Interesting home-brewed investigation into the drag between the fin-type and rod-type transponder antenna by one of our friends in The Netherlands.
Seems like the fin type antenna - unless mounted exactly on the centerline of the glider, where the flow is expected to be parallel - may produce a lot of turbulence and drag.
https://www.youtube.com/watch?v=8ii_...ature=emb_logo
Take a look at this type of antennae installed under the belly of power planes. In most cases, you will find one side (typically the right side due to the prop-wash)) caked with soot and grime while the other side is relatively clean. Would be interesting to quantify the drag this causes and the extra fuel burn over the lifetime of the plane. I bet most power-pilots don't even know/think about it.

Uli
'AS'