Stress Reports for structural DERs 3

[robbw]

This is for all the structural DERs and the like. What type of stress reports do you require (or create) before approving data via an 8110-3? Is one mandatory? or is it judged on a case-by-case basis, depending on need? How do you find strength data on vendor fastners/attachments/inserts/rivets etc. that are not covered under military standards? Must a copy of this stress report be supplied to the FAA when you send your copy of the 8110-3, etc.? What software is useful? Is there a site with sample stress reports I can examine?

Thanks for putting up with my questions.

Regards,
Robb

 

[joekm]

Well, technically, a stress report is not required. On the form is a statement to the effect of "attach additional sheets as required" for adding add any additional data to make the compliance finding. So, it is possible to do everything you need to do on the 8110-3 itself and whatever attached sheets you need.

However, it's a lot more practical to do a formal analysis and reference that on the 8110-3. It's easier for you to keep track of as far as document history is concerned and it's a lot easier on the FAA as well. As for report format, best advice I can give is to look at what other people have done.

Reports and documentation usually go to the FAA as part of an STC package, etc. and your FAA advisor is going to want copies of what you did anyways.

As far as data for unusual fastners, etc. Often times your customer will get it for you (and you file that away somewhere in case you need it later). Other times, you may be able to at least get a conservative estimate based on the info you do have. Internet and finding it by dumb luck also play a factor. Over time, you'll develop you own personal library of data for aircraft, hardware, etc.

--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[Heckler]

I did a computer equipment rack modification for a 747-200 and the DER required a full analysis report showing compliance to crash safety FAR. We were able to show compiance by structural calculation and by destructive testing.

One thing that stands out in your request is using nonstandard hardware. I would be extremely careful using unverified hardware sources. That could came back and cause major liability problems. I personally used Mil-HDBK-5 for all of my data sources on hardware.

I wish you best of luck. I you need an example of a report just let me know I will send you mine. cheers

Vince

 

[robbw]

Thank you Joseph and Vince, much appreciated.

Joseph: You mentioned to look at what other people have done (regarding stress reports). Is there a good source of sample reports online that you know of that I can peruse?

Vince: I'd be very interested in seeing a sample report of yours. You can send it to will2@boringmail.com - thanks.

To everyone else, I'd love to have some more input!

Regards,
Robb

 

[crackman]

Robb

The quality and content level of the report required depends on the program it is being submitted for. Part 21 (both in the regulations and in AC, Orders, and policy letters) do stipulate some level of content for specific programs in support of Type Certification, STCs, PMAs, ect. For 337 type repairs applicable to only one aircraft serial number, its generally left to the DER and what his FAA advisor expects. Although its always a good practice to document it with a report number so that it is easier to maintain. (remember, DERs are responsible for maintaining all design data for their approvals)

For large projects on multiple aircraft such as STCs, the reports generally need to contain the reference loads used, internal loads and freebody, allowables, and minimum margins of safety calculations. In addition, the FAA is more often requiring proof tests with strain surveys to include correlations to the analysis. As for allowables, that is getting to be a bigger deal every day particularly when dealing in cabin interiors (ie inserts, potting, etc.). FAA is requiring more validation of materials. Mil-Hndbk 5 and 17 of course are still acceptable but not very useful with cabin interiors.

James Burd
FAA DER - Structures/Damage Tolerance

 

[joekm]

Just to follow up a little bit.

As for unusual hardware, a fitting factor is required whenever the strength is uncertain or otherwise subject to variation. Even when you have well documented data including statistical reductions and all that stuff the FAA wants to see, odds are, you don't know the installation process as well. This is especially true for potted inserts or rivets and even bolt-and-nutplate. So, what I'm trying to say is, even if your fastener is well documented in MMPDS-01, you still need a fitting factor.

As for a document style, let me see if I can "sterilize" a general format that I've used (yank any proprietary refs, etc). Just bear in mind that it's just *a* way of doing it, the *the* way. You can find my e-mail by following the link in my sig file.

--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[bubb375]

Robb-

Good sources of information on fasteners and allowables should be found in the SRM for the aircraft. Also, liaison design handbooks should give you general guidelines for good design and substantiation.

Brian

 

[Sparweb]

My preferred way of dealing with fasteners not covered in MMPDS or Mil-Hdbk-5, or a peculiar joint of whatever configuration, is by performing a load test. For the one-off mods that I typically do, it's the simplest way to demonstrate that the structure is sound. Even for welded structures, which are easy to analyse (particularly with some of the free FEA packages out there), I prefer to test. Fitting factors don't apply to structures that have been tested, either.



Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[crackman]

Hi Guys

Just wanted to let you know that after much searching in my large but very disorganized library I finally found the FAA references I was thinking of with respect to acceptable FAA stress reports.

Back in the old old days before the ratio of lawyers to engineers exceeded infinity, the FAA and industry had no problem stipulating very detailed requirements for certification.

If any of you can locate an old CAM 04 (civil aeronautics manual)for Airplane Airworthiness manual dated around WW2 (my original copy is dated July 1, 1944) you will find a very detailed section under Part 04.032 entitled "Data required for type certificate". This section gives a 2 page detail of what both drawings and drawing lists should contain and then has individual detailed paragraphs on criteria for the following reports: weight and balance, structural reports, structural analysis, test reports, etc.

In addition, the section on Proof of Structure Part 04.3 is 26 pages in length detailing how compliance is shown, acceptable analytical methods, test loads, test procedures, etc. You will never see this detail today unfortunately due to the sheer size of the governments legal branch reviewing anything and everything that is published by the FAA.

Although CAM 4 is old, it is not invalid for many of the old aircraft. Just remember the Cessna 172 TC goes all the way back to CAR 3 November 1, 1949!!!!

The old CAMs and CARs are very good references for any DER to understand how the current regulations came about. Current FARs are purposefully kept very short and to the point but do not explain the history and experience behind the rules. Another good place to understand FAA requirements are the published FAR Amendments in the Federal Registry.

Good luck

James Burd
FAA DER - Structures/Damage Tolerance

 

[Sparweb]

Those were the days when the reg's themselves stated "...It is not intended that the "paper work" be overemphasized to the detriment of the practical results, and it should be reduced to a minimum for small airplanes..." (Ref. CAM 4b.16, 1960). A bygone era.

When CAM 4b was converted into FAR 25, some parts got moved to FAR 21. What's left is 21.303.

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/MainFrame?OpenFrameSet

Crackman, when I look in my copies of CAM 4b/4a, there's no part 04.032. What's the date on your copy?

Anybody who wants to explore these old documents should go to:

http://dotlibrary.specialcollection.net/

Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[crackman]

Sparweb

Oh you right you are. Unfortunately the hey days of aviation are truly gone.

My copy of CAM 4 is dated 1944. Go to your link on the dotlibrary and look under CAM 4 (not 4a or 4b, these are regs, CAM 4 are the guidelines). I believe 04.032 was first introduced in the online 1941 version. Its the second CAM 4 on the dotlibrary listing.

Let me know if you manage to find it.

James Burd
FAA DER - Structures/Damage Tolerance

 

[Sparweb]

We rely on the "original basis of certification for many types that we work on (Beech and De Havilland twins, and Bell heli's, for example). Using these old reg's keeps projects from spiralling.

It didn't take me long to find the section you're talking about, although the one I got is dated 1941. Regardless, these old documents often have handy little tidbits of info that have disappeared from the current reg's. Ensuring that the info is still applicable is another matter.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout