Tail Cone 10-5-1 to 10-6-3

I continued with the tail cone by deburring the edges and lightning holes of the F-1006 bulkhead (the largest bulkhead in the empennage kit that sits behind the baggage area). This bulkhead is split into 4 parts and each is deburred separately.

I then clecoed the bulkhead together and reamed #30 the 8 holes common to the top section of the bulkhead. 

Bulkheads are getting larger!

Next I laid out and marked the 6' and 8' J-channel stiffeners for the sizes specified in the plans, making sure that the lengths were accurate. To mark the cut lines across the stiffeners, I cut a small stiffener piece off one end and used that as a guide to easily draw the lines over the bends.

Using a piece of J-channel as an aid to marking lines across the stiffeners

While marking the 8' stiffeners, I noticed that one of them had an edge that tapered down in width so that at one end the width (of the straight part that sits against the skin) was about 1/8" less than on other stiffeners. I'm not sure if this will be an issue (strength or otherwise), but before I cut the stiffeners, an email is going out to Van's support to determine if this stiffener should be used or replaced.

Notice the width of the stiffener flange on the left is about 1/8" less than the stiffener flange on the right

Van's reply on the narrow stiffener indicated that it should be fine as long as I can meet rivet edge distance requirements (2x rivet shank diameter which I believe I can on the narrower J-channel as long as I am careful placing the hole). Van's also mentioned that these J-channel stiffeners are only there to add support to the skins to prevent/minimize oil canning, and have no structural impact on the tail cone.

So, building on, I double checked my measurements and rough cut all 12 J-channels to the required lengths using the band saw (and a hack saw for some initial cuts on the shorter J-channels that didn't initially fit in the band saw). I cleaned up the cuts to the lines on the disc sander.

J-channel stiffeners cut to length

I then used a small combination square to mark the 45 degree angles on each end of the J-channels, and again rough cut the angles on the band saw, and finished the cuts to the lines on the disc sander.

Using a combination square to mark 45 degree angles

All angles marked and ready to cut

Using the disc sander to trim the 45 degree cuts to the correct angle

I then deburred the outer edges of the J-channels using the bench grinder and a fine needle file to get into corners that the grinder wheels couldn't reach.

Next I used the small combination square to mark the rivet center line along the J-channels. For this I found it easier to support the J-channels by clamping them to wood blocks cantilevered off the edge of the workbench.

Marking rivet center lines 5/16" in from the edge of the J-channel

Once the center lines were marked, I made additional marks 3/16" in from each end of the J-channels. These were now ready for assembly.

All 12 J-channels cut to length and prepped

J-channel end angles all cut, deburred and marked

Before starting tailcone assembly, all that was left was to prepare the two longerons. I cut these to length on the band saw, and then marked the locations of the bend lines and notches.

Longeron marked for notch to be cut

After drilling the holes for the notches, #40 then 1/4", I cut the remaining part using a hacksaw as this was easier than trying to hold the longeron steady in the band saw. I then cleaned up the notches with some medium and fine files, followed by fine aluminum oxide sandpaper. I also deburred the ends of the longerons using the fine wheel on the bench grinder.

Longeron notches cut and deburred, and 2 degree bend line marked

Next I formed the longeron bends by attaching each longeron in turn to the padded vice, with the bend line mark lined up with the end of the pad. Then by applying force in the direction of the bend, I struck the longeron near the mark several times with a rubber mallet. 

I started off carefully, frequently removing the longeron to check the bend angle against the corresponding skin, and I slowly crept up on the correct angle, also making sure that I didn't add any twist to the longeron while hitting it.

The left longeron took longer to bend, probably because I was using my left hand to hit it with the mallet. When I switched to working on the right longeron, the bend angle formed far quicker than I expected, and I was lucky I caught it before I bent the longeron too far! However, everything worked out, and both longeron bends look and fit well against the skins.

Longeron held in vice at the bend line, and struck with rubber mallet to form the bend

Longeron bend was frequently checked against the side skin

Both longerons bent to the correct angle. The bend is fairly subtle at less than 2 degrees.

Build Hints

• Use a small cutoff piece of J-channel as a guide to marking lines across the channel
• A small combination square can be used to easily mark 45 degree angles and also rivet center lines 
• Be careful handling the longer J-channels and longerons. It is very easy to hit unintended objects while moving them around
• Bend the longerons carefully and slowly, frequently checking the bend angle against the skin to make sure that you do not overbend.

Time Taken:     10.5 hours

Dates:                January 23 - January 24, January 29, February 4 - February 5, February 9 2023

Tail Cone Total Time:           23.3 hours

RV-10 Build Total Time:      279.3 hours

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