What's new
Van's Air Force

The definitive Van's Aircraft support community! Buying, building or flying an RV? Join our exclusive family of mentors and enthusiasts!

Showplanes Fastback antenna placement

L

lonkelm

Active Member
Before I dive into section 32 the big join, I want to as much wiring and determine antenna placement.

I want to do one up top an done on the bottom for Coms. For anyone with the fiberglass fastback from showplaces, did anyone put an antenna up top? was it outside or under the fiberglass?
 
You're about where I am! I also have the composite tailcone and am considering antenna locations top and bottom, rather than the usual locations under the rear seat bays.

I haven't placed the antennas yet, however I have a RAMI AV-17 and RAMI AVT-4. The plan is to put the AVT-4 up on top of the composite tailcone with the requisite ground plane, and the AV-17 on the bottom of the airplane, centerline, at the far aft of the box formed by the battery/elevator bellcrank deck and bellcrank ribs. This is well out of the way of the bell crank, but is the only place on the fuse where the centerline of the aircraft is not blocked by a stringer or where the elevator push/pull tube runs close to the skin. The plane is to terminate the RG-400 to a right angle BNC so that the wiring immediately escapes the box area to the left or right. I wish I could provide a pirep on how this arrangement worked out, but this is at least our plan, and perhaps someone else on VAF can nitpick it.
 
lonkelm said:
Before I dive into section 32 the big join, I want to as much wiring and determine antenna placement.

I want to do one up top an done on the bottom for Coms. For anyone with the fiberglass fastback from showplaces, did anyone put an antenna up top? was it outside or under the fiberglass?
Click to expand...
Have the fiberglass fastback from SP and installed a Starlink under the skin, works well. Comm antennas under the front seats.
 
Walt said:
The AV-529 has much lower VSWR with smaller footprint.
Click to expand...
If you're comparing to the AVT-4, you are of course correct, though the drag figure is almost 75% less. The bent whips from RAMI and Comant have the same 3.0:1 VSWR, so it's not like it's unusually bad.

I'm mounting the AVT-4 on top of the cabin, vs two bent whips under the seats, so even with the somewhat poor VSWR of this antenna, I'm guessing my COM performance will still be better than the under belly configuration. Especially so since both of those bent whips would otherwise have the same VSWR and be mounted less ideally.
 
Have you seen the AVT-4 in person? I believe it larger than you might think.
I have a 529 belly mounted in the fwd/center fuselage area and a bent whip for com 2 towards the rear.
(I previously had a comant antenna on the top but didn't really like the looks of it)
I prefer to eke out every bit of performance possible from an antenna with lower VSWR.
 
chris1seto said:
You're about where I am! I also have the composite tailcone and am considering antenna locations top and bottom, rather than the usual locations under the rear seat bays.

I haven't placed the antennas yet, however I have a RAMI AV-17 and RAMI AVT-4. The plan is to put the AVT-4 up on top of the composite tailcone with the requisite ground plane, and the AV-17 on the bottom of the airplane, centerline, at the far aft of the box formed by the battery/elevator bellcrank deck and bellcrank ribs. This is well out of the way of the bell crank, but is the only place on the fuse where the centerline of the aircraft is not blocked by a stringer or where the elevator push/pull tube runs close to the skin. The plane is to terminate the RG-400 to a right angle BNC so that the wiring immediately escapes the box area to the left or right. I wish I could provide a pirep on how this arrangement worked out, but this is at least our plan, and perhaps someone else on VAF can nitpick it.
Click to expand...
Cool/ interesting. So you see it going behind the cabon on the composite tailcone. Where will your GMU22 go? by baggage bulkhead / standard location? Will it be too close? It's on eof the questions I"m pondering vs two bent whips under.
 
Walt said:
Have you seen the AVT-4 in person? I believe it larger than you might think.
I have a 529 belly mounted in the fwd/center fuselage area and a bent whip for com 2 towards the rear.
(I previously had a comant antenna on the top but didn't really like the looks of it)
I prefer to eke out every bit of performance possible from an antenna with lower VSWR.
Click to expand...
Is the 529 behind the spar or ahead? Is there suffient clearance with the almost 22" straight 520? Roughly what bulkhead is the bent whip?
 
Walt said:
Have you seen the AVT-4 in person? I believe it larger than you might think.
I have a 529 belly mounted in the fwd/center fuselage area and a bent whip for com 2 towards the rear.
(I previously had a comant antenna on the top but didn't really like the looks of it)
I prefer to eke out every bit of performance possible from an antenna with lower VSWR.
Click to expand...
Yeah I already bought it. It is larger, but the drag figure is still smaller. The cylindrical profile of the 529 in the slipstream is brutal for aero..

....That said, I do realize that I'm talking about tiny figures in the grand scheme of things. That .0125kt is worth it, of course.

My philosophy has basically been to avoid doing anything on the build which is worse than typical, and most RV10s have the dual belly mounted antennas (which aren't even a known problem point except for with older generation radios which sometimes have interference issues). Given both of the belly mounted antennas will have the same VSWR and are mounted in a less advantageously than one antenna on top and one on bottom, I'm at least likely doing better than typical.



lonkelm said:
Cool/ interesting. So you see it going behind the cabon on the composite tailcone. Where will your GMU22 go? by baggage bulkhead / standard location? Will it be too close? It's on eof the questions I"m pondering vs two bent whips under.
Click to expand...
We're putting our GMU11 in the right wing tip
 
chris1seto said:
Yeah I already bought it. It is larger, but the drag figure is still smaller. The cylindrical profile of the 529 in the slipstream is brutal for aero..

....That said, I do realize that I'm talking about tiny figures in the grand scheme of things. That .0125kt is worth it, of course.

My philosophy has basically been to avoid doing anything on the build which is worse than typical, and most RV10s have the dual belly mounted antennas (which aren't even a known problem point except for with older generation radios which sometimes have interference issues). Given both of the belly mounted antennas will have the same VSWR and are mounted in a less advantageously than one antenna on top and one on bottom, I'm at least likely doing better than typical.




We're putting our GMU11 in the right wing tip
Click to expand...
Hmm, CANBUS going to be long enough? That's typically the wing with the autopilot servo so would there be interference concerns?
 
dmattmul said:
Why? Put it in the upper section of the fiberglass tailcone. Zero interference. Lots of amp draw users in the wing to throw it off.
Click to expand...
hmm, GMU11 in tailcone hadn't thought of that. Was thinking of wing tips vs rear bagagge bulkhead (standard location). Wings I worry about interference. Heated pitot on left, autopilot servo on right plus landing lights (seven stars).
 
dmattmul said:
Why? Put it in the upper section of the fiberglass tailcone. Zero interference. Lots of amp draw users in the wing to throw it off.View attachment 104301
Click to expand...
In hindsight, I wish we had, but the wiring harnesses were already made with the idea of locating it in the wing. I think it'll likely be fine, though you're right that the tailcone would be a more convenient place to put it. That mount you made looks very similar to the one we made for the GPS antenna.

lonkelm said:
Hmm, CANBUS going to be long enough? That's typically the wing with the autopilot servo so would there be interference concerns?
Click to expand...
Apparently it's short enough. Aerotronics did the harness, so I assume adhering to the length restriction is part of their process.
 
You must log in or register to reply here.
Back
Top