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Does edge distance change

klovning

Well Known Member
Does reccomended edge distance change on aluminum depending on the thickness?

I understand it is preferred to have 1/4 in edge distance on most everything, but I'm under the impression that the tear out strength, and the propensity to crack on a 0.016 piece and a 0.063 piece of Alclad would be drastically diffrent for that same 1/4 inch and the same 4- rivet.

The reason I ask - I buggered a 4- rivet hole a wee bit (ovaled it with the countersink drillbit). It's on a slightly large, and therefore expensive and difficult to ship, piece.

I have some 5- rivets - I am thinking of over drilling and then bucking the larger rivet in the exact same place. There would still be a 7/32 or so distance edge of drill hole to edge of piece. (do you measure from the the center of the drill hole or the edge?)

I dont think this would be a huge faux pas as there are 4 other 4- rivets in proximity holding the pieces together.

Any opinions welcome.
 
Edge Distance

I will avoid going into all the theory behind the shear stresses involved in joining thin materials--mainly because engineering school was a loooong time ago :D. The simple answer is that you want to leave a distance between the center of a rivet and an edge equal to two times the rivet diameter. If you have a 1/8" rivet, then you should have 1/4" between the hole center and the edge. That's a brief summary of what's in the Aircraft Inspection and Repair AC 43.13-1B manual.

And while you're correct that a thicker material isn't as likely to tear out, there were likely larger stresses associated with that part to necessitate it being thicker. So the 2x diameter distance still holds.

In general, one "questionable" rivet won't make the plane fall apart in your garage, as there are many rivets to share the load. I can't see the part you're working on, but the tech help guys at Van's are pretty good about answering questions like this. Most builders direct a lot of questions to Van's early on, but the questions taper off as we gain experience and knowledge.

If you're in doubt and it still nags at you, err on the side of safety and replace the part. I think I can safely say that every builder out there has had to order replacement parts from Van's, so there's no shame in that.
 
Edge Margin

Dave Welsh?s answer is right on and covers the essence of edge margin. Buying a new part isn?t the only solution. A doubler spread out over 3 ? 4 rivets (edge margins correct) will work also. Function is primary but form is also an issue which can be addressed when finances are an issue.
Cheers and onward.
 
Will existing rivet spacing allow adding additional rivet(s) to the side of the problem rivet? If so, that might allow continuing with the existing part.

Charlie
 
Edged distance is very important as the aircraft ages and you have to do a repair or replace bad installed rivets. Below is what AC 43.13-1B states:

Rivet edge distance is defined as the distance from the center of the rivet hole to the nearest edge of the sheet. Rivet spacing is the distance from the center of the rivet hole to the center of the adjacent rivet hole.

For single row rivets, the edge distance should not be less than 2 times the diameter of the rivet and spacing should not be less than 3 times the diameter of the rivet.

Reference AC 43-13.1b Chapter 4, Paragraph 4-57(c).
 
Thanks guys - as always this forum is a wealth of experience and info.

I ordered replacement parts yesterday for the small stuff and for the one the larger piece I ordered a sheet of alcad from AS. I'll use the original as a template and just cut myself a new one, leaving more distance at the edge near the critical point.
 
Just for fun; take a look at you wing spars, specifically the 7/16 holes for the close tolerance bolts, they are something under 1.5 times dia. in edge distance.:eek:

I agree that if one rivet in a row is off, it's not a big deal. I have an old 8 kit and the floor ribs are made so you can't get the proper edge distances on both ends, no matter what. Van's told me that it's normal for that kit and not to worry about it. :rolleyes:
 
Yes, you'll see some rivet lines here and there with less than the normal 2X edge distance. The 2X spec assumes a load vector perpendicular to the rivet line; the problem is both tear-out and material distortion due to the mechanics of a single-lap joint. If the load vector is parallel to the rivet line a designer might choose less edge distance; the joint mechanics are entirely different.
 
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