GPS antenna under cowling

I notice that several folks have installed their GPS antenna on a small shelf under the cowling, immediately forward of the firewall. I am considering doing the same thing. Anyone who has done this, can you tell me 1) that it still does receive ok and 2) are there any issues with heat?

thanks,

greg

Greg Arehart said:

I notice that several folks have installed their GPS antenna on a small shelf under the cowling, immediately forward of the firewall. I am considering doing the same thing. Anyone who has done this, can you tell me 1) that it still does receive ok and 2) are there any issues with heat?

thanks,

greg

Click to expand...

1. Yes

2. No

I will work just fine. But, be aware there might be interference with the right side firewall/upper cowl hinge pin insertion/removal.

Instant gratification

Talk about a quick turnaround! Thanks for the info. Great to have this stuff answered almost instantaneously.

cheers,
greg

I would expect that installing the antenna beneath the cowling would decrease the received signal strength. My 295 will lock up on a heavy overcast day. Adding a sheet of metal will between the antenna and the sky will quicken the onset of lockup.

Cessnadon,

Cowling is made of fiber glass and not metal. Depending on how close it is to the cowling, it may have better view to the sky than an antenna on top of the glareshield (partially blocked by rollbar, etc)..

For some reason, my antennae didn't want to work over the instrument panel, so the glareshield was out. Since they both came with long leads which I was told not to cut in the manuals, I decided to put them in the wingtip. My friend who built a Lancair propjet had his in the tail cone under fiberglass (just glass, no carbon or anything else, failed to get it to work and ended up having to put his external. Because of that, I towed my project out of the hangar and fired up the panel with the antennae on the wing. 8 sats (the hangar blocks the view south). Then I moved them under the wingtip and watched the display. Still 8 (occasionally 9 or 7). While I am not aware of anyone having problems with the heat under the cowl, I decided not to take the risk anyway. Also, it was easy suspending them under the wingtip; I just made a little 'shelf' from .040 sheet that rests 1/2" below the top surface and rivets to the top. A little velcro to stick them down and it was done.

I too, plan on putting my 430w antenna under the cowl...BUT, I still am concerned in that as I understand the situation, I'm required to follow the install manual to end up with an approved IFR GPS installation. AND, under-the-cowl antenna installations are not shown in the manual. Instead, fairly specific locations are specified...

Anyone have any definitive info on this?

I put three under the cowl

The antenna for the 430 and one each for my two BMA EFIS units.
I build a small shelf to hold them close to the top of the cowl and forward a little. All get good reception and have had no problems to date.

The only downside is the restricted access when changing the oil. I did mount it with platenuts and screws so that I could remove it if needed.

See top of picture.



Kent

1. Yes
2. No

You WILL have signal reduction on metallic paints. Pearls(small flake) are negligable(sp?). But even the big flakes work albeit under reduced signal strength.

Works ok

Hi Greg,

Make sure the antenna "sees" as much as possible (something like a 2x45 degree cone from the center of the antenna), then it works fine. I heve a picture on http://websites.expercraft.com/PHVII/index.php?q=log_entry&log_id=14708

FWIW

My 430W antenna is on top of the glaresheild..works great.

Frank

The WAAS antennas are much more needy when it comes to "seeing" the sky...whereas the old non-WAAS antennas would work about anywhere, the likelyhoold of the WAAS antennas working really well for a long period of time while being placed under the cowl isn't good.

The Glareshield is ok for WAAS antennas, but not very good....as you need quite a bit of cable between it and the unit (at least 8') to have acceptable integrity of the WAAS system. If you stick the antenna really close to the 430/530W and don't make the cable long enough, it just won't work. If you make the cable long enough, now you just have a bunch of coax wound up under your panel, which also isn't the greatest. We've had a LOT of customers having GPS issues when upgrading their units to WAAS, and that's almost always the issue. So, we recommend placing it outside (I know, costs .5kts), but at least it'll work properly with no shadowing in any direction.

My 2 cents as usual!

Cheers,
Stein

Under cowl is fine

I have my 430 antenna along with my 496 and XM antennas mounted on a shelf under the cowl. They work great there.

Regarding the heat, I spoke with Garmin and got the "unofficial," word that this is a good place. The heat really isn't the issue. The guy told me the sun is a bigger killer.

Also, very few metallic paints use true metal flakes anymore. Many are plastic flakes that won't have any affect on reception.

RV7Guy said:

I have my 430 antenna along with my 496 and XM antennas mounted on a shelf under the cowl. They work great there.

Regarding the heat, I spoke with Garmin and got the "unofficial," word that this is a good place. The heat really isn't the issue.......

Click to expand...

The under cowl mounted Garmin 430 GPS antenna in my -6A has for three years now, performed well. I also have a sill mounted 296 fitted to "Darla!" and have found that 100% of the time, satellite acquision is faster on the 430 than the Garmin 296 unit fitted with its duck antenna.

Before I undertook the firewall mounted antenna installation, I too contacted Garmin and was verbally assured...for what that is worth....heat is not an issue. I cannot comment on other GPS's. It is probably best to check with GPS manufacturer first.

Rick6a said:

The under cowl mounted Garmin 430 GPS antenna in my -6A has for three years now, performed well. I also have a sill mounted 296 fitted to "Darla!" and have found that 100% of the time, satellite acquision is faster on the 430 than the Garmin 296 unit fitted with its duck antenna.

Click to expand...

FWIW, my Garmin 496 is much, much faster than my 296 for satellite acquision, even when the antennas are in the same area. So possibly it's just the units???

L.Adamson