Riveting Of Tail Cone Fairing Nutplates Completed – Almost

Over the past few days there have been just a couple of very short work sessions, but have been able to finish dimpling all the nutplate rivet holes on the tail cone. Fortunately, access was good and all twelve nutplate rivet holes on the lower portion of the tail cone were dimpled using the pneumatic squeezer.

Riveting tail cone fairing nutplates onto the lower portion of the tail cone.

For riveting the nutplates, I choose to use a no hole yoke because it offered more clearance for riveting the nutplates on the upper portion of the tail cone in the vicinity of the rudder horn and rudder cables … it worked out quite well.

The no hole yoke sets the rivets without the use of a die on the yoke and is also shaped differently so it offers more clearance.

All the nutplates on the lower portion of the tail cone are now installed.

The four rivet holes that needed to be dimpled using the C clamp will need to be riveted using a rivet gun because of clearance issues. Of course, one could always remove the vertical stabilizer and the stabilator and there would not be any issues. I have elected to work around them so will use a rivet gun and bucking bar to set the remaining four rivets … the two rivets closest to the vertical stabilator and the two rivets closest to the upper skin of the stabilator.

Using the rivet gun and bucking bar to rivet the nutplate rivet closest to the vertical stabilizer.

Was able to finish off setting all of the rivets for the nutplates with the exception of the two closest to the stabilator. Because of the location, did not feel comfortable attempting to do this by myself, so will enlist Bernie to give me a hand later today to set the remaining two rivets thus putting this chapter of the build to rest.

Dimpling Tail Cone’s Nutplate Holes Presents Challenges

Although a relatively short work session did made some forward progress on the nutplates for the tail cone’s fairing despite running into a few clearance problems. Work this session involved drilling the rivet holes for the six nutplates that secure the upper half of the tail cone’s fairing. The drilling of the nutplates for the upper half of the tail cone’s fairing was accomplished using the same drilling methods covered in the previous post for the lower half of the fairing.

This portion of the tail cone’s skin is flat, so drilled the nutplate holes from the outside using the angle drill outfitted with a #40 drill bit.


After all the rivet holes for the nutplates were drilled, they need to be marked for positioning then removed for deburring and dimpling … this was done one nutplate at a time so labels did not need to be made. Marks were placed on one of the nutplate's rivet holes in the tail cone's skin and the corresponding rivet hole on the nutplate to identify positioning for reassembly. I quickly ran into issues when attempting to dimple the nutplate rivet holes closest to the vertical stabilizer … the pneumatic squeezer could not get onto the rivet because the squeezer’s yoke interfered with the rudder’s horn. I tried a couple of different yokes to no avail and a hand squeezer …. shy of removing the rudder (not an option), nothing seemed to work. After a little brainstorming, came up with the idea to set the dimples using a C clamp.

Because there was not enough clearance to use the pneumatic squeezer for setting the dimple in the nutplate rivet hole closest to the vertical stabilizer, opted to use a C clamp to compress the dimple dies together. Although a little scary, took it slow and this method ended up working out quite well.

After using the C clamp to squeeze the dimple dies together, the dimple was checked with a rivet … this rivet is sitting flush with the skin … time to move on. The red marking denotes nutplate positioning for reassembly.


Working from the top down, the nutplate rivet holes in the tail cone were dimpled along with the corresponding nutplates. All was going well until reaching the lowest rivet hole closest to the stabilator. Even with the pneumatic squeezer sitting on the skin of the stabilator, there was not enough room to get the dimple dies close to being squared up … so resorted to using the C clamp again to make the dimple.

The C clamp was once again enlisted to create a dimple … this time for the nutplate rivet hole closest to the stabilator.

Did not have the time to finish off all the dimpling so will finish that off during the next work session. I can see now riveting the nutplates onto the tail cone skins at the tight spots may present a challenge … sure all the tail feathers could be removed to allow for unobstructed access, but would prefer not going that route if I can find other methods that work.

Com Antenna Short Wire Issue Resolved – Tail Cone Drilled For Nutplates

Following a suggestion from friend Mike, decided to try using a 90 degree BNC connector first as opposed to tearing out the entire center tunnel to gain access to the com antenna wire. Mike made the valid point lots of airplanes have 90 degree adapters (including his) so it should work just fine and will alleviate the need to move the com coax forward.  The 90 degree connector will add approximately .2db of signal loss to the antenna which in the grand scheme of things is not all that much. Fortunately, one of the local FBO’s had a spare connector for me to purchase.

This 90 degree BNC connector will eliminate the need for the elusive “cable stretcher” or tearing out the center tunnel to gain access to the com coax cable so it can be moved forward.

The 90 degree BNC connector installed on the back of the Garmin GTR 200 radio’s frame. This should only add approximately a little less than a quarter db of insertion loss.

Back to work the tail cone fairing … with the tail cone fairing still secured in position with Clecos, the #40 holes in the fairing were match drilled to a final size of #27 into the tail cone’s skin. All twelve mounting holes are drilled to #27.

Match drilling the tail cone’s fairing into the tail cone using a #27 drill bit.

