Aircraft edge distance 12

[mrcadman2u]

I am looking for an Industry standard that calls out the edge distance of fasteners. I was wondering if there is anyone out there who may know of the spec?

Thanks,

 

[diamondjim]

Have any of you seen or used VDI 2230?
It may be much more than you want to read
but they do have recommendations for edge
distance depending on the thickness of the
material. I think margin by definition
would mean the material from the od of the
hole or c'sink to the edge of the material.
The spec uses edge distance and is from the
center of the hole to the edge. I have not
seen margin used for a long time.
If edge distance is 2 times the diameter, then
margin would be 2 minus 1/2 the diameter of the
hole which would be 1.5 times the diameter.
Interesting. Are these specs a carry over from
riveting specs?

 

[Sparweb]

Oops, AC65-15, not -12. They are parts of a series of mechanic's handbooks. Download from the Advisory Circulars page on the FAA's website. Given their size and usefulness, I recommend getting the Jeppsen printed series.

It's of great value to know how the technician learned how to do it, and books like these are often the basis for their training (ought to be, anyway). Like the cartoon in Bruhn asks, "Who determines the strength of a bolt?"

Steven Fahey, CET

 

[WhiteRabbit]

Something that is interesting that I found; Heritage Boeing is the only OEM that uses Edge Margin. Everyone else seems to use Edge Distance. Mil-HDBK-5 uses Edge Distance. Heritage Boeing used to call Edge Margin the distance of the center of the hole to EOP if the load was normal to the EM measurement. But somewhere it became the same as ED.

My opinion is that Boeing should follow the rest of industry. When I talk to Heritage Boeing I use EM but by force of habit I type ED in my repair orders and Boeing usually rejects it.

 

[StressTheGame]

From memory Douglas measures ED from the edge of the hole to the edge of the part where as Boeing defines it from the hole center line to the edge of the part. The reason 1.7D edge margin is routinely considered an acceptable rework configuration is because there is no degradation from a fatigue point of view for edge margins down to 1.7D (per data in Boeing's "Book 2 - Structural Fatigue Methods and Allowables"). The degradation experienced down to 1.5D is also minimal - specially when one considers rework to an old aircraft - oops, did I say that? However, when designing repairs (or new designs) one should allow for the ocassional boo-boo - thus 2D is standard. Also, like previously mentioned the application of load is critical to distinguish between edge margin or end margin effects regarding sheet metal. Boeing highlights differences between both in their "rework correction factors". A short end-margin affects the fatigue quality at the lead-fastener location - NOT at the fastener suffering from a short end-margin condition - unless if tearout becomes a concern .

 

[whalesA3D]

Quote from Above:
"From memory Douglas measures ED from the edge of the hole to the edge of the part."

I'm sorry to disagree with you, but Douglas has always measured E.D. from the center of the hole to the EOP. Boeing used to measure E.M. from the edge of the hole to the edge of the part. Boeing North now measures EM from the center of the hole to the EOP. Boeing South (Douglas) still measures E.D. from the center of the hole to the EOP I have current SRM's and archieved SRM's from both companies to back this up. I wish I could post the .pdf's I sent to Boeing about this subject here for a good laugh....their responce was so typical of being caught with ones pants down..."Duh, We'll have to get back with you on that"...Quote

 

[StressTheGame]

Hi whalesA3D!

Thanks for your input. I haven't worked @ Douglas; therefore, the info I quoted was hear-say. I appologize if inacurate .

I worked @ Boeing from 1984-1996 mostly as a 747 Stress Analyst. Throughout this period I am certain that Boeing's Definition of "Edge Margin" was from the center of the hole to the edge of part (Ref Boeing's D6-24957, Structural Design for Durability). I admit thou that I have used the terms "Edge Distance" and "Edge Margin" in rather loose ways throughout my career - as long as I knew where the measurement was taken from-to .

Since Boeing - Everett, I have worked with Hawker de Havilland (Sydney), Civil Aviation Safety Authority - Australia, and Royal Australian Airforce and I cannot remember (again memory is a tricky beast) many instances of people measuring edge margins (or edge distances) from edge of hole to edge of part.

You mention funny discrepancies in approach between Boeing and Douglas. Sometimes this extends to differences between Boeing Everett (747, 767, 777) and Boeing Renton (737, 757).

 

[planedr]

Gents,
I thought it was pretty clear on the 29th Boeing defines edge margin as the center of the hole to the edge of the parts, SRM 51, period.

Everybody else in industry defines that as edge distance. Again that's clear.

Who cares how they got there? You just need to be cognisant of it and your QA needs to be cognisant if you are working multiple manufacturers.

Refer to the standard aircraft workers manual that has been around as long as airplanes. Every A&P has (or should have) one Section 7 page 1. It is different than Boeing. However when working Boeing products SRM 51 RULES. As does every other manufacturesr SRM 51.

Just like fasteners you have to change your terminology and callouts to be appropriate to the manufacturer. If not you are contributing to a human factors problem.

 

[mrcadman2u]

Wow. This is a great discussion. I really appreciate everyone's input chimming in on this one. I did not think there was this much interest. That is what is great about this forum. It sure is good to see the varied disciplines.
I do have to agree that there are a lot of factors to come up with the proper edge distance and there does not appear to be catch all for all instances. You have to work with the strength and material guys to make sure the edge distance(margin)is correct for what you are trying to accomplish.
Again I appreciate everyone's input and lively discussion.

Jerry

 

[taoofeng]

I have been a structures engineer for 25 years, and the biggest arguments I ever had with Design was over edge margins. I wanted the 2D + .06 margin, but Design insisted that (a) it would add too much weight, (b) Boeing never did write this down as a requirement but only as a "suggestion", and (c) Design has it's own manual that has a table of edge margin vs thickness (with values that vary from 2.2D for thin parts down to 1.44D for thick parts).

Now I am with Spirit Aerospace, and am writing the stress manual that the company will be using for future projects. You can be sure that this time 2D+.06 is going to be written down in bold print.