![]() I worked Boeing from 1984-1996 mostly as a 747 Stress Analyst. I haven't worked Douglas therefore, the info I quoted was hear-say. ![]() RE: Aircraft edge distance whalesA3D (Aerospace) 16 May 06 13:47 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. Boeing highlights differences between both in their "rework correction factors". Also, like previously mentioned the application of load is critical to distinguish between edge margin or end margin effects regarding sheet metal. 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. 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"). Steven Fahey, CET RE: Aircraft edge distance rb1957 (Aerospace) 3 May 06 09:02įrom 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. 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. There is a very large and comprehensive section about riveting. There may also be guidance in Advisory Circular AC65-12, though I haven't got a copy handy to look it up. 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. 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. The allowable margins are different depending on rivet head type, dimpling, and inspectability. It is interesting to note that even in the standard, the allowable "edge margins", as they call them, are also subjective. A very convenient thing to call up on a drawing - I suspect that's the purpose of Mrcadman2u's question.Įdge distances and terminology are spelled out in detail in the spec, and it's public domain. 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. 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? RE: Aircraft edge distance rb1957 (Aerospace) 2 May 06 11:10 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. 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. 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. had been changed from 1.5 to 2.0 and now measured from the center of the hole. I looked in Chp 51 in the SRM and sure enough E.M. of 1.5 was unacceptable, and I was to use an E.M. After the usual 5 day wait they sent me a responce that my E.M. I used edge margin of 1.5 measured from the edge of the hole to E.O.P. 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 am the old Douglas goat that submitted a repair to Boeing ESE that my partner rerig mentioned above. Regards, Wil Taylor RE: Aircraft edge distance My preference is definitely 2D + 0.06"!!! and gets even worse with thin-skins and deep-countersinks! Repairs with a starting 1.7D fastener egde margin, really get dicy for the liaison and stress guys when oversized fasteners are required. In-real-world practice, this often drifted down to 1.7D for typical production installation tolerances. Note: on some old Boeing military Acft, an edge margin of 1.7D + 0.030-0.06" was routinely used in design. Typically the "factor" is 0.050 or 0.060. plus some typical maufacturing "wiggle-room". and some accounting for AT LEAST the 2nd oversize (0.032) repair fastener. The classic "2D +(factor)" equation insures a minimum 2D edge spacing for the nominal diameter fastener. the differences in bearing-tear-out/yield allowables are significant! MIL-HDBK-5 allowables for most metals show FBru & FBry in terms of 2.0 (= 2D edge margin) and 1.5 (= 1.5D edge margin).
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