Liaison Engineer Referece Texts & Repair Question

[koopas]

Hello all,

Last week, I got a hold of both of Michael Niu's books on stress analysis and structural design. Someone suggested to me Jean Claude Flabel's Practical Stress Analysis for Engineers. Can you recommend this book? I've read fairly positive reviews. Another classic which I've only come to know about is Roark's Stress & Strain book. Would that text help the airline engineer at all?

What would be nice: a layman's text explaining the SRM! Something entitled "SRM: secrets revealed". Frankly, I am having difficulties looking things up in the SRM. For instance, the other day, I wanted to know the acceptability/requirements/parameters required to cold work an angle that held the cargo door seal depressor to the cargo door frame. I couldn't find anything in the SRM on the subject. The angle didn't seem dented too badly but my lack of experience made me reluctant to give the go ahead to cold work it. In the end, I called out for a dye-pen. or eddy current inspection for cracks after the cold-work, and alodine/prime/paint...as a temporary repair (replacement of angle at "A" check).

My lack of experience certainly stood out that day. Mechanics were expecting my repair order but I was fumbling to research data while the plane sat at the gate. I wished there could be a resource (text, web site) for common sense aircraft information used by liaison engineers without the drawn-out nature of the SRM. I find the latter a little dry...and the information hard to locate. Even when I do locate the information, some of it is obscure.

I am sure one of the other experienced structures guys could have guided me that day but I was the only one. So let me ask you this...what are the limitations of cold-working metals? When can you do it and when can't you? What should you look for when cold-working metals? The angle is attached via rivets to both structures.

1. I looked on the myboeingfleet.com drawing and i couldn't find the angle material. I digged up a Boeing structures training manual (which I find more "user friendly" than the SRM) which directed me to

1.1 cadnium plate if it was steel, then alodine/prime/paint

or

1.2 adodize if it was aluminum, then alodine/prime/paint

since I didn't know the material, I only called out the alodine/prime/paint part. I realize that 2024 is more maleable than 7075 when cold-worked, correct? Would you have called out for dye-pen or eddy-current crack inspection? Is the only difference that you have to strip the paint to dye-pen?

Anyway, what would you have done differently? What did I do wrong and what did I do right? ARRGHHH! Sorry for all the scatered questions...feel free to include your replies in my original text. Thanks.

Young frustrated engineer.

 

[avio]

Hello,
don't be frustrated; it is a good point that your are reluctant instead of going forward without well understanding what you are doing.
Personally, I have little experience with coldworking of Aluminium. Do you have access to the ASM handbooks? They have a complete volume dedicated to Aluminium; check

http://www.asminternational.org

Good luck

 

[johnfalky]

Depending on what type of A/C you're working on, lets assume that it is a Boeing, and that it is a standard cargo door, i.e. part of the original design. As far as I can tell Boeing has instructions for the repair of the Seal Depressors in the manual. Some cold working is allowed, using approved Boeing data. Other data might have some cold working allowables, but the data might not be approved for use on your aircraft. If the seal depressor is severely dented, cold working it back into shape might NOT be the way to go... and what about the structure that the seal depressor is attached to?
If it is an aftermarket Cargo Door, often found as "freighter conversions", you cannot use the SRM for the repair unless you have FAA-approved documentation stating that such instructions may be used.

 

[alexeu]

Sheet metal or extrusions of parts may be cold-formed in any temper but preferabably in -W condition or -O condition. This is covered under SRM 51-30-01 which refers you back to BAC 5300 (forming and straightening of mettalic alloys). If formed in -W or -O condition, the part has to go thru a heat treat cycle. Dye-pen and HFEC after cold forming is recommended.

Flabel's Practical Stress Analysis for Engineers is a good beginning for any Engineer. The theory is well applied and good illustration of problems. Although the contents is not as extensive as Bruhn. or Michael Niu.

I do not suggest Roarks's unless you are interested in stress analysis. It has all the formulaes compiled in one book for quick reference.

Cold working metals look for CRACKS!!

I think you are wrong in quoting the Boeing Structures Training Manual.

Item 1: You do not Cadmium plate and then alodine steel. Besides, there are options to passivate steel in lieu of cadmium plating. Cadmium plating itself is a protective cover and do not require further treatment besides prime and paint for additional protection.

Item 2: You do not anozide aluminum and then alodine aluminum. BMT group would probably be better in answering this question. But I gather that alodine is common in repair station in lieu of anodize.

Most of the details can be cross-reference to SOPM, if you have one handy in your office. By the way, which airline are you working with?

Rgds
Aeu

 

[l871057]

Hi, gentlemen,

I am working in the field of liaison engineering of aircraft company. The three books what you hold are helpful for your job and those are like bible for engineer.
1. 2024 is more portion of strength than 7075. but 7075 is
good for fracture toughness point.
2. In the light of my experience, the material can be cold
form with following fluorescent penetrant inspection or
eddy-current-inspection. I believe that your judgement
is proper at leasst. If the angle can be disassembled
from assembly, it is better to cold form. The best method
forming the angle is to anneal or quenching.
3. It is not allowd to apply cadmium plating to aluminum,
but steel alloy. You should have ordered alodine (brush
chemical film) and primer, paint over the repaired area.
Anodize for aluminum alloy can not be applied in the
field, if the proper solution and tank do not prepare
in proper area. But, alodine can be coated in place of
anodize.
The passivation id for stainless steel (CRES).

Should you have any question, please contact me

 

[koopas]

l871057,

Thanks for replying to my post. I've got a few more questions.

In the #2 reply, you say that "the best method forming the angle is to anneal or quenching". What do you mean by that? The angle was cold-formed with some sort of mallet or hammer.

Could you clafify what you meant in reply #3 regarding anodizing aluminum?

Also, what is meant by "passivate" steel?

Thanks
Alex

 

[davida3d]

Mr Koopas,

Maybe I can help. The SRM is frustrating for sure, But usually 99% of the information is there if you know where to look. What I do in diagnosing a repair is this:

1. Look at damaged part and go to Material I.D. section (i.e.) Wing (chp 57). Go to Chp 57 Index to find Chp/page number of part you are working on. Look at picture to get Material I.D. Info. Extrusions are listed by P/N in Chp 51.

2. Go back to Chp 57 index and proceed to developed repair section, see if there is a OEM repair for the affected part. If not........

3. Develop repair using Info obtained.

I found your cold working information in 737-200 SRM
51-30-9 and in DC-9/MD-80 SRM 51-30-9. Also alot of valuable process information can be found in the Aircraft OHM/CMM Chp 20. Plating, Machining, Repair Bushings Etc. For the DC-8 it is Chp 13 in the OHM. I see alot of Liason Folks sitting for hours in front of the Tape Reader looking for what can be found in minutes. The secret is using the the index. Your last Question, Passivation is a Chemical Cleaning process leaving an oxidized surface when finished. It is an excellent Corrosion Preventive Treatment for Steel. Read DPS 9.07 (Douglas Process Specification)

If you ever get a moment of spare time, copy the index of each Aircraft You work with for a desk reference. Douglas and Boeing Process Specs are good reading also.
I hope I have been helpful.

Best Regards,

David
------------------------------------------------------------
Someone needs to Saint Donald Douglas,
Thank God for the Finger Doubler.