Matt's RV-7 Project

The plans tell you to "slip the W-412 tip rib into place", but with the wingtip clecoed to the wing there's no obvious way to manipulate the rib once it's inside. I solved this with a couple strips of duct tape:

Once I was happy with the position of the rib, I marked and drilled the rivet holes in the top and bottom:

The flanges on the tip ribs interfere with the nutplate reinforcing strips I glued to the inside of the wingtip flanges, which I suspected would happen. I guess I could have planned that better, but it's no matter, as I actually came up with an improvement while dealing with this. First I relieved the rib flanges to fix the interference:

I replaced the cut-off rib flanges with some pieces of aluminum angle that sit on top of the wingtip flanges and their reinforcing strips. This will end up being stronger than the stock design, since forces acting on the tip rib will be transferred to the wing structure via the three aftmost screw holes:

Finished ribs after riveting the modified flanges:

I countersunk the rivet holes and then attached the ribs to the wingtips. To avoid cracking the thin fiberglass, I erred on the side of slightly under-squeezing these rivets. Here you can also see how the add-on rib flanges sit on top of the reinforcing strips:

One of many test-fitting sessions to make sure everything is lined up:

I'm happy enough with the way the wingtip ribs turned out. I could have done a better job of planning ahead, but I'd probably use the same basic approach again. I think this is going to be stronger than having a rib that's supported by nothing but flimsy fiberglass.

Continuing with wingtip fitting, I block-sanded the trailing edges until they were even with the ailerons:

This caused the trailing edges of the wingtips to become awfully thin, and I was worried about them cracking or splitting. I decided to reinforce the trailing edges by pouring in a thin epoxy/flox mixture and standing the wingtips upright while it cured. Here you're looking down at the inside of one wingtip's trailing edge, with a flox bead drying at the bottom – a terrible photo, I admit:

This is how I secured the wingtips while the epoxy was curing. The inboard ends of the trailing edges are dammed with clear tape, and the bottoms are leveled, all in an effort to get an even application without making a mess:

Here's the finished result after more sanding. This turned out pretty well, and seems to have added plenty of extra strength to the questionable-looking trailing edges:

Next I trimmed the inboard edges to achieve a uniform 1/4" gap between wingtips and ailerons, and cut back the remaining flanges as required for clearance:

The fiberglass wingtips are large and flimsy, so I've tried to be diligent about storing them in this orientation for all these years. I'd hoped that would keep them from collapsing or becoming distorted – it seems to have worked out, as they're not obviously warped:

The molded fiberglass flanges are slightly oversize and the edge is uneven, so you have to do some trimming. I measured the depth of the skin overhang on the wings (about 5/8", or 20/32") and then made a little marking gauge so I could draw a line 19/32" from the joggle with a sharpie:

This worked out pretty well, and I found I didn't even need to remove very much flange material:

A sweaty session with the Perma-Grit sanding block was enough to trim and straighten the edges, and then it was a process of iteratively trimming off bits of fiberglass until I could get the wingtips to sit correctly on the wings:

Once I was able to hold the wingtip up to the wing, I marked the approximate location of the fastener holes on the outside of the fiberglass:

I couldn't find the W-728 reinforcement strips that come with the kit – misplaced in a move, probably – but since I happened to have a four-foot section of 0.020" handy I was able to just cut my own using tin snips. They ended up somewhat curlicued, but that doesn't matter.

After scuffing and cleaning the mating surfaces, I glued the reinforcement strips to the inside of the wingtip flanges using five-minute epoxy. I used every pony clamp I own to secure each strip as I glued it:

So far I've been following the plans and a helpful how-to article, but here I decided to innovate a bit. I wanted to find a way to pull the fiberglass up to be flush with the wing skin, to make it easier to drill holes accurately and get a good fit. One way to do this is to insert a temporary foam rib inside the tip, or even fill it with party balloons, but it occurred to me that these 3M Command clips might be a viable alternative. We have these things all over our house, and my reasoning was that if they don't pull the paint off my drywall they probably won't pull the gelcoat off my fiberglass either. So after doing some testing on a cut-off piece with favorable results, I proceeded to stick a clip next to every second fastener hole:

With the wingtip held in place, I used some clamps and a folded piece of scrap aluminum to lock the trailing edges of the wingtip and aileron together:

Then after double-checking the alignment of everything, I drilled and clecoed the first hole, starting at the leading edge:

Now here's where the stick-on tabs come into play. Working from front to back, and alternating from top to bottom, I drilled and clecoed every fourth hole, using the adjacent tab to pull the fiberglass flush with the wing skin. A looped zip tie made this easy – I wouldn't suggest using pliers here, as you only want to apply about a pound of force while you carefully drill through:

After drilling all the holes that were next to a pull-tab, I was happy to see that the fit was turning out really nice:

From there it was a simple matter to drill and cleco the remaining holes, and then remove the sticky tabs. Almost all of them came off easily – a few stubborn ones I carefully dislodged with a plastic scraper – and the gelcoat was completely undamaged:

I repeated the process for the other wingtip, with similar great results. I'm very happy with this initial fit:

I still need to trim the trailing edges flush with the ailerons, and clean up the gaps between wingtip and control surface, but the all-important alignment is good on both wings:

Up front, I will have a little cosmetic work to make the profiles of the leading edges match up:

And of course there is a bunch of other work ahead before the wingtips are truly finished, but for now here's a beauty shot showing the plane with its full wingspan achieved at last:

And since it's suddenly three feet wider than it was last week, I'm going to have to be careful not to walk into it: