The fuel tanks attach to the main spar, but they also attach to the fuselage at the leading edge with a big bracket made from 3/16" aluminum angle. Did I mention that these things are beefy? Well they are. The first thing to do is to cut the angle to length which in this case is 3-3/4".
There are also doubler plates that fit inside the inboard and outboard ribs of the fuel tanks. In the case of the inboard rib, the doubler plate is opposite of the attachment bracket and must be match drilled with it and inboard rib. The doubler plates shown below are precut by Van's to the leading edge shape, so they only need to smoothed down with a file and then a little bit on the Scotch-Brite wheel to finish.
With the attachment angle cut to length it was time to trace the leading edge shape onto one side and then follow the dimensions from the plans on the other. The plans leave out some of the necessary dimensional information, but it doesn't seem to be too critical so I'll just keep going. The missing dimensions are the radius at the top of the flange which is labeled R1 on the plan, the width of the base of the flange, and the lower radius where the flange meets the base. I think Van intended that we just freehand a pleasing shape here.
Shown above are the right and left attachment flanges as cut (on right) and after smoothing and polishing (on left). And below is the finished product after laying out and drilling the attachment holes. In the left tank I'm using a flop tube fuel pickup for aerobatic operation. With a flop tube, the fuel exits the tank near the leading edge, hence the big hole in the left bracket.
The fuel tank access hole is cut from the inboard rib. The center of the access hole is found using a geometric construction from your high school geometry class. Oh, your dog ate that home work? Ok, draw a vertical line through the circle to be removed about midway between where you think the vertex might be and the left or right edge of the circle. Now bisect that line and extend it across the circle. The bisected line will pass through the vertex. Repeat this process starting with a horizontal line through the circle and you will have found the center of the access plate where the bisect lines cross.
Because I'm a just a crazy daredevil with life insurance, I've elected to apply a fly cutter to this task. I adjusted the drill press to its slowest speed, 250 RPM, so as not to miss any of the carnage. I crossed my fingers and let it rip. Fortunately, no one was injured during this process, but it is a bit scary. It may be too intense for small children.
And finally, the access hole doublers. The nutplates are attached to the inside of the doubler and flush riveted to the rib. The access plate will then be able to seal against the rib's smooth outside surface. The doubler is used as a drill guide to drill through the rib for the attachment screw holes.
Carol came down to help out with match drilling the leading edge doubler plates and attachment flanges.
And a little deburring...
Then match drilling the flanges of the fuel tank fillers and drains.
And finally, dimpling the skins and stiffener plates. The tank is now ready for assembly!
No comments:
Post a Comment