Tail Cone 10-1 to 10-4-8
While waiting for the elevator trailing edges to cure, I made a start on the tail cone, the first big section of what will become the airplane fuselage.
The first step involves fabricating a tie down bar from a stock piece of extruded aluminum. Part of the fabrication also involves tapping an 8-16 thread to 1-1/4" deep. I decided to tap the hole first prior to trimming the bar, as doing so would allow me to tap the other end if my first attempt didn't go according to plan.
To tap the hole, I first had to updrill it to 5/16" diameter as that is the hole size required for an 8-16 tap. After ensuring everything was perfectly level and aligned on my drill press, I proceeded to drill the hole (at a slower RPM of around 1300) using plenty of cutting fluid. I drilled slowly, backing out the drill a few times to allow aluminum shavings to exit, and the enlarged hole came out perfectly centered.
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| Using the drill press to upsize the hole for tapping |
I then put the bar into my vise and leveled it again, attached the tap, and using a tap guide and cutting fluid proceeded to slowly tap the hole. For every couple of turns in, I backed the tap out half a turn to help expel aluminum chips. Once the tap had gone in several turns, I removed it and the tap guide. I then proceeded with tapping the hole the rest of the way, and I was very happy with how it turned out.
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| Tapping the hole using a tap guide to help ensure that the tap is held in alignment |
After cleaning out the threads with some WD-40, I test fit an 3/8-16 bolt I got from the local hardware store and it went in smoothly. I then finished up this part by trimming it to size on the band saw and deburring all edges on the bench grinder.
Next I grabbed the F-1012 fuselage bulkheads and deburred all the edges prior to clecoing them together. I then marked the tie-down bracket as directed, and clamped it in position on the bulkheads so that the line marks were centered on the appropriate holes in the bulkheads.
Initially I used ratcheting hand clamps to hold the bracket, but this proved cumbersome to place the piece in position for drilling using the drill press. To make things easier, I first match-drilled the 3/32" holes with a 3/32" bit so that I could then place clecoes in those to hold all the parts together.
With the clecoes in place, I was then able to use the drill press to upsize those holes to #30 (#31 bit followed by #30 reamer), and then also match-drill the 3/16" holes.
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| Using the drill press to upsize holes in the fuselage bulkheads and tie down bracket |
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| Match drilled holes nicely centered on the marked lines |
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| Drilling the #12 holes for the nutplates in the Rudder Cable Angle |
I finished up the Rudder Cable Angle by drilling the nutplate attachment holes using my #8 nutplate drill jig and then countersunk them for flush rivets.
I also fabricated a Bulkhead Stiffener, the same length as the Rudder Cable Angle, from one of the 6ft J-channel pieces.
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| Rudder Cable Angle and bulkhead stiffener cut to size and drilled |
Next I grabbed the F-1011 bulkhead and upsized 2 holes for the rudder cables to 5/8" using the unibit on the drill press.
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| Upsized holes for rudder cable |
With that done, I grabbed the two F-1011C Horizontal Stabilizer attachment bars and straightened them using the vise and a rubber mallet. The bars were pretty straight to begin with (to within ~1/16" to 3/32" along their length), but some moderate taps with the mallet allowed me to get them straight to within 1/64" along their length.
I then clecoed the bars together and deburred the edges of both bars together on the bench grinder. Keeping them together allowed me to keep the edges square as I was deburring. Once smooth, I clecoed the attachment bars to the F-1011 bulkhead.
Next I clamped the bulkhead stiffener in place and match drilled the holes from the bulkhead into the stiffener using the pneumatic drill (drilling first to #31, then cleaning up to #30 with a reamer).
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| HS attachment bars and stiffener drilled and clecoed in place |
Finally, I match drilled holes into the rudder cable angle in the same way as the stiffener, with the only change being that I used magnets to help clamp the angle near the ends while drilling the end holes.
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| Using magnets to help hold the ends of the rudder cable angle to the bulkhead |
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| F-1011 bulkhead is now ready for initial assembly of the tailcone |
Moving on to the next bulkhead, I first fabricated a horizontal stabilizer attachment bracket from a piece of 1" x 1" x 1/8" aluminum angle. The ends are angled inwards 5/32", and after rough cutting the bracket on the bandsaw, I finished the edges first using the belt sander followed by the Scotchbrite wheels on the bench grinder.
I also separated the bulkhead doublers and deburred the edges on the bench grinder.
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| HS attachment bracket cut to specified dimensions, and bulkhead doublers separated |
Next I clamped the horizontal stabilizer attachment bracket and doublers in position on the bulkhead and match-drilled the bulkhead holes into the bracket using the pneumatic drill.
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| Horizontal Stabilizer attachment bracket after match drilling to bulkhead |
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| Bracket and doublers attached to F-1010 bulkhead |
As these are laser cut bulkheads, I also reamed the #30 holes common to the attachment points and the F-1085 Rudder Cable bracket.
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| F-1008 bulkhead deburred, reamed and connected with clecoes |
Next I grabbed the F-1007 bulkhead pieces and upsized the two 3/16" holes to 5/8" using the Unibit on the drill press. Clamping these pieces securely is now much easier with the platform I constructed to attach to the cross slide vice on the drill press. The holes were perfectly positioned after drilling.
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| Drilling with the unibit on the drill press. Piece securely clamped! |
The final step to prepare the F-1007 bulkhead for initial assembly involves deburring all edges and final drilling holes common to the two halves. I tackled this in the same way I did for the F-1008 bulkhead above.
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| Deburring of F-1007 edges complete |
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| 5 bulkheads drilled and deburred so far... one more to go for the tailcone! |
Build Hints
- To tap for a 3/8-16 bolt, drill the 5/16" hole about 1/2" deeper than the desired tapped length. In this case for a 1-1/4" bolt, drill the hole to 1-3/4" length and then tap.
- When match drilling and/or upsizing holes, try to first drill the holes to a size where clecoes can be used to hold the parts together rather than clamps. This then gives more options for using a drill press to finish the holes, or better access with a hand drill.
- Ream all holes in laser cut parts even if they appear final sized. Laser cut parts tend to leave more debris in the holes compared to stamped parts.
- Be careful when aligning parts for match drilling. Be sure to check end hole edge distance on the part being drilled into, and start match drilling from the center adding clecoes in each drilled hole. Remove all clecoes periodically while match drilling to clear any aluminum chips/dust that accumulates between the parts being drilled.
- Magnets allow clamping very close to holes being drilled. This is especially useful when holes are close to ends of parts.
Time Taken: 12.8 hours
Dates: January 8 - January 10, January 15 - January 22 2023
Tail Cone Total Time: 12.8 hours
RV-10 Build Total Time: 262.2 hours
Priming Total Time: 26.4 hours (not included in build time totals)