Final Preparations For Tail Cone Mating

Yesterday was a long and busy day at hangar 45 … but productive. The list of items needing completion prior to mating the tail cone with the fuselage was completed.


The final routing of the Tygon tubing for the AOA (angle of attack) sensor was decided upon. There were two tooling holes that grommets were placed into … one in the lower aft edge of a F-1223 baggage rib and the other in the F-1206A bulkhead. This worked out perfectly … when the tubing passes through the grommet in the F-1206A bulkhead it immediately meets up with the wiring harness in the tail cone going to the ADAHRS. This will work out great. The Tygon tubing will be secured to the bottom skin by a dollop of silicone.

Final routing of the Tygon tubing for the AOA sensor in the ADAHRS. This path places the Tygon tubing well below the torque tube for the left flaperon when it gets installed.

Once the Tygon tubing passes through the F-1223 baggage rib it makes an immediate bend aft and passes through the F-1206A bulkhead to join the wiring run to the ADAHRS in the tail cone.

After the AOA routing was finalized, the tail cone was slowly worked closer to the fuselage but canted at an angle so there was still access into the tail cone to work on the wiring and plumbing for the Dynon ADAHRS. The excess pitot and static line was worked forward along with the trim wiring cable and all the wires running to the ADAHRS unit were worked aft through all the loose wire ties. Once all the ADAHRS wiring was pulled aft, the heat shrink tube was shrunk down over the wires and the plastic DB connector shell was screwed together using nonmagnetic brass hardware substituted in place of the steel hardware shipped with the connector. Next the the static air tubing was cut and the “Y” was installed.

Tail cone was worked forward to the fuselage and canted to allow access into tail cone to mount the ADAHRS unit and attach the “Y” for the additional static air tube going to the instrument panel.

The “Y” installed in the static air line so static air can be routed forward to the instrument panel for the backup instruments.

The DB connector was screwed onto the Dynon ADAHRS unit along with the temperature probe connector and then the ADAHRS unit was installed in its mounting fixture on the roof of the tail cone with the supplied nonmagnetic hardware. Note for other builders: … the screws supplied were black so they did not look like brass or anything nonmagnetic at first glance. A magnet was used to verify they were nonmagnetic during kit inventory.


After the ADAHRS unit was secured to the tail cone the pitot and static air line tubing was attached onto the ADAHRS unit using the supplied connectors. These connectors although bulky are really easy to use and really only need to be hand tightened. The instructions say the nut can be tightened further by going 1/4 turn beyond hand tight by wrench if desired … I desired, so that is what was done. Next the Tygon tubing for the AOA port was attached finalizing the instillation of the Dynon ADAHRS unit.

Tightening  the static air and pitot fittings 1/4 turn past hand tight with a wrench completes the instillation of the Dynon ADAHRS unit.

Completed Dynon ADAHRS instillation ... just needs a few wire ties.

The last item that needed completed prior to mating the tail cone to the fuselage is installing the left and right fuselage side skins.

Pealing off the blue protective coating from the right fuselage skin to ready it for riveting after the tail cone is attached.

 

Left fuselage skin in place and ready for riveting.

It was after midnight when the side skins were finally on the fuselage  so called it a night. The late night push was because friends are going to help with the mating of the tail cone tomorrow so needed to be ready.

Preparations For Mating Tail Cone To Fuselage

This work session involved finishing up the bending of the tail cone’s tabs to the prescribed angles and chipping away at the list of tasks remaining to be finished prior to the mating of the tail cone with the fuselage ... which is slated for later this week. Bending the remaining tabs was not hard, but is a little time consuming if striving for near perfection.

Fellow builders following the DOG Aviation Blog know I have gone off the reservation a tad by running the ADAHRS wiring and pitot plumbing prior to mating the tail cone. This was done in the hopes of being able to mount, wire and plumb the ADAHRS unit and install the ADS-B antenna without needing to crawl inside the tail cone to do so. So far it has been working out … but will know in a day or so when attaching the tail cone onto the fuselage if this was all folly or a really good idea.

Once the task of bending the tail cone’s tabs was completed, moved on to installing the ADS-B antenna mounting plate on the bottom skin of the tail cone. The mounting plate was drilled and primed just before winter’s deep freeze gave DOG Aviation the one two punch.  The rivet holes on the antenna doubler plate were cleaned of any primer along with the area around the two mounting holes that secure the antenna onto the tail cone.  Removing the primer from around the antenna’s mounting holes is quite important because the two antenna mounting studs supply the ground to the antenna. The antenna doubler was riveted into position with four rivets and the antenna bolted in place and torqued to 20 inch pounds.