While the fairing was removed for deburring, a little more filing and sanding was done to tweak the stabilator’s upper and lower skin … now there should be a 1/8" gap between the tail cone’s fairing and the upper and lower stabilator skins.

The tail cone’s fairing is secured onto the tail cone using 12 screws that screw into nutplates. The nutplates offer a little bit of a challenge because there really is not much room for drilling the tail cone’s skins for the nutplates from the inside out. Van’s suggests bending the nutplates to conform with the curve of the tail cone's skin then drill using a long #40 drill bit … but I found that would place the drill bit at quite a bit of an angle for most of the holes.

A nutplate secured with a screw and a pile of washers ready to be drilled from the inside out.

I opted to get a little creative and used the 90 degree pneumatic drill. For the most part it worked well there was still a small angle but not as much as using the long #40 drill bit.

Using the pneumatic angle drill outfitted with a #40 drill bit to drill the nutplate rivet holes into the tail cone’s skin.

There were a couple of holes where the angle drill was hitting  stuff which created either a bad angle or total interference ... so for those locations, elected to drill one of the holes from the inside and use the drilled hole to Cleco a spare nutplate curved to conform with the outside of the tail cone’s skin so the second hole could be drilled from the outside. This worked out well. Because one hole was drilled from the inside and the other from the outside it should make the angular difference minimal even though it is on a curve ... especially after the holes are dimpled.

This nutplate location had one hole drilled from the inside … then a spare nutplate was curved to match the contour of the tail cone’s skin and secured on the outside of the skin with a Cleco so the second rivet hole could be drilled from the outside.

After all the rivet holes for the nutplates are drilled, the nutplates are to be marked so they can be placed back to the proper locations after removal for deburring. The builder also needs to identify two nutplates that will receive a little more attention … in that, a tap is to be run half way through them prior to being riveted in position.

The two nutplates my fingers are pointing towards require a tap to be run half way through them prior to being riveted. I’m guessing this is done because these two nutplates are fairly close to the stabilator’s bottom skin and this will make screwing the screws into the nutplate a little easier.

Tweaking The Tail Cone’s Fairing & Stabilator

Being at a temporary impasse when it comes to moving forward with the instrument panel, decided to continue making forward progress and work on the tail cone’s fairing while waiting for the center panel section.


Last fall when preforming the initial fitting of the tail cone’s fairing, Van’s plans suggest there should be at least 1/8"of clearance between the fairing and the stabilator and also between the trim actuator pushrod and the slot in the fairing. The clearances were less than optimum, so at that time marks were placed on the fairing and the stabilator skins where material would need to be removed. A Dremel outfitted with a sanding drum was used to remove the excess material followed by a file and sandpaper. The initial cuts on the fiberglass were made outside and unfortunately had to be completed inside when the forecasted monsoons cut lose.

Some material was removed already with the Dremel outfitted with a sanding drum. This still needs a little more work.

Using the Dremel from below to remove material from the stabilator so the sanding drum could not inadvertently skip across the stabilator’s skin. It was raining so hard outside the noise level in the hangar was deafening so ear protection was necessary.

Tweaking the gap between the slot in the fairing and the trim actuator pushrod.

There is still a little tweaking left to do, but it is almost there. Once the clearance issue is resolved, the twelve #40 holes in the fairing at the aft end of the tail cone need to be drilled to #27 and nutplates installed.

Anti-Servo Trim Motor Installed

The first task of the day was installing the safety wire for the anti-servo trim tab’s hinge wires. There are two small holes in the center of the aft spar on the horizontal stabilator that are used to capture both trim tab hinge pins with safety wire.

The safety wire for the hinge pins is run through two holes in the stabilator’s aft spar and looped over the hinge pins for the left and right anti-servo trim tabs to secure them in place. Note: The discolored metal is not corrosion ... it is from the SanChem metal treatment (similar to Alodine but eco friendlier) that was done to the inside of the skins.

The safety wire for the hinge pins is twisted tight on the forward side of the stabilator’s aft spar.

The trim motor assembly is attached onto the tail cone’s aft bulkhead using a long AN3-35 bolt and a couple of spacers. Nothing difficult, but everything is a tight fit and the work is done from under the horizontal stabilator, so it takes a little finessing to get all the components in place.

Placing the trim servo motor tray in position so the mounting bolt and spacers can be installed.

One thing of note:  Builders should pay close attention to the AN3-10A bolt called for attaching the trim servo push rod onto the horn on the trim tabs. The bolt is just a little too long as can be seen in the photo below, so it will be necessary to add an additional washer or use the next size shorter bolt. The DOG Aviation procurement department purchased an assortment of bolts just to have on hand so will likely need to look in that parts bin. The short term fix will be adding an additional washer, but during the first annual plan on replacing the bolt with a shorter bolt.

As can be seen in the photo, the AN3-10A bolt called for in the plans is a tad long .. the nut would have bottomed out on the unthreaded shank of the bolt.

Adding an additional washer took up enough space so the nut did not run out of threads while being tightened.

