’s Lupe. A 30X microscope from radio-shack wouldn’t hurt either.
Vernier caliper [decimal inches and MMs]
Angle gage
radius gage set
feeler [thickness] gage set
scribe
small flashlight [IE: 6” Mag-Light] and a “flexible light extension [fiber optic attachment to mag light is available] plus spare light bulbs and batteries
small and “larger” inspection mirrors
“Standard Aviation Maintenance Handbook” [by Jeppesen, or equivalent]
and it wouldn’t hurt to have…
surface roughness gages [judge machined finish quality]
Swiss-army knife and/or “Leatherman tool”
Small GP tool kit [screw drivers, dykes, sockets, pliers, etc]
camel hair brush and disposable cotton swabs
mechanical pencils and extra leads and erasers
grease pencils and or non-lead marking pencils
permanent ink felt-tip pens [many colors, non-corrosive]

NOTE: do not lend-out YOUR tools… You’re guaranteed to loose them!

6. Computer files and Software.

6.1 Maintain a computer file system that will allow You to quickly find/retrieve “similar-to” dispositions and figures. Being able to “cut-paste” from previous work will be very handy. Suggest You set-up file and sub-directories by ATA type or by common usage and tail number… then don’t be too sparing in the file name [long is better… short is hard on the memory]. Be able to trace dispositions [files] to Your notes… and vice-versa! You will appreciate this in the future.

6.2 Get a quick/easy-to-use drafting software [IE: AutoDesk “Autosketch V.7 or later”] that You can extract (and edit) accurate sketches and repair drawings to word documents!!!!!

6.3 Use a good photo editing software for digital and scanned photo enhancement… You can get remarkable detail from a poor photo by enhancing it… and it can be easily edited for size [cropping and resizing] for ease of record-storage and transmitting to another engineer for consultation.

6.4 learn how to take technical photos… it’s harder than You think… but a series of great photos can wipe away all doubt and speed communications. CAUTION: Your photos could wind-up on the internet if you don’t encrypt the files sent to others… and require confidential treatment as such [I have many examples of files sent around the world of “Aw-Shits”!!!].

7. The technicians’ doing the hard work love to work with and engineer who wants to listen to their opinions and EXPERIENCE… and will work with them as equals. They will let-You-in-on things if You have their confidence… and will tell You a side others may NOT know… or want to know. Of course, be cautious about the bull-shit artists… and don’t let “appearances” fool You. Never BULL-SHIT any one [teasing ok when allowed]. If You gain a solid reputation for honest/sincere communication and work, then Your work will actually be easier, cause others will work with You willingly… and sometimes bend-over-backwards to help! Also, remember, that manufacturing [or repair shops, etc…] are under tremendous pressure to “get-out-the-work [get paid!!!]… don’t allow pressure to cloud good engineering judgment… but don’t be too-rigid either!

8. Have Fun… Liaison work is the most unique combination of theory and hands-on experience You could possible get… short of accident [or failure] investigations. You career aspirations will only get added credibility as a stress engineer, designer, M&P engr, etc… having liaison as a background!!!
Regards, Wil Taylor

 

[WKTaylor]

koopas ...

I forgot to mention one VERY important point, that turned out to be MY "hardest lesson learned" as a young engineer: when You write a document that solves a liaison type problem [repair procedure, NDI/maintenance procedure, etc], follow a very rigorous methodogy, every time. My own documentation "methodogy" [and rational for it] is as follows.

a. ID #, equipment #, P/N, S/N, Acft Tail #, etc
b. Accurate subject [title].
c. Background and problem statement.
d. Non technical References [telecons, inspections/dates, messages, etc] and Points of Contact [POCs] and Contact info [email, tele, address, etc]
e. Technical references [SRM or T.M./T.O. data references, Drawing #s, etc...
f. The procedure.
g. Documentation requirements [IE: log-book write-up, etc].
h. Insure Your name/address/etc in margins [plus data-file retrival info!]. Also add Your siganture [digital or scanned] at the end; and lock the file as "read-only"!

NOTES:
a. Use simple ACCURATE, technical english. Dont embellish or use NON-STANDARD words or phrases. SAE (and AIAA??) has a great technical aerospace dictionary: USE IT, or Your own company's dictionary!!!! Same goes for abbreviations!!!
b. Insure that the solution matches the problem! Duhhh... but You would be surprised what creeps into a document... or how "poorly" you have worded something. Get a good technical english book and USE IT... to insure the correct tense, verbage, etc! Avoid colorful phrases and
c. Write Your documents such that anyone NOT associated with "the problem" could read YOUR document, plus all other referenced documents, and fully understand what the problem was and how it was to be solved [IE: Your disposition, etc]. If Your document can be picked out of the files 10-yrs from now, and be fully understood, You have done Your duty to the company and the engineering profession. This may seem tedious, and can be a royal pain [english was my worst subject in college], You have to remember that this document is part of Your "proessional-legacy". NOTE: If You also need MORE motivation to do the "paper-work" coreectly, then remember that lawsuits are often "won or lost" based on the quality of documentation [even 20-yr old documents]!!!
Regards, Wil Taylor

 

[mikero]

Astroclone mentioned earlier a textbook called "Practical Stress Analysis for Design Engineers". It's an excellent book to help you understand loading conditions that design engineers have to consider, as well as the type of structure which is typically used to resolve certain loading conditions. The better you understand the loading conditions, the more prepared you will be to repair the damaged structure. As Will stated, "NEVER [EVER] develop a structural or mechanical repair unless the damage mode [mechanism] has been determined."

