Detail design process 1

[Gann]

Hello, I've been working on a large program in the industry for around a year now in a co-op program while I'm finishing up school. I'm doing my senior design project right now and I keep getting hung up on little detail design items. For example, different ways to make a bracket. I've heard it said many times that detail design is one of the hardest parts of design engineering. As a design engineer in the Aerostuctures side of the industry it seems like detail design is what I'm going to be doing the most. I'm wondering how you all go about designing different parts, like brackets for example. In many other industries I feel like looking at other examples is a much more simple task, even though it might not be the most "progressive." But I cannot just google how Boeing mounts their inboard landing light on the 737, in aerospace looking at the example of the competition is often times impossible from what I can see. This may be true in other industries as well, but I could imagine an engineer at Ford looking at a Toyota design for some "inspiration."

So, my question is, what is your process for designing things like brackets or other structural items in the best way possible? Are there places to look for examples? Or is there some other way that I'm missing? Thankyou for your time. Also, if this is not the right place to post a broad question like this feel free to move it. I'm in this industry but I feel like this is almost an all encompassing "mechanical design" type of question.

 

[rb1957]

Over time you'll build a folder of design examples of how your company has done similar things in the past, how other people do similar things.

Boeing used to have an excellent design handbook, showing different designs that were good, bad, and ugly (and so why to avoid the ugly ones) ... someone stole my copy !

But I doubt anyone's going to tell you this is how to design a cleat/clip/gusset/... part of the problem is different companies do things different ways, prefer different designs, materials, ...

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

 

[Sparweb]

Michael Niu's Airframe Structural Design book is illustrated with many do/don't examples.
Bruhn's Analysis and Design of Flight Vehicle Structures also has several chapters with detail design recommendations and simple analysis techniques.
Same goes for Flabel's book.

Since you're in a "large program" right now, you are probably exposed to many many slight variations of 1 preferred design method. Stick with them and you will come to know it intimately. The flip-side would be to work for a MRO doing work on a variety of aircraft. My early experience, sticking my head in helicopters, light planes, jets, new and old for 15 years... it was hard to build up a consistent picture of how anything "should be done" but eventually certain rules became clear, and other apparent rules became transparent.

One suggestion, if you don't think you will get such a varied experience, and want to see how aviation structural design has evolved over 114 years, is to spend a lot more time in museums, perhaps even volunteer. Just when you think you understand something, you will peer inside another relic, and discover another secret.

I also recommend that you keep a library of do/don't examples of your own, as you move from project to project.

STF

 

[WKTaylor]

Gann...

In addition to what rb1957 and SparWeb have clearly stated.

IF PRACTICAL...

When a simple/useful configuration ‘example’ exists elsewhere, then consider creating something 'similar' [plagiarized] parts... unless, of-course a radical departure is MANDATED for technical reasons.

Use standard configuration extrusions or sheet metal 'formed shapes', materials [alloys] and fastening practices where practical.

Avoid parts that require heat treatment due to forming complexity [IE: tight bend radii that can't be cold-formed, etc]. Machining or cutting/trimming an extrusion to shape might make a part that could be: stronger, tougher, lighter, expensive, simpler than a formed part that has to undergo heat treatment.

Always keep in mind whether something is: (a) ‘value added’; (b) ‘cost/weight-avoided’; or (c) ‘gold-plating’ [unnecessary, costly, etc]; simple/complex; etc!

I have seen side-by-side configurations that are made, assembled and installed differently... only to realize that multiple-designers took multiple arbitrary/unique paths to the same end... which drives the shop, logisticians, analysts, tech data writers, service engineers, etc NUTZ!

Structures-to-structures brackets are different than structures-to-systems [EE-EL, mechanical, pneumatic, fluid, etc] brackets.

Watch-out for loads/reactions that may change due to strain/flexure... or if improperly/inadequately restrained. Examples:

Pneumatic ducts and hydraulic tubes/hoses ‘do the funky-chicken’ when experiencing pressure and flow fluctuations: if improperly restrained these movements end-up damaging themselves, couplings and their attachments. Likewise G-loads and structural flexure [in-flight structural spectrum loading] may feed-back between the structure-brackets-system adding strain/flexure.

Electrical wiring/harnesses appears static but structural flexure and G-loads [spectrum loading] feed-back can be a great concern. Too much or too little constraint can be a real problem. The A380 had improperly sized/mounted wire harnesses/wire-runs/bracketing which 'broke/tore' during initial flight testing.

Vibration and sonic-vibration considerations may also be necessary.

