The edge-distance fix by Bob Collins

A few months ago, I wrote an article for the RV Builder's Hotline after I realized I'd violated the 5/8" edge distance when I mated my airplane's wings and drilled the bolt hole after setting the wing incidence. As the article noted, I replaced the entire rear spar doubler, but decided not to replace the "fork" that extends out of the fuselage of my RV-7A. Why? I thought it would be too much trouble and, possibly, lead to further problems when trying to drill the rivets out of the 705C doubler. Specifically, two of the rivets also attach the seat ribs to the 705 bulkhead.

You know what happened next, because I bet it's happened to you. I replayed the replacing of that piece over and over in my mind, usually while trying to get to sleep, or while trying to stay asleep early in the morning. That's usually a good sign that there's something you need to do on your homebuilt airplane project. Your brain won't let you rest.

Since I was a little ahead of my schedule for getting the canopy frame situated (I'm trying to time it so I'll be ready to cut the plexiglas when it's about 90-100 degrees this summer), I decided now was as good a time as any.

If I wanted to -- I don't -- I could consider replacing the 705B doubler too. That's the bar that goes across the entire fuselage, and forms the rear part of the fuselage "fork" on both sides. My misdrilled hole is on the right side. But I'd also drilled the bolt hole for the left wing and that came out perfect. To replace the whole bar would require me to also remove and replace the entire rear spar doubler on the left wing, just as I had with the right wing. It also would require drilling out a lot of rivets inside the fuselage, many in very precarious positions.

I opted not to do it, mostly because the hole I drilled in the rear fork is fine, and -- if I make a decent drill bushing for the task next time -- should be quite usable for the "new" doublers. I should be able to get a straight hole.

I hadn't yet closed up the interior of the fuselage, although since I'm one of those people who put nutplates on both the seat and baggage floors, getting access to the parts was not a problem. Even with the flap mechanism installed, you can gently bend the floor to remove it, or at least tip it up enough for access.

The two brackets for the seat belts need to be removed first; not a difficult task since they're bolted in. Next, remove the bolt that holds the short spacer in place and then use a chip chaser/screwdriver combination to pull it out of the installation. The one flush head rivet in the installation is exposed when the seat belt bracket is removed.

The universal head rivets present no significant challenges, except for the two that also attach the seat ribs. If I'd listened to the old -- and often debated -- axiom, "shop head on the thinner material," I wouldn't have had any problem here. But I didn't. All of my shop heads were on the forward side, the doubler side, rather than on the thinner material of the 705 bulkhead.

Now, there's some advantage in doing this. In removing most of the rivets, the part beneath is going to be sacrificed. So drilling the heads off, or even grinding down the heads, would not be a problem -- except for the two that are in those ribs. Had I put the shop heads on the aft side for at least those two locations, it would have been much easier for me to drill them out.

As it turned out, only one presented a problem, and I enlarged the hole enough in removing it, that I decided to drill the hole out to a #12 when the new part goes in, and use a bolt in that position. I also made a slight nick in the seat rib flange, which forced me to stop-drill the certain crack that would follow at some point.

After drilling out all the rivets -- and, by the way, I experimented using a #40 drill bit in my rivet removal tool, but just couldn't snap the heads off cleanly, so I switched back to a #30 drill bit -- I just used a screwdriver and a rubber mallet to gently tap it loose. It's a tight fit, because it weaves behind those two ribs, but once you can get it to move slightly, you can then grab onto it from the outside with a pair of pliers and pull it the rest of the way out.

Inspecting the old piece, I felt that I had definitely made the correct decision. The rear spar bolt hole was elongated, confirming my original suspicion that the cause of my original mess-up was that I went to the reamer too early in the drilling process.

When I ordered the parts for the rear spar doubler replacement months ago, I also ordered some bar stock, just in case I decided to go ahead with the 705C replacement. I couldn't find on DWG 20, however, what the original size of the piece was to be before the two bends in it (the ones to form the "fork.). The drawing indicated 12 1/2" after bending. So I just cut the piece to 13 1/2", made the bends as indicated (and using the old piece as a guide), and then placed the old piece over the new piece, drew the outline of the tapered edges, cut new piece down to 12 1/2", used the bandsaw (thanks, Dad!) to make the tapered edges, and then filed it down to make it... dare I say... perfect.

There's something to be said for not sacrificing the old part when removing it and using it as a drill guide is one of them. This saves you from having to remount and drill through the existing pieces. Clamping the two pieces together and using the drill press should give you -- at least it gave me -- a piece that should easily align with existing holes.

That done, I simply tapped it back in place, clecoed it to the 705B doubler, and then checked the bolt holes to see if the bolts would fit -- they did. I drilled that rib attach point I mentioned earlier out to a #12 -- then removed the new part for alumiprep, alodine, priming (after countersinking for that flush-head rivet beneath the outboard seat belt attach bracket).

I reinstalled the part, and riveted in place. Estimated time: 6 or 7 hours over a weekend (to give the part time to dry.

Taking the time to make the fix, solves so many problems, not the least of which is me getting a more restful sleep. It also virtually assures a good rear spar attachment for the plane, and it keeps me from having to think of a way to drill the bolt hole in an existing hole, through the new rear spar doubler I installed a few months ago, and then out the existing hole in the forward fork.

It really made no sense not to replace the 705C. Why go through all the trouble of replacing the rear spar doubler, if only to end up with another lousy hole, even if it no longer violated the edge distance? This repair guaranteed a proper edge distance for the new hole.

This is also another benefit, I think, of the pay-as-you-go approach to the project. Since I don't have the money -- yet -- to finish the project, and since I'm on schedule for the canopy task, and since I'm not able to fly now anyway, I can go back and fix things that nag me a little bit.