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Kurt Haller RV-9A
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Date: 11-28-2015
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Number of Hours: 0.00
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Manual Reference:
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Brief Description: Light-guided match drilling: cowl to half-hinges
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This entry written 29 Aug 2016. Hours not tracked.
The half-hinges that attach to the cowl edges were pre-drilled on the bench first. #40 holes for rivets at 1" spacing, Later, #10 holes halfway between rivet holes were made to give mechanical grip on the hinge from a layer of epoxy/flox binding the half-hinge to the cowling fiberglass. The rivets, to be installed while the epoxy is wet, will be slightly under-squeezed so as not to stress the fiberglass. They will essentially provide clamping force until the epoxy cures and takes the majority of the load.
With pre-drilled half-hinges mated to their partners on the firewall flange, the top and bottom cowling could be put in place with duct tape aligning everything and a few holes were matched drilled the normal way to get started. But it was much easier to set a bright light on the inside to locate holes from the outside. Hitting the open hole in the Al beneath the fiberglass with minimal enlargement wasn't hard. A bad miss resulted in an elongated hole in the fiberglass. (It's softer than the Al, so the drill was pulled sideways as it entered the Al hole). Since the epoxy flox bond will bear most of the load, a few imperfect rivet holes in the fiberglass don't matter.
The imagess show how the side hinges where drilled to the top cowl. The bottom cowl side hinge holes were easy to match drill the usual way, from the pre-drilled Al side, on the bench. Then the top half of the side hinges were zippered on, and a light from the inside the assembled top and bottom cowling guided drilling the #40 holes holes in the top cowl.
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Seven rearmost holes left to drill
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Close-up of those 7 holes.
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Pilot side completed!
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