Elevators

My goal tonight was to rivet the trim tab spar onto the bottom trim tab skin, so I can work on gluing the ribs in place over the weekend. On the inboard end of the trim tab, the trim tab horn is riveted onto the outside of the skin, and in two places it shares rivets with the spar. I started by back riveting the spar, and everything was looking good. I left out the two rivets that are shared with the horn, and then came back to them at the end (masked over area in the picture below).

Because the horn is on the outside of the skin and it protrudes out, I decided to squeeze these rivets. The horn is in two parts, so I riveted on the first one, then started on the second. After setting the second of the three rivets, I gave it a quick inspection and realized that the first two rivets had twisted and on one, a small crack had opened up on the side of one of the dimples (bottom left rivet below).

Unfortunately I’ll need to order a new skin, and will need to remove the 30-odd rivets I set tonight.

I’m not yet 100% sure why this happened, but my guess is that for some reason the horn was not completely flush with the skin. Then as the rivets set, they pulled the skin and horn together, causing the skin to bend up on one side. The horn couldn’t bend with the skin because it was sitting flush against the other half of the horn that was already riveted. As I remove all these rivets, I should be able to confirm the issue.

When I do this again, I’ll try to back rivet these on the corner of my back rivet plate, which is likely to produce a better result.

Tonight I scuffed the trim tab skins and spar with some 150 grit sandpaper. I did this where the foam ribs will be glued down, and along the trailing edge where the wedge will be taped into position. The scuffing helps the glue adhere to the metal.

I started by masking the areas I needed to scuff, then carefully scuffing with sandpaper. Because I had already primed the spar, I needed to remove the primer in the areas where the ribs will be glued to the spar. Just a small dab of acetone on a terry towel was enough to break down the primer. With a few careful wipes the primer was gone and I was able to scuff the spar.

I used some more acetone to clean the sanded areas, then removed the tape. Finally I dimpled all the remaining holes in the skins, and they are now ready for riveting and glueing.

I countersunk the trim tab trailing edge wedge, and the trim tab spar, then dimpled the bottom side of the trim tab spar.

I was able to quickly complete the trailing edge wedge countersinking tonight, since I set up the drill press last night.

With that done, I switched countersinks and calibrated it back to a depth of 0.007 inches below flush. Then I spent some time figuring out the best way to countersink the trim tab spar. I ended up drilling a series of holes along an edge of particle board, so that the clecos could sit inside, slowing the spar to sit flush on the board. It also helped to lock the spar in position. It was then easy to countersink, with great results.

Then I dimpled the bottom flange of the trim tab spar. But before I could do that I needed to find my narrow diameter male and female dimple set. I knew I had them yesterday, but just couldn’t find them anywhere. Eventually I decided to check the trash bin, and sure enough I found the male dimple die in amongst some old rags! Digging deeper I found the female die. I need to take care not to do stupid things like throwing away my expensive tools 🙂

Today I worked on the elevator trim access doubler and the trim pushrod arm.

After dimpling several nutplates, I riveted them to the access plate doubler. I squeezed the rivets, but in hindsight it might have been better to back rivet these. The very thin material means that it twists very easily, and i had a couple of less than perfect rivets, one of which I ended up drilling and removing.

Then it was on to the pushrod arm. This is made of 3 pieces of aluminum riveted together. The internal piece is shorter than the two outside pieces forming an attach point in each end. At one end, the outside pieces are also pre-bent to provide a wider opening for a wider part to attach.

The outside pieces need to be countersunk, and then flush riveted. This is quite straight forward except for the one hole closest to the bent parts. The bends mean that the part doesn’t sit flat, and the countersink cage contacts the surface unevenly. I used some scrap and made a couple of shims to use to accommodate the bends, and to support the opening at the end.

Riveting was fairly easy, I squeezed the 3-3.5 rivets, while being careful to only squeeze the rivet and not the material. The shop head is small inside the countersink, but wide enough to form a very strong bond. I’ll touch up the prime on this part again before wrapping up the elevators.

Next it was on to the elevator trim tab. I dimpled the closeout tabs, clecoed it together, drilled the close out tabs, marked the trailing edge wedge and skins, put a break in the skin trailing edges, then trimmed the trailing edge wedge. I set up the drill press for countersinking the trailing edge, then decided to stop for the night.

Today I had a few hours in the garage, and was able to get through a number of steps. I started by countersinking the trailing edge wedges, then countersinking the left rear spar, then dimpled a bunch of parts.

I used the Cleveland Tools wedge drilling jig, which made this a painless operation.

On the last hole of the right elevator wedge, I applied too much pressure and slightly elongated the hole. I’m going to leave it and build on, since all the other holes are good.

Countersinking the rear spar for the trim tab hinge was also quite easy. I clamped down the spar and went slowly. Because the spar is sandwiched between the skin and the hinge, countersinking the thin material is acceptable. The holes become slightly elongated, and there is a knife edge, but that is by design in this case. I deburred the holes carefully, trying to round the knife edge just slightly.

Then it was a few hours of dimpling; spars, ribs, shear clips, plates… basically every part that needs a dimple is now dimpled. A couple of holes were hard to reach, and I ended up using my vice grip dimpling tool, including the forward flange of this rib.

Next step is to rivet some nut plates to the inspection plate doubler.

Tonight I started dimpling parts. I made it through the counterweight skins and the four elevator skins. It’s a satisfying job, and so easy with the DRDT-2, I don’t know how others manage with a c-frame and mallet.

I started by breaking the trailing edges of the skins, so they will lay flat when riveted in the final step. I used my hand roller tool, which was way better than fiddling around with the hand seamers. The tool has two small wheels, and is clamped to the edge, one on each side. One is set to a slight angle. You clamp it to the edge, then draw it along, and the edge bends slightly. I wish I had used this on the rudder, it would have saved me some time.

Dimpling the skins is pretty standard stuff. However, the trailing edges require a narrow die, which I had purchased some time ago. The training edge is bent to fit flush with the trailing edge wedge, and the regular dimple die would interfere with the bend. The narrow die is ground down towards the tip, so it can dimple in some tighter places.

Tonight I completed the last few things I wanted to do before priming all the elevator parts. I shaped the outboard edge of the right elevator trailing edge wedge using the belt sander. Then I deburred the spar doublers, then trimmed and deburred the last couple of brackets. I have a big pile of smooth parts ready to be cleaned, etched, then primed.

I trimmed my replacement rear spar, then deburred it. I used a hacksaw to cut off the excess 11/16 of an inch, and then filed it down to final shape.

Then I was able to assemble the right elevator and final drill the few holes that need it. These are the gusset that joins the rear spar to the inboard rib, the tip rib web to main spar flange holes, and then the elevator horn holes. I also measured and trimmed the trailing edge wedge, using a hack saw and then filing down to final size with the vixen file.

The next step is to sand the outboard trailing edge wedge to match the shape of the fiberglass tip. Then I’ll disassemble the right elevator, and debur the few remaining parts. That should set me up for priming this weekend, then it will be on to dimpling.

Deburred skins today, then separated the three pieces of the trim tab pushrod and deburred them. This was a skip ahead, but wanted to get this done so I can prime it along with the other parts. The pushrod is made up of three pieces that are riveted together, here’s a picture of the right hand side piece. They are fairly small pieces, and eventually need to be countersunk.