It is possible to eliminate the vertical antenna, yet have vertical
polarization. I was going to install one on my motorglider, but eventually
installed a simple vertical. My motoglider is fabric and not ideal for the
flush mount antenna.

The flush mount antenna is described as a flush disc with annular slot. It
is described in John Kraus's book "Antennas". He designed the first of the
antenna arrays that probe outer space.

Basically, the 1/4 ground plane antenna is replaced with a top loaded
vertical. The top of the vertical is flush with the fuselage and the base
is 1/4" below the surface. The diameter of the disc is about 3". This disc
is the top loading for the shortened 1/4 wave antenna. In addition, there
must be a ground plane at the bottom of the hole.

It would be a good antenna for a plastic airplane - if you are willing to
cut about a 4" hole in the fuselage and then run a ground plane on the
surface about 6 inches in each direction.

It could be molded into a plastic airplane.

To this point, I do not know anyone that has done so and of course no one
makes them. Perhaps it is used in the Stealth aircraft, but generally they
are the last pilots who have a transponder on.

Instead of going to all that work, I opted for a standard quarter wave
antenna. It was destroyed during a less than ideal landing in 3 foot weeds.

Colin