andy l wrote on 2/10/2021 4:30 AM:
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?
Remove the TE portion of the probe, and use electronic TE for the vario. Put the transponder
antenna in the fin. I've done the first part; not going to do the second part until I get a new
glider :^)
But what to do with the tip wheels? Got to be worse than a blade antenna. Take one off and taxi
only on the left wing? And that scoop on the sliding canopy window - better glue that shut
before I even think about using it again! Yikes - the yaw string - better mount it waaay back
on the canopy, behind your head, so it doesn't trip the laminar flow too early (or mount it
inside, towards the front, where I can still see it).
$200,000 for a new glider, and the manufacturer doesn't do any of these things! They must think
we are rich and bereft of technical knowledge. Also, why isn't there MK VII Laminar Flow Yaw
String I can buy? Did bumper retire?
--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1