Be aware that components under thermal-acoustic insulation or in condensation drip/drain-paths can experience significant moisture exposure or moisture accumulation/trapping hence corrosion potential. Be specifically concerned if other fluid [toilet/urine, oil, fuel, etc] 'puddling' [accumulation], is likely to occur.

Consider how YOU can make bracket installation ‘dead-simple-accurate’ for the mechanics to install! An engineer that is not thinking into and ahead to the actual installation might miss an opportunity for accuracy, simplicity, problem-avoidance, cost-avoidance, etc. Can simple templates or tooling or matched-hole-locations ease the installation and ensure accurate placement of parts?

There is nothing worse than secondary-structural parts added to primary structure as a ‘sloppy-after-thought’.


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]

 

[MikeHalloran]

A designer arrived at my tiny company, having 8 years' experience designing fuel line brackets for one side of a particular jet engine, and nothing else. He never saw an actual engine, or even drawings for the other side. That's detailed. It took a while to widen his perspective.

I agree; visit museums to steal ideas and do comparative anatomy. Also boneyards.





Mike Halloran
Pembroke Pines, FL, USA

 

[Sparweb]

Ooh, yes boneyards. Good suggestion, Mike. Knowing what happens to the structure when it rots away, gets abused, or meets some other ignominious end is of great value, too.
I gained an appreciation for the energy absorption capacity of sandwich panels after seeing a number of wrecked helicopter frames.

STF

 

[WKTaylor]

SparWeb...

Good point about museums... especially for viewing how many companies 'do-the-same-thing... but differently'! A hydraulics' buddy was mind boggled looking into an ancient F-105 bomb-bay, hell-hole(s) and engine-bay. Came-away appreciating combat aircraft hydraulic-system evolution!

Boneyards are harder to find except in desert environments. Flyable aircraft in storage may be untouchable.

Some companies have design guides, lessons-learned, service/failure experience, etc, documents that might be useful.

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]

 

[3DDave]

A few years back I had the chance to visit the museum in Huntsville. I was looking at a detail on a rocket motor when a guy came up and asked if I was an engineer. I told him yes, and asked about his question. He said he thought so, because most museum visitors don't spend much time looking at the exhibits**. He said I was fortunate because most of these engines had only recently been pulled from storage. They were taken out for the Constellation program because NASA, et al, had lost so much experience in rocket motor design and had insufficient documentation of why things had been done in the 1960s. With them out of storage, they were sending engineers to look over how things had been done as a jump start to the newest efforts.

The thing I liked most about Huntsville?

I like going through the phone books of cities to see how decadent they are, how many lawyers they need, and how many hobby shops they have, and other trivia.

Huntsville had a section for Rocket Engineer. Just one entry, but more than I have noticed in any other city.

**At the time I was looking at a foil actuator.

 

[Sparweb]

Last time I went to Cape C, I walked through the rocket garden and was mostly depressed by the sorry state of the displays... then saw the newly-restored Titan II gleaming in the sun.
Fell in love all over again.

Back to the "boneyards" subject. There are indeed big boneyards in the desert with 100's or even 1000's of airframes parked... Sometimes you can find aircraft wrecks behind the back doors of various local MRO's, sheet-metal shops, wrecking yards, etc... There are several in and around my city, and I doubt this city's unique. I was once in a rural area quonset building with 20 smashed helicopters in it. These were airframes retired from service by a sudden encounter with a planet, so to speak. It's not likely that any stranger off the street can just ask to visit for the fun of it, since there's a business to be run there, and probably a chain-link fence around the area, but if you ever do have the chance, don't turn up your nose. There is NO BETTER way to learn first-hand the meaning of "crashworthiness" than to carefully examine an aircraft wreck.


STF

 

[berkshire]

Gann.
Another source of information is to look at the FAA airworthiness directives, there you will find reports of cracks in parts, pieces that fail in service due to unexpected wear , things that chafe due to improper bracketing , and the corrective actions such as inspections or parts replacements that are required to fix these problems.
B.E.

You are judged not by what you know, but by what you can do.

 

[tbuelna]

I spent some time working at Boeing Renton in the structures group on the 737-NG program. Every piece of structure, including simple brackets, were designed in a very specific way that the company had developed over time. This approach ensured every part was optimized in terms of cost, weight, reliability, etc. based on the collective experience of the company's engineering staff. Your engineering lead would give you guidance on how a particular piece of structure should be designed. And your "simple bracket" design would be reviewed by over a dozen specialists before it was released for manufacture.

In short, every aircraft OEM wants things designed in a certain way. They'll let you know how they want their components designed when you go to work for them.