For the past week I’ve been preparing to install the upper skins of the rear fuselage, which will close out most access to this section. Although there is an inspection panel mid-belly, I decided it would be easier to install the GMU 11 magnetometer before closing out, so earlier in the week I ordered a G3X standard LRU kit from Aircraft Spruce, which includes the GMU 11 as well as the GSU 25 air data computer / AHRS, so it was a bit pricey. Luckily, Aircraft Spruce is still shipping normally right now, so I wasn’t delayed in receiving the part. The magnetometer is installed with brass screws, which are non-ferrous; this reduces soft-iron errors in the magnetic sensor. I also pinned and assembled the connector for the GMU 11.
I completed a few other wiring tasks as well. I terminated the RG400 wiring for the VHF comm antenna that goes on the roof, using an BNC connector that I got from Aircraft Spruce. For this task , I bought an inexpensive crimping tool from Amazon. The crimp came out nice, and my DMM confirmed no shorts.
I also installed a red strobe light for the belly, which will act as a beacon / anti-collision light. I am using a Whelen Vertex VTX609 super-LED light, which is designed for use in police cars (for example), but they are small, very bright, easy, and far less expensive than the products that are marketed for airplanes. These lights are mounted from the inside, with a standard 1 inch diameter hole, and two screws mounted on a 1.25″ diameter circle. Rather than drill a hole in the skin of the plane, I modified the rear-most inspection panel to hold this light. Pascal Latten designed and made oval skin doublers last year to use in the wings for the smaller inspection covers. I really liked them, so I asked him to send me a few for my wings too. I decided to use one of them, to create the screw-mounted inspection cover / LED mount – it works great!
Because I am installing a recovery parachute, there are some holes in the top skins that must be dimpled prior to installation. There is a blow-away panel that goes over the chute, so the rivets below this panel must be flush. The fuselage manual indicates which holes to dimple, but it neglects to identify a bunch, so I had to refer to factory pictures for which holes to dimple. Along with the LRU kit, my recent order from Aircraft Spruce also included an Avery dimpler tool, which has the dimple dies welded onto a pair of locking pliers. It looks weird, but it works well.
The front 75% of the skins installed well, with holes lining up just about perfectly. The rear 25% were a different story, with the holes not lining up very well, especially on the last rib before the tail section (rib 601). I’m not sure why the fit was so poor, but I took a reamer to the holes to make it work. On the last rib (rib 601), I even had to drill a few new holes because the holes were so far off. Some of this is possibly due to the fluted edges, which the computer model probably doesn’t account for. I have riveted on nearly all of the starboard-side skin, but only about 33% of the port-side skin… even though it’s installed and looking OK, I want to think about the holes I had to ream out. I’m considering upsizing the holes to 4.0mm.