Tail Kit

I riveted the bottom rib together tonight. The rib is formed in two parts, one on each skin, and then riveted together. I started by riveting the aft-most 8 rivets on the right skin, For the aft-most two rivets, there is barely any clearance. Some builders use very thin bucking bars, but it’s easy to make a mess. Given my skill-level, I took the safe option and pop riveted the last two holes. These are counter-sunk pop rivets, and when the airplane gets painted, they will look just like the rest of the rivets.

Then I pop riveted the two parts of the rib together with 11 pop rivets:

These turned out to be a real pain, especially towards the aft end. I fabricated a “wedge tool” to act as a shim, allowing the rivet puller to angle away from the rivet, but still have the rivet head be flush with the surface. Several of the rivet shafts snapped off part way down the shaft, instead of flush with the rivet head. I trimmed them with side cutters, but it is frustrating to have it happen. I don’t know what I’m doing to cause the issue, I’ll have to do some research.

Then I clecoed the rudder horn brace, but didn’t have time to start riveting this tonight. It was a very tight squeeze, but I eventually coaxed it into position.

This afternoon I stopped by a fellow Chapter 338 member’s shop to check out his RV-9 build, and to borrow a 6 foot long bucking bar. It was a super helpful visit, and I picked up some good tips. The bucking bar is to back rivet the rudder trailing edge, once I finally get to that step, hopefully this weekend.

I switched to my other hand pop rivet gun, and it produced better results. I installed the spar and top and bottom ribs, pop riveting the spar to the shear clips. Everything went well, and the results look good.

The next step is to rivet the bottom rib to the right skin and attach strip. Looking at the last two holes, it will be very challenging to get rivets in there. I think I’ll follow the advise of some other builders (and Vans), and pop rivet the back two holes. Once the aircraft is eventually painted, it won’t be noticeable.

With some help from Jen and Joyce, I was able to rivet together the left and right rudder skins tonight. The stiffeners on each skin are tied together with a single pop rivet, and the forward ends are pop riveted to the shear clips. There isn’t a great deal of clearance, so an assistant is needed to hold the skins apart while setting the rivets, from bottom to top. I had an annoying issue with the pop rivet tool where the mandrel was breaking off half way instead of flush with the rivet head, after fully forming the rivet. I had to trim off the mandrel on about half the rivets, which was a real pain. With the lack of clearance, I couldn’t get very flush with the rivet head, but it’s good enough given this will be completely enclosed. I’m going to need to figure out the issue, but it worked ok for tonight.

For the trailing edge, I picked up a tip from my EAA chapter and bought a couple of shelving channels for $5 from Home Depot. They are straight, narrow, and have holes cut that are an almost perfect match for 3/32 clecoes.

I taped the trailing edge, and clecoed one channel to each side of the trailing edge, giving a perfectly straight edge while the glue sets. Hopefully this will help the edge to stay straight while riveting.

After a little practice on some scrap aluminum, I back riveted the stiffeners onto the right rudder skin tonight. It was getting late by the time I finished, so I didn’t try to tackle the left skin. Riveting at midnight isn’t ideal with young kids sleeping in the house. It was a little slow at first as I measured each rivet with digital calipers to calibrate my technique. In the end I was moving quickly and getting a consistent head on each rivet. A couple of rivets ended up driven slightly more than I was aiming for, but are still within tolerance.

This was my setup, with a practice piece on the back riveting plate.

I started with this stiffener, and was happy with the results. I later increased the PSI from 20 to around 22, and the difference was noticeable; fewer hits needed to form the shop head. I’m using a 3x gun, which has a lot of power.

Here are all the stiffeners fastened to the skin:

I realized yesterday that I don’t have a #40 countersink that will work on the trailing edge wedge. Because the countersink is flush with the side of the wedge, but the hole isn’t (it’s perpendicular to the chord of the wedge), I need a countersink with a short and/or tapered pilot. I could probably grind one down, but I only have one. So I went ahead and ordered the special part from Cleveland tools. $20, and will arrive on Monday. That means I can’t finish the rudder until next week, but what’s the rush? I can always start on the Horizontal Stabilizer.

I finished dimpling all of the rudder frame components tonight. It was a straightforward process, except for a couple of spots on the spar where the shop head interfered with the squeezer. If I had oriented the rivets so that the manufactured head was on the forward side, it wouldn’t have been an issue. At the time I set these rivets, I was thinking about putting the manufactured head on the side with the thickest material, but in hindsight I would have set these the other way around, since the shop head is a fraction of on inch too high to get the dimple dies to sit square to the hole. Not a big deal, I was able to use a hand tool to get a reasonable dimple on them.

Tonight I finished deburring the other rudder skin, and then took apart the rudder frame which was clecoed together. I made a mistake at one point, as I was deburring a hole in the skin with a counter sink in a hand tool, the tool slipped out of my hand and fell sideways while the countersink pilot was in the hole. This levered up and bent the skin, so I ended up with a bend up on one side of the hole and a bend down on the other. Luckily the skin didn’t crack, but it was very frustrating. Then I started the dimpling process by dimpling both of the skins. It was a long process, as I went slow and tried to avoid any scratches or mistakes. I started with the hole where I had bent the skin while deburring. As I hoped, putting a dimple in the hole straightened out all the damage, leaving no trace of an issue.

Next steps on the rudder will be:

– dimpling the stiffeners, ribs and spar – Monday

– counter sinking the trailing edge wedge – Tuesday

– back-riveting the stiffeners to the skins – Wednesday

– riveting the shear clips to the spar – Thursday

– pop riveting the skin stiffeners (with skins attached) to the shear clips – for this step I will need help; maybe Friday night

– riveting top and bottom ribs – Friday

– riveting the trailing edge – Saturday

– rolling the leading edges and pop riveting them together – Sunday

If all has gone well, it will be finished!

Tonight I clecoed together the rudder in preparation for final drilling the trailing edge and ribs (counterweight support and tip rib). It’s interesting how some parts are punched to final size, while others are not and require final drilling. At least all the stiffeners and corresponding skin holes are final size, that will save me drilling and debuting several hundred holes.

First I clecoed the ribs and stiffeners to the spar:

Then measured and cut the trailing edge wedge to length, and marked the skin where I’ll scuff with scotchbrite for extra adherence of the tape that will hold the wedge and the skin together while it’s riveted.

Then it was time to cleco the skins onto the frame. Here’s a picture of the whole structure clecoed together:

The next step will be to final drill the trailing edge holes in the skins and the trailing edge wedge. You can see the end of the wedge in the picture:

Drilling the trailing edge is tricky because the hole must be perpendicular to the chord line of the wedge, which means it intersects the skin at around 84 degrees instead of 90 degrees. Getting it wrong leads to a cascade of problems culminating in a wavy or curved trailing edge. I really want to get this step right the first time!