For my Fohdy I wanted 1.3 GHz video for the range and because the band is allocated for amateur radio use, so I can legally operate there. However most 1.3 GHz antennas are quite large, and I was concerned about the effect of additional drag on this relatively small (40″) wing. So I decided to use the True RC Singularity 1280/58 antenna, which is very small for a 1.3 GHz circularly polarized antenna and comes in a side-fed version that I could embed within the wing to minimize drag. I ordered one in December to take advantage of a holiday special, and although it was shipped promptly it only arrived today courtesy of the snail paced South African postal system.
I had originally planned to put the antenna quite far out on the port (left hand) wing. However it has a fairly short (5″) coax and I didn’t feel like splicing it, so I moved it close enough to the electronics compartment for the coax to feed in comfortably. I tested the thickness of the wing at this location by pushing pins through the foam, and determined that at the thinnest point it was about 27mm thick, about 4mm thicker than the antenna is tall. I decided to fit the top of the antenna flush with the upper surface of the wing, so the markings will be visible and to allow as much foam below the antenna as possible, since this is where the wing is most likely to be dinged. The aerofoil is fairly flat towards the trailing edge, so it shouldn’t have much effect on the aerodynamics.
I traced around the antenna on the top surface of the wing and cut a cylinder out of the wing with a narrow bladed craft knife. Cutting from the top ensured that the surface where the antenna will be flush is the correct size to fit it. Before removing the cylinder I drew straight pencil lines on the top and bottom, which extended onto the surrounding foam, to serve as orientation marks so I could fit it back correctly.
After removing the cylindrical foam cutout, I used a tent peg heated with a blowtorch to bore a tunnel inside the wing from the electronics compartment to the antenna cutout. I had to widen the tunnel by making a circular motion with the tent peg to get the SMA connector through. I glued the antenna in with some Shoe Goo (having run out of Goop, which is not available here), using pins to hold it flush with the top surface of the wing. I cut about 23mm (just less than the height of the antenna) off the top of the foam cylinder, sliced away further thin slivers of foam until it fitted flush on the bottom of the wing, and then glued it in.
Singularity 1.3GHz Antenna Installation
This picture shows the location of the antenna, and how it sits flush with the top of the wing. The picture below shows the installation from the bottom – you can just make out the location of the antenna on the left, roughly in line with the coax that enters the electronics compartment.
Bottom View of the Antenna Installation
While I had the aircraft on the bench I also added an extra spar on the bottom of the wing abut 5mm in front of the electronics compartment and running between the two leading edge spars. Because my wing has such a large electronics compartment, I was a bit concerned about whether there was sufficient material remaining to hold the two sides of the wing together in a crash. The rear spar runs just behind the electronics compartment, so that’s fine. However the two front spars meet at the front of the aircraft, potentially a weak point. There’s thick Coroplast on the top of the wing, but only the thin electronics compartment lid on the bottom, so I decided to reinforce the bottom with a 2mm carbon fiber rod. Probably unnecessary, but better safe than sorry!