There's a year-long distance-learning course associated with this book. I am a little more than halfway through and I think it's been extremely helpful. They will probably mention this course during your FSB Structural Repairs for Engineers course as a suggestion for further study, as they did when I took the FSB course in April 2001. As an aside, I think the FSB course is incredible.

Anyway, the website for the PSA course is:

http://www.psa1.com/correspondence.html

Have fun!

 

[inertia4u]

Wil Taylor,
You know I love your post, but you've seem to miss 2 very important points for any engineer working on airplane repairs:

1. Free Body Diagram all your repairs.
2. Make sure your FBDs are balanced!


Nert




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Nert

 

[WKTaylor]

Inertia4u...

My first post started out with the following paragraph...
"The FSI-Boeing liaison course should be a great "starter" for developing sound repairs... however there is a lot more to the liaison and field support engineering positions. I offer the following advice… learned over many years in this type work."

The FSB course Alex Ly is taking will concentrate on analytical concepts of repair design… including the FBD concepts You mentioned. Analytical aspects of “the job” are intrinsically easy for 99.9% of engineers to grasp.

I believe that You may have missed the point of my (2) previous posts. Considering that everyone's post prior to mine mentions various/significant analytical aspects of [liaison] engineering analysis, I did not believe that restating any of this would be of assistance. My posts were intended to highlight career-enhancing subjects/issues... and provide some of subtle, and not-so-subtle, lessons-learned at a real-world "school of hard-knocks” as a working engineer. It has been MY experience that the working territory peripheral to the job of being an “engineer” is the hardest aspect of the job to learn!!!
Regards, Wil Taylor

 

[inertia4u]

Oh, I hope you didn't take me the wrong way, which it seems to me you did...and just so you know, I don't think I missed anything from your very informative posts. I would have just added the statments about free body diagrams.

Analysis methods and FBDs are two different things - so I wouldn't really say that they were already discussed in this post. Understanding load paths is great as well, but documenting the load path is a very important for the follow-on engineer.

As I am sure you know, an engineer can do 1 FBD and do over umpteen different variations of anlayses on it. Also, I may understand the load path of a specific skin shear tie widget, but if I don't communicate that idea to you via an FBD in my documentation, how would you know what to do if the widget was to modified by a customer?

Why am I making a such a fuss? Well, just as you eluded to in this thread, documenation is very important. And as I see it, any repair developed that invovles altering or restoring load paths should be Free Bodied and be included in the technical write-up any liaison engineer completes. That point was not included in any post for the question asked - and I thought it would fit nicely in the section where you are talking about your documentation methodology, that is all.

Nert

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Nert

 

[knobhead]

wktaylors post is one of the best I've seen on this forum, and I think that should be printed out and given to new enigineers, regardless of thier discipline.

I'd like to say that point 7 is probably the most important part of that. The guys on the floor know EVERYTHING, and if you come over like a patronising idiot, they can, and will, make your life incredibly difficult. It's hard, just leaving college, to suddenly realise that you know NOTHING, but swallow your pride and ask these guys. They will teach you more than anything you can imagine, and I think they generally get a kick out of teaching the college kid... Excessive accuaracy is a sign of poor breeding. -Socrates.

 

[johnfalky]

Well, the guys on the floor, like all of us, ASSUME that they know everything. As an individual who started in the race car business in Europe, then transitioned to Aircraft Manufacturing, then to maintenance and heavy repairs, I have seen a lot of incorrect "tribal knowledge" that becomes embedded and is then assumed as being "technically correct". However, when I have told folks that they aren't drilling or reaming a hole correctly, that hands-on tech experience is good, because I CAN grab a drill motor and I CAN show them that there ARE Engineers that CAN drill holes correctly, and this goes a long way toward a good relationship, often finding folks in your office at 6:30 in the morning because they have a problem and they want you to look at it, so they can solve it and continue work. Teamwork is the absolute neccessity in this kind of environment to get work done correctly, to a very high standard. When a big repair is completed, this gives the whole crew, both techs and Engineers, a great feeling of accomplishment and confidence.

 

[astroclone]

Johnfalky points out the flaw in being good and respected.
How in the world can I get in my web surfing/ coffee/ nap/ bathroom breaks/ smoke breaks/ and so on if I have mechanics in my cube every 6 seconds?
Nope, all you got to do is call a bolt a rivet and ask the mechanics what transfer function they are using to install the doubler and they'll steer clear!
T

Just kidding, it feels like a monday again.

 

[junkhound]

Only now just found this site.
Could add one item to watch for to list in original post that is often forgotten - that is hole tolerance and the zipper effect - which I never heard about in school many years ago.

 

[johnfalky]

I have seen 1 incident of "zippering" in a pressure bulkhead of a large aircraft where it was struck by a pallet that had come adrift on takeoff. The bulkhead "ripped" from fastener to fastener, actually looking like an open zipper. (Was repaired by replacing everything) However, I have seen another phenomenom in a new skin that had been installed with preload in a manufacturing fixture (obviously incorrect).
As the skin was forced into place and drilled for rivets, one of the holes developed a propagating crack that could be visibly seen as "moving."
Attempts to stop the cracking by "chasing it" i.e. trying to drill a hole at the tip of the crack were fruitless. The crack spread in an almost "liquid" manner. After consulting with management and Engineering, work using this fixture was stopped. The skin panel was scrapped and the preload condition in the fixture was corrected.