Month: March 2024

Tonight I installed the WAAS GPS antenna. I’m placing the one behind the GA-35 GPS antenna, and offset to the right, just over 12 inches apart.

The process was the same as the other GPS antenna, although this one is slightly larger and has two 5/8 size holes for the connectors vs just one on the GA-35. Using the back-plate (purchased separately from Stein Air) as a template, I carefully selected the right position making sure it was parallel to the longitudinal axis of the airplane, and clear of the sub structure (j channels, ribs, bulkheads). I used the centerline of rivets to ensure it was parallel, and calculated the required clearance from sub structure, then placed it as far aft as I could. This location gave me just over 12 inches distance edge-to-edge from the two GPS antenna.

I drilled and reamed the holes, and used the step drill to step up the two large holes to 5/8.

Deburring the inside of the holes and then stripping the primer from the underside of the top skin was a challenging step. I had to climb into the baggage compartment then reach back to complete the tasks, which was doable with enough patience.

Dimpling the holes in the skin was also a challenge. I had to use my pop-rivet dimpler, which doesn’t give the best results on a good day, because there’s no other way to access both sides of the skin. I used a step stool to get up off the ground, and then I found I could reach back enough to inset the nail into the hole, and support it while putting the pop riveter into position. it was fiddly, but not hard.

I made quick work of the necessary countersinks, installed the nut plates, and then pop riveted the backplate into position.

I used some silicone and the rubber gasket to install the antenna.

Tonight I installed the first of two GPS antenna. This was the GA-35 and provides GPS signal to the G3X system. The second GPS antenna provides WAAS signal to the IFR navigator.

I purchased the backing plate from Stein Air, and it was great to have to mount holes pre-cut. I could then use it as a template to locate the holes on the fuselage skin.

I started by marking out the rivet holes that will hold it onto the skin, then I drilled the rivet holes into the backing plate. Then I taped the backing plate to the fuselage and carefully measured to get it square to the airflow, and at least 12 inches from the other antenna I will be installing, while also free from interference with substructure.

With the template in position I drilled all the holes into the skin. I carefully reamed all the holes to get it as accurate as possible.

After cleaning up the holes, I dimpled the skin, countersunk the backing plate, and installed the nut plates.

Then I was able to clean primer off the inside of the skin, and rivet the backplate on. With that done, I put a bead of silicone around the edge and torqued the screws to 16 inch pounds per the spec.

Tonight I was able to install both comm antenna, and was surprised how easy it was. I bought the Rami bent whip antenna from Vans, and am installing two because I have two radios, the GTN-750, and a second, remote radio.

Vans ship the quick build with pre-cut holes for a smaller two-bolt antenna, but the doubled plate they install is fastened with 4 rivets that are in the exact location of the 4 mount bolts for the Remi antenna. This makes it easy, simply drill out the rivets, remove the doubler, install a new doubler, and mount the antenna.

The antenna ship with a doubler, which seems somewhat undersized, but I’ve used it anyway. If it ends up cracking, it’s easy enough to undo the nuts, take it off, and make a new one.

I had no issues drilling out rivets, drilling the center hole, and installing the antenna by myself. I used the rubber gasket, and a bead of silicon between the rubber and the aircraft skin, just in case.

I started on the passenger side, then did three pilot side. No issues on either side.

Having more-or-less finished the shelving behind the panel, I moved onto the antenna installation. I ordered the antenna I needed from Vans and Stein Air; 2 comm antenna, 2 GPS antenna, and one ADS B antenna.

I started with the ADS B transponder antenna which mounts under the tail. I had already final-sized the holes when I built the tail cone, but I had also primed in and around the holes. I spent time removing the primer to allow the antenna to connect to the ground plane.

With the primer removed I started work on a backing plate. I’m not planning to rivet the backing plate in place, I’ll secure it using just the antenna bolts. This isn’t quite as solid, but I really don’t want to rivet the backing plate in place. Since I can’t prime the parts, and this is at the bottom of the tail, there’s a chance of corrosion in this area. I’d rather be able to quickly replace the backing plate in the event corrosion occurs in this area.

With the plate made, I was able to easily install the antenna myself as access to both the inside and outside at this location is easy. I placed a bead of silicon to seal the gap.