Wings 13, Total 476 - Pick Your Poison and Deal With the Results

What I mean by pick your poison and deal with the results is a reference to the method you decide to use to countersink all those pesky fuel tank and Inspection Access Plate mounting holes - use Vans #30 countersink through the nut plate, or use the Angle backing plate clamped to the inside of the spar flange as I have done. Either way, you might have some demons that you have to resolve, and I certainly now have mine. More on that later.

I started the day by repositioning the angle to finish the second half of the first side of the left wing spar. Yes, I still have 3 more sides to finish - the other side of this par, and the remaining 2 sides of the other spar. I learned some things about being efficient during this process, so it has been somewhat educational.

After I finished the fuel tank holes, I had to pause and do some more research regarding the depth of the countersunk holes for the nutplates for the wing inspection access plates. These are a series of 3 inspection plates along the bottom of each wing that allow you to check inside the wing during inspections to to access certain components. Part of these plates attach to the wing spar, and the remaining 3 sides attach to the wing skins that surround them. I had to research them because the size of the nut plates and screws where these attach to the spar are different from the ones for the fuel tanks. The fuel tanks use a number 8 screw, which is bigger than the #6 screw that is used for the inspection plates, so the countersink hole size and depth and the drill bits and countersink bits used to create them are different as well.

What I found was this: Recommended size range for the Fuel tanks is .365 - .375 for the countersink dimension. tools used are a #21 drill bit followed by a #19 drill bit and a # 19 countersink bit.

Size range for the inspections plates is supposed to be less than .1325 inches, and there is an edge distance concern here because the countersink for this hole will take you almost all the way to the edge of the spar flange.  The tools used for this one are a #28 drill bit, followed by a #27 drill bit, nad a #27 countersink bit.

I really had to dig for this info on VAF. I also found the instructions from Vans to be horribly inadequate, as usual when it comes to new construction or steps that require a great deal of detail to ensure they are done correctly. One example is that they do not even reference one of the plan drawings that clearly shows the attach instructions for the nut plates fo the inspection plates. I found it by looking ahead in the plans, and I think it is DWG 17A but will ahve to check again to make sure.

I started by making a test hole for the smaller #6 screws and drilled, deburred, and dimpled one of the 6 inspections plates for the wings.

Here you can see that the first hole I countersunk was way deeper than the .3125 dimension I found on VAF.

Well and the next picture sure sucks - did not realize how blurry it was so may take another one tomorrow. I was trying to show something that NOBODY seems to show after they finish countersinking their holes to the sizes mentioned previously, and I mean NOBODY anywhere. I found it absolutely incredible that nobody shows how the screw heads sit down into the slightly enlarged countersunk holes, which is necessary for the thick tank skins and inspection plate skin dimples to sit down in the countersunk hole correctly. SO here it is, and I will get a better one tomorrow.

The .370 screw head is the #8 screw for the fuel tanks, and the .325 hole is the first test hole I drilled for the inspection platess, I backed off this to get closer to the .132 recommended max size hole for the inpsections plates.

When you do all this drilling, you will get aluminum everywhere. This is just a small part of the mess that is made during all the countersinking activity.

And now for a pic of my one screw up so far. I think I can fix this, and it happened on one of the holes for one of the inspections plates and NOT on the fuel tank attach holes, so that is another good thing. My method of using the backing plate and a very long piece of aluminum angle leaves a ton of clecoes on the work piece. You have to be sure you know which hole is whichm and this is difficult because when you start drill holes to final size and then use the microstop countersink tool, you have to move clecoes back and forth quite a bit. Well, I got caught in my own cleco madness when I went to drill one of the holes. I accidentally placed a #28 drill bit through one of the #40 holes for the rivets that attach the nut plate to the spar, and, you guessed it, I drilled a very large hole in a place that was supposed to have a much smaller one.

I can easily fix this with an NAS 1097 "Oops" rivet that has a 1/8 inch shank, but I need to figure out how to enlarge the hole in the nut plate. I just about took my finger off trying to drill out the #40 hole to a #30 in the AN507 6R6 nut plate. The drill bit snagged the hole in the nut plate and ripped it out of my fingers, mangling the nut plate in the process and turning it into a very fast moving projectile across the garage. Bad news all around. So if I can figure out how to get a nut plate for a #6 screw with a #30 rivet hole on one side I am OK. Otherwise it's a call to Vans to figure out what to do. The pic show the hole that I circled that is obviously larger than it is supposed to be. Lesson learned - be very careful about which hole you are drilling - it is very easy to get confused, especially if you get distracted.

You can also see just how close the inpection plate countersunk holes cone to the edge of the spar. this is the way it is supposed to be. Just make sure you hold the countersink absolutely flat against the spar flange or you may go right through the edge. You must alos use a step up process when setting your countersink depth. The tool allows you to set the depth very precisely, but I ahve found that with the 3 fluted bit that I using, sometimes a very dsmall adjustment can result in a rather large amount of material being removed, whereas one or two previousl small adjustments result in almost no change at all. So this is a rather tedious process but it is one  that is critically important to get correct. Spend the time with the test pieces and measure with a digital caliper. That seems to work rather well to set the correct depth.

And lastly is a pic that shows the aluminum angle in its new position one the second half of the holes that required countersinking. I first thought that I would be able to use the same side of the angle that I drilled the first set of holes to finish the second half, but I soon found out that the hole patterns are slightly different as they move further outward toward the tip of the spar, so I had to switch sides to the undrilled side, reclamp the angle to the spar, and drill new holes in everything. I started with the #40 rivet holes on either side of the center hole for each nut plate. Once those were done I final drilled the center holes for the tanks (2 passes with each drill bit mentioned at the beginning of this post), countersunk those holes, and then final drilled and countersunk the holes for the inspection plate nut plates.

The truth is that even though the countersunk holes for the inspection plates are almost to the edge of the spar, they still come up way short of allowing the #6 dimple to set nicely in the countersunk hole so that the skin of the inspection plate is flat against the spar flange. Will probably have to discuss that with Vans as well.

I need to countersink the #40 rivet attach holes as a final step, but as part of the efficiency of this process, I will probably wait until all the other holes are drilled and countersunk on this spar and also on the right wing spar, so that I don't have to reset the countersink tool over and over again. I started using my second air drill that I purchased from the auction, which came in very handy for final drilling with the two different sizes of drill bits I needed for each hole. It was still a bit of a pain because I have a special short Air fitting on my Sioux air drill that accepts a special light weight hoes assemby that I purchased with my tool kit long ago, but the air drill I purchased from the auction has a standard fitting atached to it, so I have to disassemble a section of my air hose each time I switch drills. I will remedy this by purchasing another set of connectors that will fit the light weight hose and will replace the standard fitting on the drill with one of those. Then I can switch drills fairly easily. It would be even better if I had a manifold assembly with a different hose so I could keep both of them attached all the time. Working on that one as well.

So next steps are to focus on drilling and countersinking all of the fuel tank holes on both wing spars, followed by the inspection plate holes, followed by the #40 rivet holes. Then I get to do a lot of deburring, priming the countersunk holes, and finally riveting all the nut plates in place. Several more long sessions coming up to finish this.