Horizontal Stabilizer

More countersinking on the Horizontal Stabilizer spars tonight. I finished the rear spar, and got about half way through one side of the forward spar. It’s getting faster, given how much practice I’m getting, but I think I still have another hour to go to finish this step.

I finished deburring and dimpling the HS skins this weekend, and started countersinking the spar flanges where they will accept the dimples. It’s challenging getting a perfect countersink. The goal is to have the top of a rivet be 0.007 inches below flush. Even with a well calibrated countersink, just the slightest hand pressure difference can result in a different amount. I contemplated setting up the drill press, but opted for the hand drill where I can more easily feel what’s happening. The drill press would also be a little awkward given how long the spars are (10 feet). Everything came out ok so far, I’ve finished around 50 of ~400 holes. Once I’m done countersinking I’ll also prime the inside of these holes, as they will be contacting the skins.

The last couple of nights I’ve spent time deburring and dimpling the HS skins. I peeled off the vinyl inside the skins, and on the outside to expose the holes. Deburring is fairly easy, the edges don’t take much to smoothen out, and the holes are all pre-punched to final size. For the holes, a quick debur with the tool is all I’m doing. For edges, I’m using my vixen file to remove bumps, then an edge deburrer, and then a small file. The combination of tools gives a good outcome. I was only able to finish dimpling one side of one skin tonight, I just can’t stay awake any longer.

Tonight I started by addressing an over-sunk hole on the spar. I reamed the hole out to #30 size, then countersunk for a 1/8th rivet. Then I trimmed a 4-5 rivet to 4-4.5, and riveted it in place. This is the very middle rivet on the top of the spar, so it even looks symmetrical.

Then I used a beam-style torque wrench to torque the rear spar nuts to 28 inch pounds. The tool is easy to use for these low torque settings, and apparently sufficiently accurate.

Then I match drilled some holes for the inboard most ribs, then dimpled all the ribs, except for the specific holes that will take screws for the fairings etc.

Here is the forward spar with the inboard ribs clecoed on for match drilling. They are set at a 10 degree angle:

I used the squeezer to dimple the ribs. It was fast and easy.

Stack of dimpled ribs:

I finished up the riveting for the forward spar doubler and caps tonight. A variety of rivets are required due to the various combination of materials getting riveted. Everything came out nicely. I will have to fix one rivet hole that was over counter sunk, probably drilling it out to the next larger size rivet (1/8).

With the priming done, I was able to rivet the spar doublers, spar caps, and the hinge brackets to the forward and rear spars. With my pneumatic squeezer already calibrated (I made a chart with all the various settings), it was a fast and easy set of tasks.

I started by riveting the rear spar doubler. Here it is part way through:

Then I riveted on the hinge brackets:

Then riveted together this part, which contains a bearing:

I clamped it up to keep it square while riveting:

This bolts onto the spar, so I need to get a torque wrench to set these nuts to 28 inch pounds:

Then the forward spar. This has the spar caps, so it’s slightly different. More rivets, and longer rivets. I only got part way through before deciding to take a break for the night:

Following the instructions, I clecoed together a nose and inboard rib and then used it to trace out the shape for the cradle. I had some old particle board shelving, and used that to make the 4 pieces, tracing out the shape onto each one. Then I cut it all out on the bandsaw, cut some aluminum angle for a base, and screwed the angle to the bottom of the cradles, which will allow it to be clamped to the workbench.

Over the weekend my goal is to get all the HS parts primed and ready to start riveting. Depending on timing, I may also get started deburring and dimpling the skins.

I beveled the leading edges of the nose ribs tonight. I also bent two of the nose rib flanges, along with flames fire and aft of two ribs. These rib flange bends are required because the inside edge of the HS skins are angled to follow the shape of the Vertical Stabilizer; at the leading edge the skins are further outboard, and at the aft end they are more inboard. The ribs follow the edge of the skins, so the inboard most ribs are at an angle to the spar, hence the need to angle the flanges.

The front spar doubler sits on the forward side of the front spar, and has a variety of hole patterns. Today I clecoed and final drilled the holes, deburred, and then countersunk twelve holes on the face of the doubler. Then I countersunk the inner most 9 holes on both spar flanges. These will be under the vertical stabilizer and don’t have a skin covering. I messed up on one countersink on the flange, enlarging the hole slightly, probably a couple hundredths of an inch too deep. I’ll look at it again tomorrow, but I may just upsize to a -4 rivet.

Next I’ll be fluting and shaping ribs, and then I’ll prime all of the HS parts, hopefully this weekend.