On Saturday, December 30, 2017 at 2:58:29 PM UTC-8, OHM Ω http://aviation.derosaweb.net wrote:
I am resurrecting this old post as some pilots I know are installing transponders this winter. The key questions are the location of the antenna and the type to use.

1) Does the blade type antenna provide "better" coverage than the rod type? What about aerodynamics between the two?


The blade antenna is a rod antenna encased in plastic, they all have the same RF performance.

2) Potentially dumb question - Ground Planes - It was mentioned above by UH that the ground plane should be on the outside of a CF glider. As carbon blocks RF transmission is it considered conductive? If conductive, and grounded to the avionics, can the CF constitute a ground plane? I saw another RAS thread on this same subject without a clear consensus given.


Follow the directions of your glider manufacture. A proper aluminum grounding plane behind the carbon fiber will provide a better ground than relying on the carbon fiber alone, and manufacturers will be recommending to do that. "Considered conductive" and actually how good a connection to the ground you can make and the impedance of/to that ground at 1GHz you don't know....

Stop trying to overthink stuff, just crack open a manufacture's TN (or one close) and follow the instructions. In the case of an A&P IA signing off on any work I would hope they expect that to have been done.

Installations of antennas requiring ground planes in a carbon fuselage without a separate ground plane is counter to guidance provided in AC No: 43.13-2B. Your A&P, or anybody else working on an aircraft, should be aware of this.