Drag of Transponder Antennae compared

Kenn Sebesta wrote on 2/10/2021 9:10 PM:
On Wednesday, February 10, 2021 at 5:47:39 PM UTC-5, Bob Hills wrote:
Thinking totally outside the box here and open to ridicule :).....

Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable.

Just a thought for someone to expound upon.

Bob 7U

I think you could do that, but there are a couple challenges

1. RF cable is heavy and significantly affects the signal. On sailboats, it's suspected that a stern-rail mounted VHF radio antenna actually performs better than a masthead mounted antenna. So sending it 5-10m to the wingtip instead of keeping it close to the TX unit could noticeably decrease range.
2. Even when in perfect shape, RF connectors are a big source of energy loss, which further reduces range.
3. The connector would have to be properly connected/disconnected every time the plane is pulled out of its trailer. A powerful RF transmitter which is disconnected from an antenna can actually destroy itself, so the consequences of a forgotten connection are not necessarily limited to only being invisible that day.

A better location would be in the fin, and I think some manufacturers offer that location. The
cable would shorter than going to a winglet (about 22' vs 30'); it could be even shorter (15')
if the transponder box (eg, a Trig unit) was mounted behind the gear instead in the instrument
panel. The fin could not be made of carbon, of course.

--
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