Carrying on from my previous post – there’s one task that RV builders know has to be done right the first time, and that’s drilling the holes in the aft wing spar that set wing sweep and incidence. I’ve already covered all the measurements that verify the wings are in the right position and there’s good edge distance…now it’s time to drill.

Van’s has a good description of the process on their Construction FAQ page, so I won’t repeat their words here. I found a piece of scrap aluminum bar at a local metal dealer and cut pieces to make drill blocks for #30, 3/16″ and 9/32″ drill bits and one for a 0.311″ reamer – to enlarge the hole in stages. The 9/32″ drill seems like an odd choice, but the ideal use of a reamer is on a hole that’s about 1/32″ undersize – and 9/32″ is just that for the 0.311″ reamer.

The pucker factor was pretty damn high when drilling the #30 pilot holes, but they came out fine –

I then worked up to 3/16″, 9/32″ and 0.311″ and ended up with good holes in each rear spar.

Enlarging to 3/16″ wasn’t too tough, but I was concerned about making sure the 9/32″ drill block was centered – don’t want to eat into the edge distance margin. But then I had a brainwave – insert a long 3/16″ pin punch through the 9/32″ drill block and on into the 3/16″ pilot hole, and continue until the punch’s shank hits the side of the drill block hole, centering it on the 3/16″ hole.  Clamp the drill block in place, and voila – the block is centered and ready to use.   Here’s the right side –

Here’s the right rear spar, without an AN5 bolt in place…

The drill block process worked really well – finishing the holes with a 0.311″ meant a nice, snug fit for an AN5 bolt – they went in with only a little finger pressure.  These bolts are supposed to be be a nominal 5/16″ diameter, but they often run undersize. Had I used a 5/16″ reamer, the bolt fit would have been ok, but probably sloppier than I’d want in this application.

So…the rear spars are drilled and it’s a huge relief. I have a backlog of things that need to be done to the wings, like rigging the ailerons and flaps, and it’s time to make some serious forward progress.