Wondering if one of you tube and fabric folks can help me out here:

I want to mount my GPS antenna on the top of the fuselage. Is it OK to bond an aluminum plate to the inside of the fabric and then screw the antenna down to that? If so, would one bond the plate to the fabric with fabric glue and cut a patch to cover it with similar to an inspection grommet or just bond the plate with (insert best adhesive here)?

Oh yeah, it's Superflight fabric system, their glue, etc.

Thanks in advance.

GB, are you mounting an antenna grounding plate further back on the fuselage for your radios? Could you mount your gps antenna to that same plate?

Thanks A1

The fuselage comes with a spot permanently fixed to the airframe to mount the VHF antenna.

Ok. On my citabria its just back and up from the battery. I had to extend my plating a bit to get better reception, and there is lots of room there to mount a gps antenna now. If one wanted to run the wire that far... luckily my aera gets great reception without an external antenna.
Wasn't sure how your plane was set up for the com antenna. Im sure someone here will have a better answer for you.
David

I mounted mine up under the Milloway glass instrument panel extension. Some others mounted theirs up under the greenhouse. Mounting to the top of the fabric without underlying fuselage structure could lead to problems as the antenna will flex and vibrate in the wind stream.

pouellette wrote:I mounted mine up under the Milloway glass instrument panel extension. Some others mounted theirs up under the greenhouse. Mounting to the top of the fabric without underlying fuselage structure could lead to problems as the antenna will flex and vibrate in the wind stream.

Hadn't thought of those alternate locations. Great idea. Thanks! Are your flying yours yet? I haven't made it all the way through your build blog. Lots of good stuff there.

Gb,

I'd definitely stay away from trying to mount an antenna to fabric. GPS antennas "see" just fine through plexiglass. On my 170, I mounted both the GPS and XM antennas front and center on top of the glare shield. They worked great there, no dropped signals in several hundred hours, and the bonus is, your cable runs are easy and short.

What type plane are you working on? Another possibility could be wing root fairing or fuel tank cover.

MTV

I mounted mine on the horizontal tube that runs across the top of the fuselage, just below the top/front of the windshield. I took a flat piece of sheet aluminum and wrapped it around the tube (think adel clamp) and mounted the GPS antenna on top of it. I've never had any issues with reception and I like that the antenna is inside, and not another 'drag' item in the slipstream. My radio antenna is also mounted inside so I have nothing protruding outside the fabric, other than those two 5 gallon tanks I just mounted on the struts. Oh, I guess those big a$$ Akbushwheels might cause a little drag also.

Gb- mount it on a plate under the boot cowl. That's fiberglass (unless your's is carbon) and will have great reception. If you have the vertical panel/glareshield option, you can mount it there as well. I tried to find a pic of mine, but can't locate one when the 696 antenna was mounted, but you get the idea.

MTV: its a Rans S7S kit we are putting together. It came as a quick build so pre - covered. Also hadn't thought of a wing root seal. Good idea too. Thanks.

WW: we are going internal with the 406 ELT antenna but never considered that on VHF. I sure like the idea. Obviously it works for you since it is there. Are you happy with the way it works? Thanks.

Emmitt: We have the carbon boot cowl. Any chance that would alter the reception from your experience with the fiberglass boot?

Thanks again all!

Generally GPS through carbon is a no-no, although I have not researched it thoroughly. If you haven't asked Rans, I'd call Ed or Randy direct. I just asked Randy on FB where they are putting them - if he responds, I'll forward.

Thanks.

I'm working on the various mounting tabs for my Bearhawk fuselage and have been thinking about the antenna mounts. Wondering what you guys recommend for antennas and methods for mounting on tube and fabric. Planing for a comm, nav, adsb, gps and elt antennas.

whee wrote:I'm working on the various mounting tabs for my Bearhawk fuselage and have been thinking about the antenna mounts. Wondering what you guys recommend for antennas and methods for mounting on tube and fabric. Planing for a comm, nav, adsb, gps and elt antennas.

IMHO, if you weld tabs to mount an aluminum "ground plane" plate onto the steel tube framework, make sure that the ground plane will be just under (inside) the fabric. You can mount the GPS and other antennae to this plate, making sure the antennae themselves are outside the fabric. MTV made a previous comment about not having the GPS antenna under the fabric and he's correct. Aircraft fabric covering/coating material has aluminum powder in it, which could possibly interfere or weaken signals trying to pass through it. Having an aluminum plate way down inside the fuselage is too much of a temptation to simply mount an antenna directly onto the plate.

So, again IMHO, mount the antenna so that the fabric is sandwiched and compressed between the antenna and the aluminum plate. Make sure that the mounting screw holes, BNC connectors, and ground wires are not insulated by the fabric... meaning that you have a good solid ground path between the steel tube airframe, the aluminum plate, and the antenna ground/mounting.

To do this without it looking ugly, you have to plan the tab locations in such a way so the aluminum plate will be flush, and not "above" or "below" the level of the fabric.

FWIW, my 96C handheld, mounted on my panel, has only lost signals once in 11 years--and that's with the signals having to get through aluminum and plexiglas on my P172D. That was at night when the satellites are at their lowest in the south, with the airplane going north. Also FWIW, I have my XM music antenna mounted under the back window, and it's always had a good signal. No ground plane is necessary for either GPS or XM. I don't think you'd ever notice enough deterioration of signals to write home about, if you mounted both types of antennas inside wherever it's convenient.

