This update covers work over the last few days as its been piece meal work after daytime commitments. Since the baggage and rear seat floors will be going in and restrict access to the rear rib bays, some work has to be done prior to closing up these areas.
I plan on mounting two bent whip style antennas under the fuselage for the VHF voice communications. A popular place seems to be under the rear seat area on the second inboard bay on each side. To support the antenna, provide a mounting platform and reinforce the skin a doubler is needed to beef up the area. Following the recommended practices, the doubler should be at least the thickness of the skin it is reinforcing. Additionally, it should tie into the ribs. Since, mounting to this location will require going OVER the rib flange of one rib, you can either use a special tool to “joggle” the metal to bend over it, or as I did, I used two reinforcements. In the pictures below, there are two doubler styles, the green method is the better method of the two and is what I used. I first placed a flat spacer that is the same thickness of the rib flange (.025″) and then used a .032″ piece with a bend flange itself to attach to the other rib’s webbing. To accomodate this, I first had to drill out the rivets in the flange of the rib I would be going over.
Once I drilled out the rivets, I match drilled the pattern I put into the doubler, deburred and riveted platenuts onto the doubler. I had to use a pop rivet dimpler to dimple the fuselage skins to accept the AN426 flush rivets to attach the doubler. Prior to final riveting of the doubler I applied a coating of No-Ox from Home Depot (prevents oxidation and improves long term conductivity of electricity to ensure good antenna performance. I applied this to the doubler and then cleco’d the plate into place. Of course as we riveted, a small amount was squeezed out.
I had to of course get Tricia to help rivet these as I scooted underneath and we shot these rivets. I was then able to test fit the antennas on both sides and they fit great! Once the plates were in, I got my ohm meter and checked the resistance between the doubler plates (and it’s nutplates) and the airframe. The install manual says .003 Ohms between the antenna baseplate and the ground, but I haven’t installed my antennas yet and when I measured from the nutplate to the ground, it was a higher resistance at .2. So I am going to have to do some research to see what is going on. Perhaps once the antenna is on, the measurement will be much more realiable.
Once the doublers were done, I finished running the conduit to the tail. It’s not a good practice to just run the conduit to the tail and leave it flapping around. In fact, everything in a plane should be secured to prevent braking or abbrasion. So I fabricated some mounting plates to go across the lightening holes in the bulkhead to the tailcone and put a 3/4″ hole in each and ran the conduit to the plate to mount it in place. I also fabricated one for one of the baggage floor ribs so I could run the battery cable conduit over one bay to be closer to the battery box area so that cable wont have to go across the tail to get to a conduit. I also put a smear of proseal on the conduit where it went through a mount or routing hole in the airframe to secure the conduit to the hole. I also epoxyed some tie-wrap mounts to the baggage floor ribs to secure the conduit as it went along the floor area between the bulkheads to keep it secure as well. I wrapped the conduit in silicon tape to provide extra protection against the tie-wraps.
It was then onto prepping the floor panels for installation. The baggage floors got some stiffners back riveted into place and the inspection hole frames were also riveted into place along with nutplates for the inspection cover itself.
Prior to putting the floors in, I went ahead and ran some of the cable that was sitting in the tailcone waiting for the conduit to be ready. I wanted to make sure I could snake the thick battery cable up ok with the curves in the conduit, plus it would get it out of the way in the tailcone. So I got the VHF antenna cables, battery cable as well as the static air tubing and the pitch servo trim wiring ran up to the front of the fuselage, tagged and ready for when the panel gets wired up and installed. Some epoxyed supports will be needed along the way where the cable exits the conduit in the front of the fuselage, but that can come later.
I also drilled holes to route the VHF antenna cable to the seat floor area. The area right in front of the passenger seat bottom and the rear of the seat well area has a cover that will go in to cover up the flap controls, so this is a good area to run extra wiring that wont be seen. I got some 375-3 bushing which is a perfect and snug fit for RG400 cable. Drilled a hole in the side panel as well as the bulkhead leading into the seat bottom bay. Extra cable will be put into a service loop for future maintenance needs.
I then made up more insulation for the areas to be covered up. As with the pilot area, 1/4″ rubber insulation was coated with contact cement, a layer of HD aluminum foil and another layer of insulation. This was then cut to fit the bottoms of the seat bottom and baggage rib areas. I also cut panels to attach to the side panels of the area to be closed up with the floor panels.
I finally got the floor and seat panels cleco’d into place and began to set the rivets. These are all hand squeezed pop rivets and after a while your hands get fatiqued putting the torque on the tool to pop these rivets, luckily there aren’t all that many that need to be done. The inspection covers look like they will work. They wont allow the step bolts to be removed as I knew they wouldn’t, but I can get in there, inspect things and tighten the assembly as needed. If I need to remove the bolt, I will drill the floor as Van’s plans call for.
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