Return from the future: I did not like the way the bolt looked because there were more threads showing beyond the nut than the one to three threads the "standard" calls for. Decided to rearrange the washers on the bolt for a better instillation. The resulting instillation used an AN960-10 washer under the head of the bolt and in addition the AN960-10 washer that goes under the AN-365-1032 lock nut, I added an additional AN960-10L washer. The AN960-10 washers on either side of the MM3 bearing were left undisturbed. The result is a perfect fit and the instillation looks much better now.

Results after adding an AN960-10 washer under the head of the bolt and adding an AN960-10L washer under the nut.

Having the trim motor in place and connected to the anti-servo tabs it was time to operate the trim motor through its range of motion to check for free operation of the horizontal stabilator along with checking clearances. All was well.

Of note to other builders: I did not play around with the micro connector as suggested in the plans for a location to place voltage on the trim motor’s white wires. Instead, applied the power at the end of the servo cable in the instrument panel. Reason for this was two fold … first, did not want to mess with applying power to the pins of the delicate micro connector at the servo motor end and possibly damage one of the tiny pins. And secondly, I had not yet operated the trim motor to determine which of the two white trim motor wires ran the trim tab up or down when a positive voltage was placed on it … and this information is needed when installing the trim cable’s wires into the connector. Now I know and marked the wires accordingly. Also, did not bother using a bulky 12 volt battery … a 9 volt transistor radio battery works just fine to operate the trim motor throughout its full range of motion a few times.

After cycling the trim motor a few times and checking for clearances and freedom of movement, the plans instruct the builder to use two wire ties to secure the trim motor cable onto the servo tray. The first wire tie just loops through the small hole adjacent to the wiring connector and the second wire tie is to loop through the first wire tie and then around the servo cable to hold it in place. Doing this holds the wire just fine … but doing so also draws the cable onto the edge of the metal servo tray. Not wanting the servo cable to ride against the servo tray, decided to create a standoff by cutting a small piece of vinyl tubing and looping the wire tie through the tubing. The first loop of wire tie is run through the hole as per the plans and the vinyl standoff was attached onto that loop.

My finger is pointing to the standoff made by using a small piece of vinyl tubing to keep the servo cable off the servo tray. This is a much better way (IMHO) of securing the cable to the servo tray than the method called for in the plans.

After verifying the anti-servo trim tab was working correctly and all the clearances were good, moved onto installing the tail cone’s fairing for final drilling. The fairing needs to placed in position and then centered as best as possible between the stabilator’s skin so the final drilling of the fairing’s mounting holes into the tail cone can be completed. The goal stated in the plans is to have the fairing centered as best as possible and then verify there is at least a 1/8" clearance between the fairing and the stabilator.  In my case, it will involve filing/sanding away some aluminum from the stabilator skin. The loss of clearance and ultimate interference is mostly along the aft portion of the fairing as can be seen in the photo below.

The sides have close to the specified 1/8” clearance between the fairing and the stabilator skin but the same can not be said for the aft portion of the tail cone fairing.

The above interference should be easy to address with the aid of a sanding drum on a Dremel tool and a little filing at some point in the near future.

Work Begins On Installing The Trim Servo

Work was suspended on finishing up the tailcone fairing after the two innermost holes on the left side of the upper and lower tailcone fairings were drilled into the tailcone. Basically, after the two holes are drilled the builder is to install the stabilator and then pivot the tailcone faring to obtain an equal spacing around the stabilator then final drill the remaining holes.  I decided to take a pass on doing that until the rudder cables are installed and the trim servo assembly is installed.

After drilling the two holes in the tailcone fairing, with a warm drill in hand, finally got around to finishing the drilling of the holes in the bottom fuselage skin for the access to the landing gear bolts. After finishing up on that, decided now would be a good time to begin working on the trim servo assembly. The trim servo instillation begins with riveting doublers onto the servo tray. AN470AD4-4 solid rivets were used in place of the standard LP4-3 pop rivets.

Riveting F-1287J doublers onto the F-1287A servo tray with AN470AD4-4 solid rivets in place of pop rivets.

The Ray Allen trim servo is placed in the servo tray and is sandwiched by two doublers. The mounting flange of the servo only has 4 mounting holes so Van’s has the builder drill the two center holes in the doublers down through the mounting flange on the servo then use screws and nuts to secure the servo in the tray.

Ray Allen trim servo secured to servo tray with Clecos.

Match drilling the Ray Allen servo to establish two additional mounting holes.

Once the trim servo is mounted in the tray, the tray receives two plastic bushings along with the F-1287 link. All three of these bushings are to be filed down to the point they are just barely protruding the metal.

The bushing in the F-1287 link has been filed down … the two bushings in the servo tray will both need to be filed down the same way.

Once finished with filing the bushings down, work on the pushrod assembly was begun. The pushrod assembly requires the associated hardware be installed prior to match drilling. The F-1287E pushrod has four holes in it which the F-1287D clevis plates are to be Clecoed. The associated hardware also needs to be installed to hold the positioning as the remaining eight holes in the clevis plates are drilled into the pushrod.

F-1287D clevis plates secured into the F-1287E pushrod with Clecos. The hardware for the pivot points (where the castle nuts are located) is temporarily installed to hold positioning during match drilling of the pushrod.

The next step tomorrow will be drilling and riveting the assembly.
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