Now I need to countersink the holes along the front of the F-776/F-704 spar as per the Drawings and Vans Construction FAQ. Of course I really took my time with this. A person really doesn’t want to screw this up so I really wanted to be sure which holes needed countersunk.
As I am building a RV-7A I need to countersink the first five holes on each side, then after that only the 11, 19, 27, 35 review holes get countersunk. My plan is to go with Vans Option #1 and to dimple all the other holes.
One of my big questions is what to countersink the rivets to. According to the AutoCAD drawings that I’ve done on countersink depth. A countersink diameter of 0.208” is ideal for accepting a dimple in 0.040” thick material. However I’m extremely reluctant to go that depth...also I have to counter sink the topside of the main spar on the outermost 5 rivets. Makes me a bit nervous. I settled on slightly under countersinking with a diameter of 0.194”. I don’t think it will be too big a deal is not...Better safe than sorry right???
Once I was done that, I got some help flipping the centre section back around and began disassembling.
I had a good look at all the front webs of the F-716 seat ribs to determine the edge distances on the AN3 bolt holes. Most of the holes look good however a few are boarder-line with good edge distance so I plan on building doublers for most of the flanges as per Van's tech support suggestion (See the July 7-19 blog). This will make for a solid and uniform installation. Here's a good look at all the ribs.
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