Second Rib Flange Attach holes drilled

Tonight I did the layout, drilled the rivet holes, deburred them, and trimmed the second flange for the 408 rib mod. And here is living proof why you should probably not rely on any measurement details that I provide unless you read way ahead in my posts. I think I provided rivet length dimensions based on 2D of the rivet. This is wrong. The length of the rivet after it is inserted into all parts that being joined is supposed to be 1.5D and not 2D. SO the math for the rivet length is 2 x .032 (thickness of the rib web and the new flange), + 1.5D x the rivet diameter.

SO that is 2 x .032 = .064, + 1.5 x .125,or .064 +.1875 = .2515 total length. A 4-4 rivet is .25 inches long (4/16ths), so a 4-4 rivet is just under the correct size for the rivet required to attach both parts. I did a trial fit and the 4-4 rivet will work just fine. Originally I thought I needed a 4-5 rivet which is way too long.

So, make sure you read ahead because my initial math may be off just a bit. One thing about being off the project for extended periods - you have to relearn a few things that used to be common everyday knowledge. That is why I am so deep into AC 43.13 to make sure I do this right.

This flange is a bit wider than the first one, so my rivet spacing was widened accordingly by about 1/16th of an inch. Here are the pics:

Next step is to final trim, smooth all the edges, and then securely attach both parts to the rib on the spar so I can match drill all the rivet holes to the rib web. Then prime, then rivet them to the rib. I I may drill the final hole through the actual flange that will be riveted to the main wing spar, but I wont set that rivet until all the LE ribs are ready for riveting. Then I need to fabricate 2 more flanges for the other rib on the right wing. These are small gains, but considering this is exactly where I left off last August, this is still progress. Funny that it takes all this extra time to try to make one rib look and function just like another rib. Sure wish I could ahve Vans make a 709 rib with skin flanges bent .032 smaller for the joiner plate, just like the 408 rib. Sure would have saved me a lot of work.