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  #1  
Old 03-19-2023, 02:50 AM
Webb's Avatar
Webb Webb is offline
 
Join Date: Oct 2007
Location: Jackson, MS
Posts: 1,586
Default Under wing antenna location?

There are probably posts on this but I didnít see any so here goes.

Is there any reason a com antenna should not be mounted on the underside of a wing? Especially if there are 2 coms for separation distance.

Doesnít mean it doesnít happen but Iíve never seen it.

Hypothetically, letís say outboard the mains. Letís use a 4 or an 8 for the example airplane since the fuselage is narrower. That gives good separation unlike belly mounting.

There is access (inspection panel). Location for connector is dry. Low wing so pointy end of antenna is covered for those walking around donít get stuck.

It will cost a few more dollars for the extra coax but less radio interference from 2 coms would be the gain.

Why not mount under the wing?
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  #2  
Old 03-19-2023, 05:37 AM
swordtail swordtail is offline
 
Join Date: Oct 2011
Location: Grindstone, PA
Posts: 196
Default

Both of my vhf antennas are mounted on the bottom, between the landing gear legs on my 6A. It has worked for me, 1400 hours with no problem. They have a bend, not straight so they do not hit the ground. My ADSB antenna is on top.
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  #3  
Old 03-19-2023, 10:26 AM
FinnFlyer FinnFlyer is offline
 
Join Date: Aug 2018
Location: Bell, FL
Posts: 725
Default Drag?

Possibly slightly more drag. I understand that the air under the fuselage is already more turbulent than under the wing?
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  #4  
Old 03-19-2023, 01:55 PM
Avanza Avanza is offline
 
Join Date: Jul 2020
Location: Vastervik Sweden
Posts: 315
Smile 2 COM and 1 Antenna

Try this.

https://www.aircraftspruce.com/catal...?clickkey=9801

Good luck
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  #5  
Old 03-21-2023, 06:18 AM
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RV8RIVETER RV8RIVETER is offline
 
Join Date: Sep 2005
Location: 1T7, Kestrel Airpark , Texas
Posts: 790
Default Underwing

I have my primary comm antenna mounted under the wing. It is mounted to a re-inforced inspection plate, farthest outboard insp plate, right wing. I did this with the thought of being able to remove it for sport racing. No issues for 300+ hours.
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  #6  
Old 03-21-2023, 07:19 AM
John Tierney John Tierney is offline
 
Join Date: Jan 2006
Location: Vonore, TN
Posts: 636
Default

The image is from Stein Air FAQ webpage.
https://www.steinair.com/support/faq...-4598710e-6917

I only have a single comm antenna under the pilot seat, but if I needed a second would put it under the passenger seat. Contrary to Stein, put my ADSB antenna on the bottom behind the baggage bulkhead.
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  #7  
Old 03-21-2023, 05:25 PM
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czechsix czechsix is offline
 
Join Date: Mar 2006
Location: Spring Hill, KS
Posts: 425
Default

Quote:
Originally Posted by FinnFlyer View Post
Possibly slightly more drag. I understand that the air under the fuselage is already more turbulent than under the wing?
This might be true for a small transponder or ADS-B antenna (that an underwing location has more drag vs. on the belly) if your belly antenna is mounted directly aft of the cowl exit area where on most RV's the exit airflow is relatively slow (unless you're name is Dan Horton or Dave Anders, or you have a P-51). But for Com antennas which are quite a bit bigger, I've always assumed that getting the antenna out of the prop blast would reduce drag...in other words under the wing far enough outboard that the local airflow is slower, there should be less drag. Also anything in the swirling, turbulent air behind the prop may have separated airflow which increases drag vs. smooth airflow like you have outside of the prop blast. But I don't have any data to prove these assumptions...maybe there's a NACA report somewhere on antenna locations??

As far as antenna/radio performance goes, I installed my COM2 antenna about halfway out along the right wing on my RV-8A and it worked just fine there. What I didn't like about it in that location is it's easier for little kids at a pancake breakfast or fly-in to run under the wing and I worried about somebody poking their eye on it. If you put it under the wing, I recommend locating it a little inboard of the flap/aileron junction. Then if you park the airplane with the flaps down, it helps keep the kiddos from running under that part of the wing. If you have a sissy trigear model like me, don't put it too far inboard or it'll get in your way when you're trying to add air or change a tire on the main gear.
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