Saturday, May 19, 2007

Preparing the Main Spar

To begin construction, rivet the fuel tank attach plate nuts to the spar. To do this you will have to machine countersink the spar flange for #8 screw holes and AN 426 3-4 rivets. The problem is that the instructions call for using a #30 countersink w/ microstop for the #8 screw holes. As you will find out the holes are already bigger than the #30 so the pilot for the cs will want to crawl around. The fix, configure a template out of scrap angle alum to help the #30 pilot. Here you can see the template I have made for the plate nut countersinks. The middle holes are #30. It will be clamped under the spar flange. I also made a dimple sample for #6 and #8 screws out of scrap .032 alum. I will use it to help judge the depth of the countersinks and ensure the fit. You will also have to predrill all of the #40 holes for the rivets before starting the CS process.

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