The ADS-B antenna and the antenna mounting doubler plate. To insure good grounding, the primer has been removed from the doubler plate in the area where the antenna will be bolted to the doubler plate.

The next order of business involved spraying some rattle can zinc chromate primer on the tail cone at those locations where the tail cone's skins will be overlapped by fuselage skins. Some of the overlapped areas were already primed correctly with the much better Akzo primer … but the sides downward and bottom were overlooked when they were primed long ago. Unfortunately, priming the areas now became somewhat of a time consuming task because it required completely masking off the tail cone to prevent over-spray. The parts I missed long ago consisted of the forward edges of the F-1282-L&R bottom skins, F-1281-L&R lower skins and F-1280-L&R side skins.

After masking the tail cone to minimize over-spray, the areas of the tail cone that will be overlapped by the fuselage skins were primed with a zinc chromate primer.

While the primer was drying, decided to prepare the Dynon ADAHRS unit for instillation by installing the fittings for the static air, pitot and AOA lines. Because of not being sure if thread sealers would affect the nylon fittings over time, opted to use Teflon tape on the threads of these fittings.

The Dynon ADAHRS unit with fittings installed and ready to be bolted in place in the tail cone.

Because the DOG Aviation RV-12 will have backup steam gauge instruments requiring a static air source, it will be necessary to tap into the static air line prior to the ADAHRS unit. The DOG Aviation procurement department found a neat “Y” fitting at Stein Air for the nylon static air tubing. The static lines just slip into the fitting and lock in place … the fitting does not require any tools. Each port has a ring that can be pulled back to release the tubing should that ever become necessary.

This “Y” fitting will tap into the static air supply so an additional static air line can supply static air to the instrument panel for the back up instruments. The "Y" will be inserted in the static air source just ahead of the ADAHRS unit.

Ran out of time so will install the "Y" and Dynon ADAHRS unit during the next work session.

Bending Tabs On The Tail Cone Assembly

In preparation for mating the tail cone assembly to the fuselage felt now is a good time to bend the tail cone's tabs per the plans. Much the same as the closeout for the wings, the tabs on the tail cone assembly that will mate to the fuselage assembly require bending to various angles. Depending on the location of the tab, the plans have the builder bending the tabs 10, 9, 8, 7, 6 or 3 degrees.

The original plan was to use the digital level to establish the angles … but it was quickly realized that due to the flexi nature of the mouth of the tail cone that was not going to be a good option. Finally settled on using the digital level to mark the required angles onto a piece of cardboard, and then carefully cut out the pieces from the cardboard to use as a gauge.

Pieces of cardboard cut to be used as angle gauges for bending the tabs on the tail cone per the plans.

Technical difficulties: This paragraph will only apply to those who have dimpled the tail cone for flush rivets. The plans suggest bending the tabs on the tail cone using the same bending tool fabricated for bending the closeout for the wings. This tool will not work on the DOG Aviation RV-12 because the rivet holes in the tabs have already been dimpled for flush rivets. During the winter I gave this issue some thought and came up with what seems like an easy and eloquent solution to the problem. Another bending tool was fabricated with a much wider slot. A thick piece of aluminum flat bar 3/4" wide was cut and a hole carefully drilled and machine countersunk to create a spacer. The location of the countersink is such that when the spacer is placed under the dimples on the tail cone’s tabs, the spacer sits flush with the outer edge of the tabs. The slot cut into the bending tool is the same 9/16" depth as the original bending tool however the throat is opened up so when the metal spacer with the countersink is sitting under a dimple, the tool barely slides over the tabs on the tail cone. This worked out great for bending the tabs … so for those that have dimpled for flush rivets this is a viable option for bending the tabs on the tail cone.

Modified bending tool with a mouth just wide enough to accommodate the thickness of the tail cone tab and the countersunk bar stock spacer.

Using the modified bending tool is easy … just place bar stock spacer under the dimple in the tab. This creates a flat surface for the bending tool to work with. Next slide the bending tool over the tab and spacer then begin bending to the desired angle. Zooming in on the photo below one can see the countersunk spacer under the tab being bent.

Using the modified bending tool with countersunk bar stock spacer to bend one of the tail cones tabs.

By the time the modified bending tool and spacer was fabricated, didn’t quite have enough time to finish bending all the tabs … so will finish up that task during the next work session.