VHF antennas are something else, though. Those require a ground plane, and if it were mine, I'd want them well up above the tube frame. It doesn't take much to attenuate their signals--which is why the average handheld VHF with a rubber ducky antenna doesn't work very well inside any cabin, fabric or aluminum (I have a connection to my exterior com antennas for my handheld). You can hear fine, but transmission range is really short.

Cary

Personally, I would minimize/eliminate as many fabric penetrations as possible. GPS antennas work just fine on the glare shield and they are better protected there anyway. Comm antennas cam be mounted on the aluminum flashing between the wing and fuselage. My Nav antenna is located under the floor just above the stringers and does quite well there. The transponder is mounted on the bottom side of the boot cowl and is somewhat protected by the gear leg in that location. The only fabric penetration I made was for the ELT. But with 406, you don't even need to have an externally mounted antenna, so I wouldn't do that again, but that's just me. The less crap hanging off the exterior the better IMHO.

Is the glareshield metal? If so, just drill a hole through the glareshield for the cable, run the cable and protect it with a grommet, and mount the antenna on top of the glareshield. It's protected from the elements, and has a good view of the sky. My 170 had a Garmin 396 antenna mounted there, alongside the XM satellite weather antenna, mounted same way. Great location, never lost lock, and avoids external penetrations of any surfaces. Also easy to service if need be.

MTV

First off, this is the comm antenna we ended up with:

http://www.sirioantenna.com/index.php?m ... cts_id=228

Works like a champ, and cheap. Sorry to all you certified folks. [emoji24]

We tried an external mount comm antenna mounted inside the fuselage first. With a ground plane. Didn't work for shit. Very directional transmit and poor reception. This puppy mounted in a hole the factory left a bracket for on top of the fuselage with the intention of mounting ELT antenna there.

GPS antenna is mounted over the x brace above the cockpit. The signal penetrates the plexiglass skylight without issue.

No transponder yet, but it's set up for the antenna to mount on the bottom of the carbon fiber boot cowl with aluminum ground plane.

406 ELT antenna mounted inside the fuselage. Two reasons, 1: clean installation and 2: most wrecks I've seen end up with the airplane on its back and the antenna broke off.

No NAV antennas mounted.

I too want as few penetrations as possible. I forgot about the xponder antenna. I was thinking the comm would go where Blackrock said. The lower boot cowl by the gear leg sounds like a good place for the xponder antenna and maybe the ADSB antenna. Agree with keeping the ELT antenna inside. I'm planning for a 430w and don't know if there is a inside mount antenna that will work with it.

Sounds like I don't need to add any extra tabs for antenna mounts.

Hi Whee,

I am also building a fabric airplane and went down this same rabbit hole. Here is what I came up with.

I'm planning for a 430w and don't know if there is a inside mount antenna that will work with it.

The Garmin 400 series, W models are certified to TSO-C146a, which gives the lowest IFR approach minimums; great units. I have a 400W going into my build. To gain that certification the TSO (and other Garmin documents) have very detailed requirements for using the supplied antenna and mounting it exactly as detailed in the doc. The 400's require the matched antenna to gain the IFR capability.

There have been some complaints over the years of issues with these units, nearly all traceable to not following the antenna install specs to the letter (nearly all in the experimental camp as we don't have to pay$$ to have a shop install them). That and a few of the early antennas had bad pre-amplifiers that leaked moisture and failed due to over-tightening the mounting screws.

Long story short, either check with an approved avionics installer, or simply follow the mounting directions included, to a tee. The deal with those Garmins is they use an active GPS antenna (DC powered through the antenna cable from the unit) that amplifies the signal for large aircraft with long antenna cable runs. In our small aircraft the normal cable run is far too short, causing excessive signal gain to the front end of the GPS receiver resulting in all kinds of wacky, hard to troubleshoot failures to lock, loss of signal and general reliability issues no one can seem to fix.

My takeaway from all of it is to make sure the antenna cable is at least 15 feet or longer, wherever you put the antenna, and be sure to shut your eyes and pay for the recommended, exact part number of antenna cable, unless you have enough of a background in RF to choose the cheap cable with the exact specs. One avionics expert said it was OK to simply roll the cable up and stash it somewhere; that might work with the 100% shielding the antenna cable spec demands, but it makes me nervous as a former RF engineer. I suggest you carefully read the TSO, along with all Garmins docs, and decide for yourself.

Additionally IFR capable GPS receivers (TSO-146) continuously calculate solution accuracy, making it important the antenna has a perfect view of the sky, else once in a blue-moon the unit will show as degraded preventing an LPV (ILS equivalent) approach, or even a non-precision. Top of the cockpit seems like a good place in a front engine plane with non-direct cable routing to get the cable long enough.

Note VFR GPS receivers are not required to see as many satellites and therefore seem to work fine mounted on the dash. The rub with IFR GPS use is altitude is tough to get exactly right with GPS due to the physics of the system, meaning everything has to be spot on before you can depend on it on approach nearby the rocks.

I am building a pusher, so I have placed the antenna 3/4 out on the wing, just ahead of the spar, thereby improving the antenna's view of the sky and using up some antenna cable (my engine is on top of the back of the cockpit). Additionally the RF noise of the engine seems best to avoid, but there is little to no evidence that has ever been a reproducible issue.

Finally, as others have said, the Garmin antenna has all the ground plane it needs in the base. I simply put an aluminum plate (.030) between two rib bays, and fabric-ed over it with a large enough hole for the mount and built in o-ring, to seal. Be sure to torque and threadlock the screws exactly as directed.

-Jim