I managed to get out to the shop tonight since the rain was less threatening than yesterday. The goal for tonight was to get the rivet layout drawn, holes drilled, and the part trimmed to final dimensions. As I was doing the rivet layout something caused me to pause and go back to AC 43.13 to review something. The original plan was to space the AN470 rivets using a 2D edge distance and a 4D between rivet distance. This seemed a bit wide tome as I looked at that pattern drawn on the part. In AC 43.13 on page 4-26 is a section for Wing and tail surface ribs in paragraph 4-58 (c). It then refers to two figures, 4-13 and 4-14, on pages 4-29 and 4-30 respectively.
The epiphany that I had that caused me to review this info was that the other diagrams that I had been referring to for rivet layout on page 4-20.were based on a single lap joint of two sheets of aluminum,similar to a skin repair. IN my case all of the modes I am performing are to the Leading edge rib, not the wing skin. Sp after reviewing the two diagrams, figure 4-14 told me what I wanted to know. I decided to use the spacing on picture D, which is a doubler plate applied to the rib web over a lightening hole. Basically all this does is change the spacing of the rivets between rivet from 4D to 3D. The 2D edge distance remains. SO I measured the rivet layout based on 2D edge distance and 3D between rivets, and that basically meant that instead of requiring 1 inch of metal, I really only needed about 7/8s of an inch. As it turns out, I kept the 1 inch dimension for reasons I will explain later. Here is the pic of the part with the rivet layout marked:
The line toward the top of the pic was drawn by position the part against the rib web, and using the very bottom of the cutout section of the rib to draw the line. This is very bottom of the rib web that must be reference for edge distance requirements for the rivets near this section of the part.
The two parallel lines that are very close to each other was an adjustment I made toward the flange side of the part. I decided to back off about 1/16th of an inch from the bottom of the attaching flange after recalling something that I read that 2D edge distance is good, but 2.5 D is better. SO I raised the level of that row of rivets by 1/16th of an inch. The edge distance of the part is not affected, but the edge distance of the bottom portion of the rib web will be affected, so I have to make sure I measure this right.
Next came securing the part so I could center punch all the holes (now 6 total instead of 4 as a result of going from 4D to 3D). I also trimmed the top portion of the part based on a line drawn 1 inch from the reference line drawn that represents the very bottom of the rib web cutout for the spar bars. I secured it with bar clamp and center punched all 6 holes:
First I drilled all holes to #40, then deburred and final drilled them up to #30:
These pics turned out blurry so sorry about that. My camera is also flipping them around which I need to figure out how to correct, so sorry about that as well.
I still need to debur the edges after trimming down the top of the part. My scotch brite wheel was buried in the garage due to recent storms and the need to make fast room in the garage for both cars. So I'll finish that later. Here is the part temporarily placed into position on the rib. I will use the holes drilled in the part as a guide to match drill the holes in the rib web. I will need to secure the part into its final position as best I can by securing one flange to the wing spar and the other flange against the back of the rib web.Then I will drill each hole through the rib web and cleco each one as I go.
My rivet layout did not turn out as straight-line as I would have liked it but everything is within specs from 43.13 so tome that is all that matters. Hopefully I will be drilling remaining holes. Then I have to think about some priming before I can drive the rivets - as usual. Sure haven't done any of that in a while. I may prime this rib in 7220 acid etch rattle can instead of my 2 part primer just so I can keep moving forward on this part of the mod.
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