Side skins for the tailcone...                              

Once again I was completely convinced that the F-1280 skins wouldn't fit (wrong again). I hung them in the cutouts and started clecoing from the highest point down. It was clear that I couldn't eliminate the gap between the skins and the tabs on the bulkheads near the bottom already-riveted F-1281 skins. It wasn't even close. I removed all the clecos, started with the bottom row of clecos (lowest one on each bulkhead, then the next lowest, etc.). Amazingly, it all cinched up tight! I need to quit doubting the guys at Van's. These CNC-punched skins are incredible. 

 I would be nice if the instruction manual suggested that the builder start at the bottom and work his (or her) way up.  In some situations they do say where to start and which way to go with the rivets.  Not so with clecos.  It absolutely wouldn't work the first way I tried it.

(page 10-03) Tail cone....                    

Finally a large part.    Well, the stabilator is limited to 8 feet  in order for the airplane to be trailerable on public roads, so I suppose that qualifies as big.  Not like the tail cone, though.

The first thing I did was discover an error (small) in the build manual (in Fig. 4, page 10-03 the labels on parts F-1284-L and F-1284-R are switched).  I checked the revisions, and found none for that page.  My RV-12 is the 593rd kit shipped, so all the other people who built tail cones earlier had to have discovered this error.  I e-mailed Van's and they replied with a three-word e-mail: "You are correct."

In trial fitting the curved pieces which attach to the left and right bottom skins (F-1281), I was at first convinced  they wouldn't fit.  Everything else has been a perfect fit (CNC is a wonderful thing).  I discovered, however, that if I started clecoing at the lower row of holes (with the skins upside down -- the holes closest to the saw horses) at each bulkhead, everything pulled into place as I worked my way up.  I could then cleco the long rows at the top of the curves.

Then came my favorite part: using the pneumatic rivet puller.  To my eye, those long rows of rivets are a thing of beauty.  The rivets within seven inches of the foward edge are left open for the attachment to the fuselage (still in the box).

When inserting the 1/8th-inch rivets through the holes in the aluminum sheet, the #30 holes through two or three sheets sometimes don't line up, preventing insertion of the rivet.  The holes are of the correct size, but the smallest misalignment of the sheets makes it impossible.  The clecos fit but the rivet shanks don't.  One option is to run the #30 bit through again, but I worry about chips between the sheets of aluminum.  I solved this problem (in 99% of the cases) by putting a slight taper on the end of a 1/8th-inch drift, then running this into the holes.  Twisting the drift helps.  This seems to pull the holes into alignment enough for the rivet to fit.

The edge-brake (break) tool discussed in an earlier post worked perfectly.  The slight down angle (2 or 3 degrees) made the long edges of the lap joints (the long rivet rows shown above) perfectly tight.  Leave the Blue Plastic Hell on while using the tool.

Stabilator trial fit....                                

Supergluing the washers to the stabilator bearings turned out fairly well.  I cut the head off the same-size bolt, leaving a shaft length of about three washer thicknesses.  I could then put the washer over the bolt stub, dab on some superglue, insert the stub into the hole, then remove the bolt stub.  This centered the washer perfectly and allowed me to put uniform pressure on the washer while the glue set.  The bearing is on the back side of the bulkhead shown here.  The bulkhead moved through the correct range relative to the stabilator, hitting the stops properly.  I was surprised at the small angle through which the stabilator moves.  I'll pay attention next time I preflight the Cherokee and estimate the angular range through which the stabilator on that airplane moves.

 (page 10-04) Pneumatic rivet squeezer.......                            

For the first time, I understand why people bought one.  Building the aft-most bulkhead required a bunch of squeezed 1/8th inch rivets.  As you can imagine looking at the picture, many of them were hard to reach regardless of squeezer type.  The Main Squeeze from Cleveland Tool that I bought uses the same arbor as the pneumatic job, so that would have been an issue no matter what.  Of the 75 or so rivets, I had to drill out about five.  Realizing that I have to drill out a rivet usually results in a string of expletives that would do a drunken sailor proud.

I do, however, realize and appreciate the importance of this piece:  The stabilator attaches to those two ears protruding from either side from the flat surface.  I understand why Van's went with a stabilator for the -12, but when I put on my engineer's cap and ponder that pesky aero-elastic phenomenon called flutter, I wish they'd gone with a fixed horizontal stab with elevator.  I'd be willing to bet that the stabilator along with the loads it's capable of putting on the tail cone are what limits the Vne to 135 knots.  Considering that I learned to fly in a Cherokee (43 years ago!) and jointly own (along with 19 other guys) a Cherokee 235, I'm no stranger to stabilators.  They just have good and bad points.

Trial fitting this piece to the stabilator turned out to be a PITA.  The washers have to be super-glued into place in order to do the assembly, and so far, each time I try I knock one of the washers loose.

(page 10-02) Tail cone soon....                                         

The saw horses are constructed and the skins for the tail cone are identified. The first uncertainty arose when the instructions said "..break the edges.." on the appropriate pieces. The word probably shoud be brake rather than break, but that's beside the point. On the large skins for the tail cone, the edges which go on the outside in the lap joints need a two or three degree bend to ensure that the edges lie flat after riveting. I discovered copious discussion of this topic on the forums, with no clear consensus on how this should be accomplished.

 After considering and rejecting several methods championed by various builders, I discovered this at Cleveland tool and ordered it.  A few trial runs on scrap went well, so I'll try it on the actual skins.

Spring semester is over and grades are turned in, so I have a whole week free before summer school begins.  I hope to put in a lot of building hours.  Teaching first summer session will totally obliterate five weeks of my life, but I need the $$$ in order to persue hobbies such as airplane building and old Corvette restoration.  The DMV is once again threatening to revoke the registration for my antique if I don't get it inspected within the next month or so.

(page 09-10) Nutplates and counterweights.....                                


After reading the horror stories on the forum about stripped threads in nutplates, it was with fear and trepidation that I installed the control horns on the box spar. With the box spar all closed up and the stabilator skins attached, it occurred to me that if the threads in one nutplate stripped, I'd be screwed. There's no way to reach the inside of the box spar. 

A fair number of builders on the forum advocate running a tap through the threads prior to running the bolt in.  My gut feeling is that this would negate at least part of the self-locking feature of the nutplates.  Having bolts back out of the elevator control horns could ruin your whole day (picture a smoking hole in the ground).  The torque required to turn the bolts in the flattened part of felmale threads varied from 3 to 10 in-lbf among the eight bolts on the control horns.  I added this to the published torque spec (20 - 25 in-lbf in the case of AN3 bolts) to get the value to which I torqued each bolt.

By contrast, the counterweights attached with no issues.  The tail cone is next.