VS Spar Holes

[DanH]

A quick heads-up on a detail common to many RV models, the 6, 7, 8, and 9 for sure. I've not worked with the others.

I'm seeing mount holes drilled in vertical stabilizer spar doublers without regard for proper edge distance. I'm speaking of the holes for the two AN3 bolts clamping the VS spar to the elevator up-stop angle.

None of the plans I've seen specify a dimension for the distance from the edge of the VS spar doubler to the hole center. I spoke with Ken at Van's this afternoon. He said the plans don't show a dimension because the hole location is determined by standard practice, ie, 2 bolt diameters minimum from the doubler edge to the hole center, 3/8" in this case....which is perfectly sensible. He and I both think builders are looking at the rivet row (the rivets attaching the doubler to the VS spar channel) and placing the 0.1875" holes in that line. Things get worse when you throw in some sloppy marking, centerpunching, and drilling.

Ken isn't aware of any failures in the fleet, and surely there are airplanes flying with misplaced mount holes. However, the most highly loaded material in a VS spar doubler is at the edge. A hole is something like a 3x stress multiplier, so a hole too near the edge isn't a good thing. Edge distance at 2x diameter is a minimum; an extra 1/8" inboard would be better.

[jferraro17]

Thanks for passing this on Dan.

Joe