McDonnell Douglas Structural Design Manual V2

[Venator]

Hello everyone, I was recently comparing different models of crippling and came across the McDonnell Douglas Structural Design Manual V1. In section B6.5.2.1, there is a graph for determining the crippling stresses of extruded profiles, which coincides in most cases with the Gerard and Anderson model. But in the same paragraph there is a reference to the second volume of the manual or section E for rolled profiles.
Question, does anyone have the second volume or could someone share a graph or methodology for calculating the rolled profiles?
Thank you all and good luck

 

[Sparweb]

I checked my library, and I only have Vol. 1. Sorry.
Can I assume you do have Bruhn, which covers crippling of formed profiles?
The references at the end of chapter C7 offers more leads. Many could be hard to find by now.

 

[Venator]

Bruhn's book proposes the Needham and Gerard method. The method given in McDonnell's manual is similar to the version proposed by McCombs in the appendix to Bruhn's book, down to the sign of the coefficients. However, it is noted that it is only suitable for extruded profiles, and for rolled profiles, part 2 is needed, which unfortunately is not available from any colleagues or libraries. McCombs also suggests using this method for rolled profiles, which surprises me.
Perhaps the difference between these approaches is small, so we can ignore the difference, but this is the question that worries me

 

[SWComposites]

The Boeing BDM-6220 has metal crippling curves for formed and extruded sections, if you have access to that. The curves look similar but not exactly the same, as the extruded sections benefit from the fillet radii in the corners.

 

[WKTaylor]

McDonnell Douglas Structural Design Manual V1... looking for V2?? MAC/DAC and Boeing manuals/documents all have 'document numbers'... what are they and which-one(s) are You looking for?

Hmmmmm... seems like You are using proprietary data already... so ask MDC/Boeing... if You have authorized access.

/NOTE1/ A little secret I discovered years ago is that NACA did most of the early theory/testing/val/ver for what would become the roots for design/analysis manuals in most every company... that eventually grew/diverged with 'experience' over time... so there is 'striking similarity' across early manuals. The on-line NACA library may also provide 'insight' thru related documents.

/NOTE2/ While working many civil/MIL Acft over the years, I too accumulated a shelf full of proprietary design/analysis manuals, which I hold 'close-at-hand'. Some are for companies that no-longer exist or have merged... But proprietary data remains proprietary. Be careful.

Regards, Wil Taylor
o Trust - But Verify!
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", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[Venator]

The first part of the report has the number DAC 25-2066 (3-71), unfortunately, in all the sources available to me the second part is referred to simply as the second part without a number.
The Boeing employees with whom I spoke on this issue also referred me to the BDM and had only the first part of the report available. This seems strange to me. I read NASA and NACA reports, and they have slightly different curves. And the curve from the first part is more similar to the one that McCombs cites in the appendix to Bruhn. By the way, it is interesting that McCombs does not cite the source from which he took it.

 

[rb1957]

Apologies, but we're spilling a lot of ink over a very tiny issue, IMHO.

Are you doing a static test, then that'll prove the point.
Do you have a small margin, so a test failure is possible ?
If you feel like you Have to Know ... then do a test yourself. You've tried to find the references and to no avail.
Or if you feel that without this data you can't be sure of the strength of formed sections, then don't use formed sections, use extrusions.

"Wir hoffen, dass dieses Mal alles gut gehen wird!"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[LiftDivergence]

Hi, I have the manual Volume II you are looking for, it is the same number DAC 25-2066 (3-71).

There are curves for formed sections if you are searching for "compression panel allowables" which I assume you are based on your reference to Volume I B6.5.2.1.

Unfortunately I have no idea what the proprietary nature of this data is or if I can share it.

However, there are many ways to skin this cat, so to speak, and many references.

I would personally recommend "Theory and Analysis of Flight Structures" by Robert M. Rivello, Chapter 16 covers instability and curves for thin walled columns that are formed sections. He references:

van der Mass, C.J.,"Charts for the Calculations of the Critical Compressive Stress for Local Stability of Columns with Hat Sections"
Needham, R.A., "The Ultimate Strength of aluminum alloy formed structural shapes in compression"
Among many others

Usually the way to handle compressive failure of formed (or extruded) thin-walled sections is to break them up into segments and treat the total section using Needham's method which is presented in many structural repair courses. You can find a description of that in Aircraft Structures by David Peery, Section 14.14. If you are concerned about the constants / exponents to use for formed vs extruded segments, Boeing repair design course notes, which are not proprietary, and other sources, have those.

You can look through the NTRS for the handbook of structural stability and many other references.

Can anyone can advise on the proprietary nature of the manual??

Keep em' Flying
//Fight Corrosion!

 

[WKTaylor]

Rb...


Hmmm... I guess some of our discussions are getting to be '...fairy's on the the head of pin'?

Regards, Wil Taylor
o Trust - But Verify!
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", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[LiftDivergence]

I should note that superimposed on all of the charts in Section E is the following statement:

"NOTE: CURVE DETERMINED BY A SEMI-EMPIRICAL METHOD WHICH ASSUMES THAT THE BUCKLING STRENGTH OF THE VARIOUS PLATE ELEMENTS CAN BE ADDED TOGETHER TO OBTAIN THE ULTIMATE STRENGTH OF THE ENTIRE SECTION. THERE IS SOME EVIDENCE INDICATED THAT FOR ONE EDGE FREE WITH A B/T > 12 THIS MAY BE CONSERVATIVE."

If I had to make an educated guess, I would say all McDonnell Douglas did to generate those figures was use Needham / Gerard method from NACA TN 3784 to draw out the curves for different materials.


Keep em' Flying
//Fight Corrosion!

 

[Venator]

As far as I know, there are no distribution restrictions in the file, but you know best, I'm going by the first part. Could you provide a part of the file or a link where it is possible to do so, under the rights of fair use for educational purposes? I'm not from the United States so I can't be sure about the legal norms in this country.
Thank you for explaining the notes to the graphs in section E. I am only interested in comparing them to the well-known Needham, Gerard, Anderson graphs.