Empennage Attach 11-8-1 to 11-9-1
While waiting for Van's to provide additional guidance on the use of laser cut parts (of which I have some in my wing kit that I haven't yet worked on), I decided to continue with a few small tasks that were originally planned for later.
One of the tasks involved building the elevator trim mount that will go in the tail cone. The details of this are outlined in Section 11 - Empennage Attach, and involves first fabricating 2 sets of attachment brackets out of aluminum angle.
First off are the trim bellcrank brackets that are fabricated from a piece of 3/4"x3/4"x1/16" angle. I started by marking out both bracket hole positions, but quickly realized that the only way to ensure the holes matched and were in line was to first drill both holes in one bracket, and then use that bracket as a guide to drill the holes in the other bracket.
 |
| Bellcrank brackets marked on aluminum angle prior to drilling... |
 |
| ...after which I decided to drill one bracket first and use it as a guide to drill holes in the other |
The 1/4" hole was first drilled on the drill press using a D bit, and then reamed to 1/4". The 1/8" hole was also drilled on the drill press to ensure it was perpendicular to the surface. The brackets were then cut to rough size on the bandsaw and finished with the disc sander and deburring wheel.
 |
| Finished bellcrank brackets ready for match drilling to the elevator trim mount |
 |
| The plans have the brackets drawn to scale, so it was satisfying to see that both brackets, laid over the drawings, had the holes in the exact positions depicted |
I then did a test fit of the bellcrank brackets to the bellcrank in the trim mount. The AN4 bolt went in nicely, and the washers fit in place easily. Rotation of the bellcrank was smooth, but a little tight. I'll decide later if I need to use thinner washers (or file down the washers I have) as described in the plans.
 |
| Bellcrank brackets clecoed in place with the bellcrank... |
 |
| ...the bolt slides through nicely, and there is no binding with rotation of the bellcrank although it is a little tight |
Next I worked on fabricating the Trim Cable Anchor brackets from a piece of 1"x1-1/4"x1/8" angle. I started by marking the hole positions, and then marking points on the radius around the 7/16" hole center.
 |
| Hole locations marked for the trim cable anchor brackets |
The 7/16" hole was first drilled to 1/4" on the drill press, and then the unibit was used to increase the diameter of the hole to its final size. Since the angle is 1/8" thick, I had to make sure there was adequate clamping to ensure that the angle didn't move while being drilled.
Also, because the unibit steps are 1/8" wide, I found that I had to flip the angle over after drilling from one side, and then drill the other side with the unibit to make sure the 7/16" hole was the same diameter on both sides.
 |
| Using the step drill bit to enlarge the bracket holes to 7/16" |
 |
| All holes drilled in their proper locations |
Once all the holes were drilled, I used the bandsaw, disc/belt sander and deburring wheel to cut the brackets to final size. I also deburred all holes as needed.
 |
| With the holes drilled, I marked out the bracket dimensions |
 |
| Finished brackets came out nicely, and are ready for match drilling to the trim mount |
Next, I started working on the elevator trim mount and associated pieces. First I had to round over the forward sides of the trim servo spacer so that it would fit flush inside the mount bracket. This was done with the deburring wheels, and I made sure that I maintained adequate edge distance for the corner holes in the spacer.
 |
| Elevator trim mount parts. Blue film had been removed from the bellcrank previously while test fitting to the fabricated brackets. |
 |
| Rounded side edges on the trim servos spacer |
I then clecoed and carefully aligned the trim cable anchor brackets in place, ensuring they were parallel to the mount cutout and with eachother, and then match drilled the attachment holes through the mount.
 |
| Brackets clecoed and aligned in place |
 |
| Mount held in vice while match drilling holes into the trim cable anchor brackets. Holes were clecoed as they were drilled. |
I also did the same with the bellcrank brackets. After clecoing and aligning them, I used clamps to hold them in place while match drilling the first holes. Once I had two clecoes in place, I was able to remove the clamps.
 |
| Clamps keeping alignment of brackets while matchdrilling |
The final step before priming these parts was to countersink the cable anchor bracket mounting holes in the trim servo spacer, and also the nutplate attachment holes in the mount bracket.
Next, I prepped all the parts for priming.
 |
| Countersunk #30 holes in the trim servo spacer |
 |
| Countersunk #40 nutplate attachment holes in the trim mount. This material is thinner, so I had to hold a backer behind the hole to capture the countersink pilot as I had done on previous parts |
Next, I prepped all the parts for priming.
 |
| Parts wiped down with acetone and ready for priming. I also threw in the wing tie down brackets into this priming batch |
 |
| Elevator trim mount parts cleaned and etched before primer |
 |
| Elevator trim mount parts curing after priming |
After letting the primer cure for a couple of days, I started riveting the trim mount parts together. I started by riveting the nutplates to the trim mount bracket, but found that I had countersunk a couple of holes a little too deep and the rivets did not sit well. I have a new trim mount bracket on the way from Van's and will redo this part once it arrives.
Since the trim mount bracket is 0.04" thick (at the threshold between dimpling and countersinking), I think I'll dimple the nutplate attach holes and nutplates on the new bracket rather than countersinking as the plans called out.
For now, I was able to rivet just the trim servo link.
 |
| Trim servo link |
Build Hints
- Fabricating brackets where hole positions need to be matched horizontally and vertically, drill the holes in one bracket as accurately as possible, then use that bracket as a guide to drill holes in the second bracket.
- If using the step drill in thicker material, use as many clamps as needed to hold the drilled piece rock steady. Also if the hole thickness is approaching 1/8" you may need to also drill from the other side to clean up the hole and make sure it is the same diameter all the way through
- Check aluminum thickness prior to countersinking. If it is at the threshold of ~0.04", it may be better to dimple the holes to avoid any issues with countersinking thinner material
Primer used: ~20g + 2g distilled water
Time Taken: 5.9 hours
Dates: August 15 - August 24 2023
Empennage Attach Total Time: 5.9 hours
RV-10 Build Total Time: 451.5 hours
Priming Total Time: 47.2 hours (not included in build time totals)