April 16, 2009

Preparing to Drill Holes for Gear Leg Mounts - 2.0 hrs.

I wrapped up one more little item tonight before moving forward. I finished carefully enlarging and smoothing out the hole at the very aft end of the fuselage for the tie-down ring. It's been laying on my workbench as a reminder for a while now, and it felt good to finish that and put it away. I didn't get a picture, though. Sorry.

Anyway, the next step called for is to drill open some holes in the bottom forward skin F-772 for the gear leg brackets to poke through. I didn't think I would be messing with gear leg brackets this soon. Amazing! So I pulled them out from inventory and studied the plans.

Drawing 34A has a full scale template showing where to drill the holes for the gear leg mount and the brake line. I figured I could just lay the corner of this drawing down on my photocopy machine and make a copy to work with. Then, carefully cutting out the shaded area for the hole, I now had a full-scale working template to use on the skin.

I clecoed it in place on the skin and used my sharpie to mark the hole. The holes in the template lined up very accurately to the holes in the skin, so I think I'm pretty safe in assuming that the scale of the template is accurate enough.

After removing the template, I'm ready to cut and enlarge this hole, and also enlarge the pilot hole for the brake line. I think I'll make the big hole a bit undersized at first, and sneak up on the full size carefully. We'll see how it goes. The hole actually cuts into the F-704 bulkhead flange a bit, as well as the underlying center section bottom skin (can't see it here, it's underneath). It comes dangerously close to one rivet.

Then I flipped the template over and repeated all of this on the other side.

Next, the bottom skin is removed to cut the holes. While it's off, this is a great opportunity to see how the gear leg mounts fit in the corners. There's a thick stiffener skin doubler that goes in here, too.

Sure enough, the gear leg tube on the mount bumps into the edge of the F-704 flange and skin on the upper right in this picture. So my first task will be to trim away the small curved cookie-cut so this mount can nestle in to the corner where it belongs. My strategy is to fit this bracket in place, then enlarge the hole in the bottom skin until it fits just right over the bracket.

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