As Dave Nadler says, a vertical antenna "disappears". when focused at infinity - as long as you have two eyeballs and the antenna is dark colored, the brain doesn't pay any attention to it.

As to making the antenna out of very thin wire; from my Nave ET days, a thin antenna element has a more narrow bandwidth. Since flarm uses a frequency hopping protocol (I think from 885 to 915 Mhz), thin may not work very well.

Like Rex Mayes (Williams Soaring), I made the mount for my PF as a shelf that sits just aft and slightly below the glareshield. Power lead goes through a small hole in the top of the glareshield, then through a male to female in-line coaxial plug connector (Amazon - 5.5mm X 2.1mm, commonly used for CCTV) to allow clean canopy jettison. If the canopy goes away it takes the PF with it.

bumper