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,

 

[ewh]

That would have to be worked out relative to the stresses expected at that joint.

 

[rb1957]

industry standard edge distance is 2D, measured from the center of the hole. i use 2D+0.05" to allow some tolerance on installation. i use the shank diameter (and not the CSK diameter). this can be relaxed if there isn't a large load applied normal to the edge (if most of the load is applied parallel to the edge; 1.5D would be a minimum (for sheet metal structure).

Lugs are different and typically have smaller ED.

 

[AminG]

I recall using a distance of 2 times the diameter for the edge distance. This was a general rule used to check design.

 

[SWComposites]

The general standard in the industry for metals parts is 2D + 0.05"; For composite parts it is 2.5D + 0.05".

 

[berkshire]

When you start thinking about creeping closer to the edge on edge distances, start thinking about the De Havilland Comet.
B.E.

 

[mrcadman2u]

Thanks guys. I appreciate the help. I know that at Boeing I think we used 2D + .062 and composites 2.5D +062 same as SWComosites pointed out. The reason for the question was that someone here said that there was an Industry standard out there that could be referenced. I was not sure so I went to the experts.

Thanks again,

Jerry

 

[WhiteRabbit]

This seems to be more company driven but it is mostly the same.

2D+.050 is the current Boeing standard for design. Way back when it was 1.7D for load running parallel to the edge if no buckling occurs. I do routinely see 1.5D on older designs from the 50 to mid 60's designs.

If I recall correctly Douglas used 2D+.030 regardless of load direction.

Liaison Engineering will routinely drop it to 2D because most of the material fastener allowables are taken from 2D. But this should not be a good rule of thumb for design practices. Some of the bearing allowables are higher than a 2D material shear out allowable.

 

[diamondjim]

VDI 2230?

 

[berkshire]

WhiteRabbit (Aerospace)
1.5D used to be the standard edge distance for metals in the 1950s.
Following the Comet disasters, it was changed in Great Britain to a minimum of 2D. I believe most other aircraft manufacturers followed suit.
B.E.

 

[WKTaylor]

Guys...

MIL-HDBK-5 [MMPDS] allowables for most metals show FBru & FBry in terms of 2.0 (= 2D edge margin) and 1.5 (= 1.5D edge margin) ... see for Yourself... the differences in bearing-tear-out/yield allowables are significant!

The classic "2D +(factor)" equation insures a minimum 2D edge spacing for the nominal diameter fastener... and some accounting for AT LEAST the 2nd oversize (0.032) repair fastener... plus some typical maufacturing "wiggle-room". Typically the "factor" is 0.050 or 0.060... although I have see as littles as 0.030.

Note: on some old Boeing military Acft, an edge margin of 1.7D + 0.030-0.06" was routinely used in design. In-real-world practice, this often drifted down to 1.7D for typical production installation tolerances. Repairs with a starting 1.7D fastener egde margin, really get dicy for the liaison and stress guys when oversized fasteners are required... and gets even worse with thin-skins and deep-countersinks!

My preference is definitely 2D + 0.06"!!!

Regards, Wil Taylor

 

[planedr]

2D edge margin is fine pretty much across the board.

The Comet was way more than just EM.

Bear in mind though that Boeing being the rebels they are have the same definition for edge Margin (EM) as everyone else in industry uses for edge Distance (ED).

Boeing uses a tolerance of plus minus 0.030" for production. So a worst case you have 1.7EM which would drive a repair on existing structure to say 1.5EM min. I have routinely had Boeing approve as low as 1.5EM on structure, skins 1.7EM.

Now the allowables in MMPDS are great. It is my experience that statically it is not an issue, of course depending on all the appropriate caveats. It is the fatigue portion. at 2D the run out is nearly infinite at 1.7 it is exponential and at 1.5 it is worth review. With special procedures for hole quality, zero timing, inspections, life limits, 1.2 can be fine.

If you are so close statically the EM is an issue you won't cut it for fatigue.

 

[rerig]

Careful.
There is a difference between Edge Margin and Edge Distance.

Interestingly enough, Boeing has messed this up with the integration of Douglas products.
Examples are the DC-9/MD-80 SRM and the 737 SRM definitions of Edge Distance vs Edge Margin. The figure is almost identical, but the description of the measurement is Opposite. This brought a "UHHH, we'll get back to you" response from Boring Tech Support after a Repair Submission was disapproved for short ED.
Old Douglas Engineer submitting to Boeing Engineering.

