Hi, Steve!
I made all of the antennas for my Lancair; com, VOR, glide-slope, and
transponder. You can make a simple 1/2 wave com or VOR dipole out of
sheet aluminum shaped like a bow-tie. The experimental ones I made had
a VSWR of less than 1.2:1 over the full 108-136 range. By making them
very wide, their electrical length can be much reduced. You can feed it
either into the center using a clamp-on ferrite over the feed-end of
the coax to act as a balun, or feed in from one element-end toward the
center. In this mode you keep the coax up against the antenna, but
insulated from it, and cover the coax the length of the element with a
length of aluminum formed in a "V" cross-section. This serves as a
"bazooka" balun. The balun is very critical in both maintaining
BALanced-to-UNbalanced conversion, and to keep antenna currents from
flowing down the coax back toward the radio. These currents can often
get into the microphone feed and cause squeeling and distortion during
transmit.
The 1/2 wave dipole is a real performance increaser over the 1/4 wave
dipole over a counterpoise, so-called ground-plane. We generally have
insufficient width of the counterpoise to maintain good radiation
patterns down to horizontal angles. With this deficiency, along with
mounting an antenna on upper rather than lower surfaces where the major
radiation is upward, keeps us from having good long-range
communications. You are fortunate in having non-conductive construction
which allows you to place an antenna inside the structure. The com is
vertical polarization, and if you still use VOR, that is horizontal
polarization. Be sure to keep the antenna as far from vertical (com) or
horizontal (VOR) metallic surfaces such as tubes, cables, wires, and
struts as these can contribute re-radition which will form lobes in the
pattern with resulting signal nulls at different aspect angles. Make
each element about 15" long, tapering from 1/2" wide at the feed to
about 12" wide at the end. They can be either triangular or
sector-shaped, in other words straight or curved ends. Separate the
feed ends by about 3/8". Attach the shield to one feed end and the
center conductor to the other. The material I used was 0.010" aluminum
flashing obtained from the local hardware store. Simple, huh?