Tail Cone 10-13-3 to 10-15-2, 10-16-6 to 10-17-2

It was now finally time to begin match drilling the aft deck to the tail cone frame. I began by making sure that the center line on the F-1010B spacer was still visible through the aft deck holes, and then drilled those 4 holes using a 1/8" bit followed by a #30 reamer.

Next I match drilled the side holes of the aft deck into the longerons. I first made sure the clamps were keeping the longerons in line with the edges of the aft deck. I added an additional clamp at the longeron bend because I saw that the longerons were being pushed out slightly, so the clamp helped bring everything into alignment. I drilled the holes with a 1/8" bit, alternating between left and right, forward and aft sides to avoid imparting a twist, and clecoed each holes as I went. Once all holes were drilled to 1/8", I finished them with a #30 reamer.

For the 2 holes at the forward most end of the aft deck, and the 2 holes next to the Horizontal Stabilizer attachment bars, I used a 6" #30 bit to match drill the holes due to the extra reach needed.

I then enlarged the outer holes next to the F-1010B spacer to #12. I decided to enlarge the holes in stages as I found it easier than going directly to final size, so I used a #28, #21, #17 bit and finally a #12 reamer. I used the pneumatic drill for these holes, but found that it had issues with torque, especially going through the thicker pieces with the larger bits. However the holes came out nicely in the end, especially with the reamer.

All aft deck holes match drilled to longerons and F-1010B bulkhead

Next I centered and clamped the Support Angle in place and match drilled the holes using the 1/8" bit and #30 reamer. I did the same with the Up Elevator Stop.

To upsize the outermost holes in both these pieces to #12, I decided to temporarily remove the Horizontal Stabilizer Attachment bars to give me more room to work. I also first countersunk the #30 holes slightly with the deburring bit to ensure a smooth start to upsizing.

This time I also used a corded power drill to upsize the holes and it worked perfectly. No torque issues with this drill, and from now on my plan is to use the power drill (space permitting) whenever drilling holes larger than #30.

Outer holes countersunk slightly before upsizing

HS attachment bars removed and outermost holes upsized to #12

Now that the aft deck was fully match drilled to the frame, I removed the top skins and stiffeners, and proceeded to mark the locations of the Shoulder Harness Anchors on the longerons. After deburring the edges of the anchors and making sure they were in the correct orientation, I clamped them in place. I then match drilled each hole in turn into the longeron using a #17 bit followed by a #12 reamer. This resulted in nice, round holes, and as each hole was drilled I inserted an AN3 bolt to ensure the holes were kept in alignment. After drilling was complete, all anchor holes were deburred.

Working on match drilling the Shoulder Harness Anchors

Next I tackled final drilling the cover plate attachment holes (4 in each) into the side panels to #28. This was easy enough, but I found that I had to hold a block of wood behind the skin while I was drilling to support the aluminum. My first attempt without the wood had the power drill zip through the hole, and I was lucky that the hole did not suffer any damage. As the holes were drilled, copper clecos worked well enough to hold the #28 holes in alignment.

After drilling, the cover plate edges and holes were deburred.

Upsizing the cover plate attachment holes

A few more tasks left before tail cone disassembly, the first one being drilling the holes for the static ports. I have decided to use the Dynon Pitot Static Kit, as it provides a pair of nice looking flush mounted static ports that appear to work well (based on reviews) as well as all the hoses and connections required for plumbing the static lines. 

Installation of the ports requires the static port skin holes to be upsized to 1/2", so after first drilling the two holes to #30, I used a handheld drill with the unibit to upsize them to 1/2". I did first practice on a scrap piece of Aluminum to make sure that I was able to control the size of the hole because this was the first time I had used the unibit with a handheld drill rather than the drill press. It worked very well, and I ended up with two nice round static port holes perfectly sized for the protruding part of the ports.

Drilling 1/2" holes with a handheld drill for the two Dynon static ports

Happy with the static port 1/2" holes in the skins

Static port fits perfectly in the hole

I then marked the triangular portion of the forward end of the F-1037-R side skin that will need to be cut off after the tail cone is disassembled.

Next I skipped ahead a page and started preparing the battery channel. After separating and deburring the F-1036 parts with the band saw, belt sander and bench grinder, I final drilled the 1/4" and #12 holes using reamers where required. The #30 and #40 holes were already final drilled so I left those alone. I then did the same with the F-1035 Battery/Bellcrank mount.

Reaming battery channel parts on the drill press

The drill press was also used to ream through holes that needed to be in alignment

Final sized and deburred battery channel parts

The battery/bellcrank mount also requires countersinking of various holes for nutplates. Most of these were done on the drill press, but I used the pneumatic drill for the 4 holes on the tab.

Countersinking the tabs on the battery/bellcrank mount

Battery/bellcrank mount final-sized, countersunk and deburred

I am planning to install Garmin pitch, roll and yaw servos for the autopilot and have already purchased the mounting brackets and hardware. This was a good time to check positioning and fit of the pitch and yaw servo mounts, as they attach in the tail cone at the aft end of the battery/bellcrank mount. 

The yaw servo mount is held in place with rivets where it attaches to the bellcrank ribs, and I verified that the holes were all already final sized to #30. The remainder of the brackets are held in place with bolts and I used a few to hold the brackets in place while checking that all the holes lined up.

Fitting the Garmin pitch and yaw servo mounts at the aft end of the battery/bellcrank mount

Servo brackets looking aft...

...and looking forward

I then deburred the holes and edges of the servo brackets as they had a few sharp corners.

Garmin servo brackets deburred and ready for priming. Pitch servo mount is on the left, yaw servo mount is on the right with a spacer that goes under the pitch servo bracket.

The final step before disassembly of the tail cone involved separating the F-635 Bellcrank parts and deburring the edges. I then clecoed the bellcrank together and final drilled the #30 and #12 holes using reamers in the pneumatic drill.

Bellcrank clecoed, deburred and final sized

With all prep work done I disassembled the entire tail cone. Now on to deburring and dimpling!

Tail cone fully disassembled into a lot of parts...

...and even more parts

Build Hints

• Use a power drill, if space allows, to drill holes larger than #30. A pneumatic drill tends to cause the drill bit to catch on the hole edges or slow down in thicker material due to lack of torque.
• Consider using a block of wood for support when match drilling Aluminum sheets, especially when drilling near edges where an edge is not supported in other ways.
• Do not use a corded (high torque) power drill for smaller holes, or with the unibit, due to the difficulty of controlling the drill even while trying to manage the drill speed. A smaller handheld battery powered drill is easier to control, and also to hold due to its lighter weight, although it will take a little longer to drill through the sheet metal.

Time Taken:     8.8 hours

Dates:                March 6 - March 12 2023

Tail Cone Total Time:           73.9 hours

RV-10 Build Total Time:      329.9 hours

Priming Total Time:                     26.4 hours (not included in build time totals)