On Wednesday, 10 February 2021 at 04:51:35 UTC, AS wrote:
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'

One or two people with aerodynamics knowledge have said before that a delta is one of the highest drag shapes there is, if the airflow is not perfectly in line, and thus they personally won't have those fence fairings at aileron ends or flap end by wing root. Some blade transponder aerials look quite like a delta shape

How does the size and drag of a rod type transponder aerial compare with the short near verticle part of a total energy tube, and how often have people worried about that?

Simpler than the 3d printing would be take a short piece of curved mylar of suitable width, wrap it around and tape the edges together with capping tape. It might need a brief wave of a heat gun to enhance the curvature at the front (which is how it's curved in the first place).. It might take 3 or 4 tries or might not work. Don't do this for the TE tube.

Is there a prize for the first person to glue a nice mini Kamm-tailed fairing on the back of the ball, which doesn't fall off in the next few months? Am I joking?