Luis & Fab's RV-7A Construction Log

Another picture of leading edge riveting….pretty easy stuff here…

Well, it’s time to start putting the wings together for the last time!

The first step is to take the previously-assembled leading edges and rivet them to the wing spar. The problem is that The holes for the leading edge ribs are so close to the main ribs, it’s hard to get a rivet set in there (or even the clecos!!) at a 90 degree angle.

After doing a lot of reading, and finding out the factory ‘allows’ the use of blind rivets, I decided to go ahead and use cherry commercial rivets for the leading edge. Because it is so hard to get even a rivet puller in there, I put the rivets in from the top (inside of the leading edge) and contorted my hands and rivet puller inside the leading edge.

Some gung ho people call this ‘cheating’, but I can’t help it but think I’d rather have a nicely pulled blind rivet than a half-assed solid rivet with dents (as well as the possibility of damaging the spar as well)

Here is a picture of what it would look like trying to drive a solid rivet. Notice the holes are so close, not even the clecoes are in there straight. Some people recommend grinding down to offset rivet set to get closer to perpendicular, but from the looks of this, I would actually have to grind down about 1/4 to 3/8’s off the gun itself to be able to get the set close to perpendicular to the spar. No thank you….

Van’s recommends LP4-3 and LP4-4 rivets, which you can’t find anywhere except at Van’s. I instead used Cherry Commercial rivets from Aircraft Spruce. I used BSP4-3 and BSP4-4, which are slightly stronger..according to the data table anyway…

After the leading edge was finished, I found it hard to get the skin to perfectly line up with the holes in the main and rear spar. Even though I have a jack made up of two blocks of wood and a screw-rod, it was still hard to get everything to match. So, with Fabiola’s help I took the wing off the jig and laid it on the table. Every hole now matched perfectly, and I think it was easier to squeeze the leading edge to spar flange rivets.

I asked around and got lots of advice on how I may want to fix this. I posted a picture of the dent and asked for help at Van’s Airforce, and within less than a day I had several suggestions of what to do. I ended up following the advice given by Mark Hegy (I guess the “A&P Gulfstream Aerospace.” in his signature swayed me just a little :-). He basically said to use ‘soft rivets’ and then use a blue and blue scotch-brite discs to polish the rivet/skin.

First I ordered some AN426A-4-3 rivets from Aircraft Spruce. Actually, I ordered about 397 more rivets than I needed (They won’t sell me less than 1/8 of a pound!). Even so, this was my first time putting in a $2 order, and was pleasantly surprised they sent it to me via USPS and charged me only something like $2.50 for shipping, which is very close to what the stamp on the box said.

With the rivets on hand, I took a piece of scrap aluminum, set it between two blocks of wood, and dropped my bucking bar on it (hey — I had to do a practice run first, right?!).

I went through all the steps on the scrap piece, and since I liked the results, decided to try it on the wing. So, this is what I started with — a right leading edge with a small but nasty ding/crack near the tip…

This is the ding after getting sanded down. It is mostly flat, with just the crack and some very thin aluminum in the area.

And here is the final result. From a distance, it will be very hard to tell there is a rivet in there.

Today I fitted and clecoed the right leading edge. I even managed to rivet the entire bottom side. Same process as with the left leading edge, so no pictures!

I discovered that by using a bit of masking tape on the rivets, not only do they stay in place as you rivet, but it also keeps the skin from getting marks or scratches from the rivet gun. Before, I would put masking tape on the rivet set, but it starts desintegrating after a couple of rivets, and it is very hard to take off. By putting the tape on the rivet, the rivet set stays clean and it comes off very easy later.

It took me a couple of days to get all the rivets. Here is the finished product:

Before fitting the leading edge again for final assembly, I countersunk all the holes where the leading edge attaches to the spar. The construction manual doesn’t really talk about this, but the leading edge skin holes have already been dimpled, so in order for things to fit tightly, these holes need to be countersunk (the spar is too thick to be dimpled!!!)

The task is very straightforward — just set the correct countersink depth and start drilling. The only thing to be aware of is that the countersink depth will change slightly depending on how hard you push, and may even drift just a tiny bit over time. I used a rivet to check for the correct depth every four rivets or so.

There are 65 holes on each side of each spar, so that’s total of 260 holes, just for the leading edge. There are a few hundred more where the main skin attaches 🙂

I have put both fuel tanks away, and I am ready to go back to the leading edges. I spend all day today priming the ribs and skins. I am still using the Stewart Systems water-based primer.

The wing jig was briefly converted into a rib-holder. I draped tarps on both wing skeletons to keep paint from getting on them.

After speaking to an AFS rep at Oshkosh last summer, I am going to wait for about a week until I start putting the leading edges together. Given the relatively cold weather, this should be plenty of time for the primer to harden.

Normally, you would use a similar C-frame, but instead of using a handle, there is a shaft you whack with a hammer…painful and easy to put a hole where you don’t mean to. This thing is very easy to use. Just put the skin on it and pull down on the handle. I did both leading edges and both tank skins in two short sessions.

The leading edge rib on the edge closes to the gas tank also has a strip of aluminum where the gas tank screws into the leading edge. This rib doesn’t come pre-punched, so I had to mark where the rivet holes would go before fluting it. I just put it next to the leading edge and marked the approximate location of the holes.

The next step is to insert the rib and the strip into the leading edge. Sounds easy, but the skin is so tight it’s a real bieatch to get everything in there lined up and straight! Even so, I managed to get it in there after a lot of trying…

Finally, once everything was straight, I drilled through the skin and into the rib/strip.

Now I just have to do the other wing…

I got my trusty Redneck ratchet straps and put them around the leading edge. I used some cardboard to keep the straps from scratching the skins.

By the time the holes line up, those straps were TIGHT!