Vans’ response on my flap skin problem wasn’t exactly what I was hoping for. They’re aware of this issue, but don’t ship replacement skins any more. They suggested using replacement inboard and outboard ribs with no prepunched holes; according to Joe Blank at Van’s, match-drilling those ribs to the skins will fix this problem. I agreed to try their solution, since the replacement ribs are free. We’ll see if they work.

Meanwhile, I did some cleanup work on the flap braces on both wings. One thing I had neglected to do in the past was match-drill them to the lower wing skins. Before I could do that, I had to tweak the braces a bit with a hand seamer to make them line up smoothly with the skins. The braces are left with a bit of a twist due to the way they’re riveted to the rear spar and doublers. With a little adjustment, the braces and skins line up nicely for match-drilling.

With all those shims in place, it was time to drill the flap hinge and lower skins to the skeleton. With the spars and shims drilled, match-drilling the lower skins was easy. Drilling the flap hinge took a little more work, since it’s one, long floppy piece of AN piano hinge. There’s also very little room for error when drilling it with the proper edge distance as specified by the plans.

The first step was marking a centerline on one leaf of the hinge. I fabbed up a homemade edge marker block similar to the one sold by Avery Tools and marked the leaves of both flap hinges. I then clamped the hinge in place on each flap spar, making sure to align the centerline and spar holes. One minor trick…I used small pieces of thin plywood between the clamps and hinge leaf to avoid squeezing and deforming any hinge eyes. A few minutes with the Sioux and a #41 drill bit, and the hinges were match-drilled to the spar. I then match-drilled the entire structure to #40.
Things were going great, I was on a roll…so I decided to finish up by match-drilling the upper flap skins to the lower skins, spars and flaps I had done over the last two days. I grabbed those flap skins, clecoed them in place…and then found a problem. Remember that picture from October 6?
If you noticed before that the trailing edge bend didn’t look right, you’re very observant. Other builders have had the same problem with flap skins delivered in late 2005 and received replacement skins at no charge. I called Vans and reported the problem, we’ll see what they propose.

Another area where shims are required is between the aft end of each interior flap rib and the lower skin’s J-channel. This is one I really can’t understand…why doesn’t Van’s just make the ribs long enough? Ok, enough grousing already.

One minor catch here…the aft-most hole in each rib’s lower flange isn’t drilled. That gets done by using the corresponding lower flap skin as a drill guide. Without a cleco to hold them together, the rib flange and skin must be clamped together tightly before the rib’s rear tab and shim are match-drilled to the J-channel, pulling the tab into the proper position. Clear as mud, right? Anyway, I used a small piece of plywood and a clamp to pull the flange in place, and another clamp to hold the shim in place as it and the tab are match-drilled to the J-channel. The shim gets trimmed to length after drilling.

For some reason known only to Vans, there are a few places in the flaps where shims are required to fill gaps between the skins and adjacent substructure. One place I can understand – a gap formed by the overlap of the upper skin on the lower skin at the outboard and inboard ribs. The upper skin actually wraps around the trailing edge and is riveted to the J-channel formed in the lower skin. Here’s a picture of an outboard rib…look closely and you’ll see an 0.025″ shim under the lower aft side of the rib.
You’ll also see that the skin doesn’t fit well. That’s a topic for a future post.

Got both flap spars clecoed to their respective lower skins and ribs. That was pretty satisfying after all the irritation I’ve experienced with the ailerons. The clamp in the second picture is just to hold the rib in place as one cleco is removed for drilling.