I know what you mean. But have seen both terms used here.
Even in the ar-mmpds-01 manual both terms are used without an explaination of exactly where the dimension is measured.
Assumed all measurement from the center of the fastener location. (or am I still confused?)

Rerig

 

[rb1957]

you're correct, edge distance is measured from the hole CL.

edge margin ?

 

[whalesA3D]

I am the old Douglas goat that submitted a repair to Boeing ESE that my partner rerig mentioned above. When I deal with the engineers that reside in the hallowed halls on top of "Mount Boeing" I use their engineering terminology as a profesional courtesy. I used edge margin of 1.5 measured from the edge of the hole to E.O.P. in my repair scheme. After the usual 5 day wait they sent me a responce that my E.M. of 1.5 was unacceptable, and I was to use an E.M. of 2.0. I looked in Chp 51 in the SRM and sure enough E.M. had been changed from 1.5 to 2.0 and now measured from the center of the hole. When did this change occur? Well shame on me for not checking the SRM (my goof) I was even more surprised when I looked at my trusty (and current) DC-9/MD-80 SRM and found 2.0 ED measured from the center of the as it has always been done. I copied both documents to .pdf file and sent to ESE. Rerig accuratly described the response. So currently Boeing North uses 2.0 EM measured from the center of the hole and calls ED the distance from the edge of the hole to EOP. Boeing South uses 2.0 ED measured from the center of the hole and call EM the distance from the edge of the hole to the EOP. Yep, same company. I'm not trying to kick Boeing in the knees, but for a company that prides itself in engineering excellance and lets you know about it every time they get the chance........What the heck?

 

[rb1957]

whales ... aim higher (with your kick !)

 

[epeus]

Bombardier Strength Manual States:

Protruding head

Edge margins - minimum 1½ (fastener dia)
preferred 2 (fastener dia)

Countersunk head

Edge margins - minimum 2 (fastener dia)
preferred 2½ (fastener dia)


" and e is the edge distance measured from the hole centre to the edge of the material in the direction of applied stress."

As pointed out previously there is no definition for 'edge margin' in this manual.

IMHO Fastener edge distance / margin is a fairly basic thing, this should be exceptionally clear-cut across aircraft industries and countries!

 

[Sparweb]

How about a Mil spec for your reference? It's MIL-R-47196, "RIVETS, BUCK TYPE, PREPARATION FOR AND INSTALLATION OF (Superseded by NASM47196)", available from the ASSIST website. A very convenient thing to call up on a drawing - I suspect that's the purpose of Mrcadman2u's question.

Edge distances and terminology are spelled out in detail in the spec, and it's public domain. It is interesting to note that even in the standard, the allowable "edge margins", as they call them, are also subjective. The allowable margins are different depending on rivet head type, dimpling, and inspectability. Since the document dates from 1977, my guess is that the authors could have drawn from many sources, whose data had been refined over many years.

Mind you, there is a passage that goes something like: "edge margins less than those specified above requires further engineering approval", which is sorta what everyone else here is talking about.

There may also be guidance in Advisory Circular AC65-12, though I haven't got a copy handy to look it up. There is a very large and comprehensive section about riveting.

In any event, if one is going to specify a <2D edge distance, one will be venturing into the "non-standard" territory, as everyone has already pointed out.



Steven Fahey, CET

 

[rb1957]

sparweb,

AC65 12 is "[Large AC] Airframe and Powerplant Mechanics Powerplant Handbook" ... is that the one you meant ?

maybe AC43 13-1, chapter 4, section 4 ... there is a small paragraph on ed, in a nice section on riveting ("all you wanted to know ...")

 

[rb1957]

to follow up on sparweb's mil spec ... (geez isn't ASSIST a fantastic source of data) ... you have to download the superceded MIL-R-47196, as you have to buy the NASM-47196 from the AIAA.

and not to bash Bombardier, but does anyone else consider the CSK in edge distance ? ... it's an interesting statement as i'm sure (from personal knowledge) that all previous designs would have used 2D. doesn't it create liability issues ? and does "minimum" mean that you spec 2D and buy-off 1.5D ?