Drag of Transponder Antennae compared

On Tuesday, February 9, 2021 at 9:14:09 PM UTC-5, India November wrote:
On Monday, February 8, 2021 at 11:06:31 PM UTC-5, AS wrote:
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'
Yes, theoretically the streamlined aerofoil section has a lower drag coefficient than a cylinder oriented at right angles to the airflow. However, the rod antenna has a smaller frontal area, and also if the aerofoil is misaligned with the local airflow it will disturb the flow and cause drag.

Ok - here is a follow-up question/challenge: The aerodynamic resistance of a cylinder vs. a tear-drop shape is about 10:1. How about a 3D-printed airfoil shape like a simple symmetric NACA airfoil made in two pieces, which snaps over the pole antenna? It could be retained/secured by the ball on the end but be free to swivel thus self-align with the airflow.
Gentlemen - Warm up your printers ... ;-)

Uli
'AS'