Aircraft edge distance
Aircraft edge distance
(OP)
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,
Thanks,
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RE: Aircraft edge distance
RE: Aircraft edge distance
Lugs are different and typically have smaller ED.
RE: Aircraft edge distance
RE: Aircraft edge distance
RE: Aircraft edge distance
B.E.
RE: Aircraft edge distance
Thanks again,
Jerry
RE: Aircraft edge distance
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.
RE: Aircraft edge distance
RE: Aircraft edge distance
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.
RE: Aircraft edge distance
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
RE: Aircraft edge distance
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.
RE: Aircraft edge distance
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
RE: Aircraft edge distance
edge margin ?
RE: Aircraft edge distance
RE: Aircraft edge distance
RE: Aircraft edge distance
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!
RE: Aircraft edge distance
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
RE: Aircraft edge distance
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 ...")
RE: Aircraft edge distance
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 ?
RE: Aircraft edge distance
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?
RE: Aircraft edge distance
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
RE: Aircraft edge distance
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.
RE: Aircraft edge distance
RE: Aircraft edge distance
"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
RE: Aircraft edge distance
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).
RE: Aircraft edge distance
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.
RE: Aircraft edge distance
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
RE: Aircraft edge distance
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.