Service Bulletin 14-12-06 Finally Completed

The weather cooperated nicely Friday … the early morning rains gave way to what I believe may have been the first 70 degree day of the year. Taking advantage of the late afternoon warmth and favorable breezes, a small batch of Akzo primer was mixed up and sprayed onto the new replacement pieces for the bearing bracket brace using the air brush. The wet parts were placed into the heated paint drying box and allowed to dry all day Saturday.

Today the freshly primed F-1206F-1 bearing bracket and F-1206J-L&R angles were secured together with Clecos per the plans and riveted together. A small change was made to the Van’s supplied AN470AD4-4 rivets. Those rivets looked a little short to me ... a quick measurement using a rivet gauge verified my suspicion so a slightly longer AN470AD4-4.5 rivet was used to secure the pieces together.

The rivet gauge shows that the increased length of the AN470AD4-4.5 rivet is the perfect length for this location.

Riveting the F-1206F-1 bearing bracket brace onto the F-1206J angles using AN470AD4-4.5 rivets in place of AN470AD4-4 rivets.

Completed new bearing bracket brace assembly ready to install in the fuselage.

Once the bearing bracket brace assembly was riveted together, it was time to install it in the fuselage. Wow! This is a tight fit. The ribs to the left and right require flexing a little to allow the bearing brace assembly to slide into position. Another testament to Van’s quality control … once in position, the new assembly fit perfectly once all the holes were properly aligned. Riveting the assembly was uneventful and only took a small amount of time.

Riveting the bearing bracket in position using the supplied AD4-6 rivets.

Completed installation of the new improved bearing brace assembly which completes service bulletin 14-12-06.

F-1206F Bearing Bracket Finally Removed

Between some tool delays and Mike pulling me out of retirement for a couple of weeks to help him with a large project for his company, it has been a long time since any work has taken place on the RV-12.

Today work resumed by way of removing the remaining rivets holding the F-1206F bearing bracket onto the F-1206A bulkhead. As mentioned in a previous post, I had used solid rivets to attach the bearing bracket to the F-1206A bulkhead which has complicated matters somewhat because, for the most part, the rivet heads are hidden when positioned for drilling. Adding to the quagmire, it was discovered the body of my inexpensive angle drill was too big and would not allow a drill bit to get square to the rivet heads of the outer most rivets on each side of the F-1206F bearing bracket.

As such, I was worried that drilling them out may present problems … so I had a tool specially made to shift the odds in my favor and also picked up a used pneumatic angle drill which has a much smaller body at the drill attachment point. The DOG Aviation procurement department made a call to Mike at Cleaveland Aircraft Tool requesting fabrication of three drill guides to fit over the head an AN470AD4 rivet. The guides were made with #30, #40 & #50 holes through the center and measure 1" x 1/2". Because the rivets were so close to the bend of the metal it was necessary to grind off a little of the guides so the guide would sit square over the rivet heads. The guides worked great and the rivets were easily removed without creating elongated rivet holes.

One can see how much smaller the head of the pneumatic drill is compared to the plastic one.

The three drill guides Mike at Cleaveland Aircraft Tool made worked great.

Drilling the solid rivets was a two man job … so Bernie came over to help. Bernie positioned the drill guides over the heads of the rivets by reaching through the lightening hole in the F-1206A bulkhead as I directed the drill bit through the center of the drill guide and drilled through the rivet … (while trying not to drill Bernie’s fingers). A #50 hole was drilled through the rivets first, then the holes were enlarged to #40. Finally a #30 drill bit outfitted with a drill stop was used to remove the heads of the rivets. Thanks Bernie … couldn’t have done it without your help.

Bernie holding a drill guide over the head of one of the solid rivets as position the pneumatic angle drill bit through the centering hole on the drill guide.

F-1206F bearing bracket removed from the F-1206A bulkhead clearing the way for the new bracket.

The new replacement parts for bearing bracket require a little cutting on the band saw. The piece of predrilled angle that comes with the kit needs to be cut in half and becomes the F-1206J-L&R bearing bracket angles. Another band saw cut is required to remove 1/4" from one side of the angle.

The replacement bearing bracket angle prior to separation.

New replacement F-1206J-L&R bearing bracket angles after separation and trimming.

Before instillation feel it best to prime the new parts and touch up a couple of scuff marks made while removing the old parts. Rain is in the forecast for tomorrow morning so hoping I can get the airbrush out later in the afternoon or on Saturday so the parts will be ready to install over the weekend ... finally putting this portion of the project to bed.