Antenna location

[Arrow76R]

Query...for in-flight ops is it better to have the com antenna mounted on the bottom or top of the fuselage? Seems like the bottom would have more "view" of the ground-based sites. Conversely, for ground ops (i.e. clearance delivery, ground, local control) seems like an antenna on the top of the fuselage would be better....Thoughts???

 

[biplanebob]

If you have 2 comm radios, why not antennas in both locations. The Piper Cherokees that I flew in the 1970's for PVT, Commercial, and instrument all had the antennas on top.

 

[geezer]

Antenna's on the bottom get physically abused, and their insulators gradually short out as dirty oil coats them. On the bottom is more efficient otherwise.

Transponder and other very high frequency antennas are normally on the bottom, and we regularly clean the insulators on our transponder or the signal gets weak and the FCC/FAA get after us. Enforcement in the Washington DC areas has rising and falling enforcement surges.

Carbonized oil even deteriorated our ADF radio sensitivity if we went too long between plane washes.

Tied down on grass, the lawn mowers would be quite a risk for any antenna that was both long, and on the bottom.

 

[Arrow76R]

My Arrow has the broadband VHF antenna (com 1) on the top and a "bent wire" antenna (com 2) on the bottom. I was thinking of swapping the bent wire for another broadband and switching the com 1 radio to the bottom antenna and, of course, comm 2 to the top. Only because of the "view" from the two locations. Yes, my transponder antenna and one of the 2 diversity ADS-B antennae are on the bottom along with the marker beacon antenna. I do clean all the bottom antennae from time to time. Yes, I have also seen two comm broadband antennae on the top. On my previous plane, Skyhawk, both com antennae were on the top which is where I see most Cessna comm antennae mounted.

 

[weirdjim]

My Arrow has the broadband VHF antenna (com 1) on the top and a "bent wire" antenna (com 2) on the bottom.

The reason for the "bent" wire is in a real belly-whomper the straight antenna has every chance of contacting the ground. If you are LUCKY it will destroy the antenna. If not lucky, it will peel back skin where the antenna is attached to the fuselage. For the oil problem, a very simple and low-drag solution is a small curved aluminum (or plastic, for you 3-d printer folk) slipstream deflector in front of the antenna solves that problem. You only have to protect the insulator, not the whole antenna. (carbon on aluminum is still a conductor).
Jim

 

[chemgeek]

Bottom works better in the air, top works better on the ground.

 

[Plano Pilot]

Bottom works better in the air, top works better on the ground.

Our Citation has the #1 comm on the tail and the #2 comm on the belly. It works best to use the #1 on the ground and the #2 in the air. At our home base there is a concrete wall where we normally depart. Ground/clearance has a hard time receiving us on #2.

 

[kshaw]

My avionics shop recommended one on top and one on the bottom. I do not see much difference between the two, though.

 

[Arrow76R]

Thanks all for the inputs. Seems logical that the bottom one would work better in the air "looking" down while the top would work better on the ground "looking" horizontally or up since most control towers have their antennas on the roof. I will be having an upgrade to my autopilot in a few weeks and will ask the avionics shop about this.