Fabricating Tank Attach Bracket   October 22nd, 2007

The leading edge of the tank attaches to the fuselage with a 90 degree bracket. This part has to be made from a piece of aluminum angle. The plans have a 1/2-scale drawing and some rough dimensions, but the general idea is that the bracket matches the contour of the front of the rib.

First, I sketched out the outline in the angle. I used a hacksaw to cut it slightly to shape, and then used a belt sander for the final shape.

For the other side of the angle, which is supposed to match the contour of the rib, I used the backing plate (which goes on the other side of the rib, opposite from the bracket) to draw the shape to cut. The bottom of the backing plate overhangs the angle by a little bit.

Again, I used a good old hacksaw to cut the shape slightly larger than final size, and then a belt sander to get it to the final shape.

Finally, here is the bracket fitting nicely on the tip of the tank rib.

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Drilling the Tank Skin..   October 15th, 2007

Nothing too exciting here… I took the tank off the wing and match drilled all the holes…

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Fitting the Tank Skin   October 9th, 2007

I first tried to assemble the ribs and fuel tank skin in a cradle, as called out in the manual. Pretty quickly I figured out it wasn’t gonna happen. The skin goes on so tight, I don’t know how you can make things match up in a cradle.

So, I decided to use the same method I used to fit the leading edge skin. I assembled the baffle on top of the spar, and clecoed the ribs to it. I also clecoed one side of the skin to the rivet holes. To keep the ribs from moving out of place when the skin is ratcheted down, I placed wood dowels between each rib. I made each little dowel to fit each individual rib, and yes, it was a pain in the neck, but in the end it was worth it.

Note that I tried ratcheting down the skin as shown in the two pictures above. I couldn’t quite make the holes match. I then switched sides — clecoed the top side and let the bottom side free — and tried ratcheting down the skin again. This time things matched up pretty well.

Here is the end result…

Finally, I went back to check the leading edge to tank fit, and it couldn’t be any better…

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Matching the Tank and Leading Edge   September 23rd, 2007

In order to make sure the fuel tank and the leading edge match up as perfectly as possible, I assembled the baffle and tank skin on the spar (with no ribs), and moved it up to mate up with the leading edge. When they matched nicely, I drilled the baffle to the first two Z-brackets and put clecoes in.

I then removed the skin and drilled the rest of the baffle/Z-bracket holes.

Not too many pictures of this process; I have been busy helping with stuff around the house, and decided to focus my free time on building and not so much picture taking.

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Drilling Tank Z brackets   September 22nd, 2007

The tank is attached to the wing with a bunch of screws around the edge (both to the spar and to the leading edge). In addition, there are 7 aluminum brackets that hold the tank secure to the spar. These come undrilled, so you have to measure and drill the holes that will hold the bracket-to-spar screws, as well as the bracket-to-tank rivet holes.
The first step is to mark a line down the center of one of the flanges:

Once the first hole is drilled, you use the holes in the spar as guides to drill the other two holes. Rather than place the bracket on top (where it should be) and drill from the bottom, I placed the bracket on the bottom, and drilled it from the top. This way I had better control of the drill, and I could clearly see the centerline. I used a big C-clamp I bought at Harbor Freight for about $1 to hold the bracket in place…

The result is a bracket with the holes nicely matching the spar holes..

And here is the spar with the first z-bracket drilled and clecoed to it… 6 more to go on this wing..

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The Tank Attach Holes (All 360 of them!)   April 9th, 2007

It seems like I’ve been drilling holes for the past three weeks or so!

The first task on the wings is to drill and countersink the holes for the tank attach platenuts. The fuel tanks on this plane are part of the leading edge of each wing. They attach to the wing with a total of 60 screws. Each screw goes into a platenut, and each platenut is attached to the spar with two rivets. So, each spar needs a total of 180 holes. The center hole (where the screw goes through) on each platenut needs to be countersunk so the tank skin can sit flush with the spar flange.

The problem is that as you countersink the spar to allow the skin to sit flush, the hole will start enlarging, and the countersink pilot will start to wobble. Van’s Aircraft recommendation is to first rivet the platenuts to the spar, and then use the platenut itself as a guide for the pilot. I wasn’t convinced this would work out quite right, so I decided to go with another method I saw on Dan Checkoway’s web page.

First, you clamp a piece of aluminum angle under a set of platenut holes. Then drill through the center hole with a #30 bit, being very careful to keep this hole centered concentrically with the larger screw hole. Then, match drill the two rivet holes with a #40 bit. The result is this:

Since some of the holes are parallel to the spar and some others are at 45 degrees, I drilled both patterns in one piece of angle (some other holes are at “-45” degrees, so I used a separate piece of angle for those). — Oh, and don’t pay attention to the countersinking on the middle hole on the right. This happens as you start countersinking and the spar hole gets enlarged.

To start countersinking, I first clecoed the angle to the spar:

Then I used cleco clamps to hold the angle in place, and removed the clecoes (because the countersink cage won’t fit with the clecoes in place)

Finally just place the countersink pilot through the pilot #30 hole and countersink away! No wobbling, no chattering, etc.

I then used a piece of aluminum dimpled for a #8 screw to make sure it would sit flush against the spar flange.

Of course, I then tested with an actual screw, and didn’t like what I saw at all 🙁

The countersink is a lot deeper than it needs to be. Van’s advice is to countersink enough so the screw head sits flush with the spar flange surface, and then go ‘a few more clicks’ deeper. One click in the countersink cage is 1 mil (0.001″), so they probably mean about 5 mils deeper.
Even if the dimpled piece doesn’t sit exactly flush now, it will be flush once the screw is holding it down.
Fortunately, I only screwed up one of these holes. I used Van’s recommended depth for the rest of them, and they all turned out much better.

Today I finally finished countersinking all the tank attach holes, as well as the inspection plate holes. There are three inspection plates on the bottom side of each wing, and each one has four screws going into the spar flange (and a bunch other going into the wing skin).
Here’s one of the spars ready to have all the holes primed:

Oh yeah, did I mention how many freaking holes there are in this thing??

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