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  #1  
Old 05-18-2019, 12:15 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 621
Default GPS Antenna Doubler?

I'm installing my ADS-B GPS Antenna on the top of the fuselage in front of the vertical stabilizer. I'm questioning whether or not I need a doubler. The skin is very rigid back there and the antenna very flat. There's no leverage to generate a bending motion. I'd rather not put rivets in my nice paint job.

Michael-
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  #2  
Old 05-18-2019, 02:18 PM
pa38112 pa38112 is offline
 
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Location: Clarksboro, NJ
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Default

I made a backing plate that was roughly 1/3 larger than the antenna. I put rivet nuts on it and screwed the antenna into it such that it and the antenna sandwiched the skin.
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  #3  
Old 05-18-2019, 11:20 PM
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Bugsy Bugsy is offline
 
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Default Me to

I am switching my GPS from inside mount to on top in back same as you and also plan to use a piece of aluminum as a backing plate without riveting it to the skin. Kind of like a big washer held in place with lock nuts.
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  #4  
Old 05-19-2019, 05:23 AM
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plehrke plehrke is offline
 
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Location: Defiance, MO
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Default

Quote:
Originally Posted by Bugsy View Post
I am switching my GPS from inside mount to on top in back same as you and also plan to use a piece of aluminum as a backing plate without riveting it to the skin. Kind of like a big washer held in place with lock nuts.
Do you have a sliding canopy? If so, are You putting it on centerline behind slider track or off to one side and the canopy slides over the top of it?

To OP, I would use a doubler plate as skins are thin and any point mass attached locally will work on them with high potential of skin crack at the fasteners. Plus you potentially get a better ground plane for better antenna performance.
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Last edited by plehrke : 05-19-2019 at 05:27 AM.
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  #5  
Old 05-19-2019, 05:54 AM
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Larry DeCamp Larry DeCamp is online now
 
Join Date: Apr 2010
Location: Clinton, Indiana
Posts: 875
Default Glue

Glue the doubler on with 3m 2216 or equivalent. You will get some vibration damping in the process 👍
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  #6  
Old 05-19-2019, 06:42 AM
mturnerb mturnerb is offline
 
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Location: Ponte Vedra, FL
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Default

Quote:
Originally Posted by pa38112 View Post
I made a backing plate that was roughly 1/3 larger than the antenna. I put rivet nuts on it and screwed the antenna into it such that it and the antenna sandwiched the skin.
I did the same except used nutplates, and backing plate roughly same size as antenna (squared off corners and added space for nutplates) - see here: https://turnerb14a.blogspot.com/2018...-antennas.html

When I paint the airplane I'll bond antenna and doubler but for now just held in place with screws - torqued to Garmin specs of course.
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Last edited by mturnerb : 05-19-2019 at 06:47 AM.
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  #7  
Old 05-19-2019, 08:40 AM
mountainride mountainride is offline
 
Join Date: Jan 2018
Location: Golden, Colorado
Posts: 34
Default

I made my own. Garmin sells one for $50. I will rivet it in today. On the question of nutplates vs nuts, once I finally get my window installed the GPS will still be removable by one person.

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Last edited by mountainride : 05-19-2019 at 01:48 PM.
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  #8  
Old 05-19-2019, 04:44 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 621
Default

I haven’t drilled the holes in my skin yet. I started wondering if there were any structural issues with drilling a 9/16 inch hole in the skin of the tail cone. I ended up sending an email to Vans, but have’t heard yet.
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  #9  
Old 05-20-2019, 02:11 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 621
Default Vans Tech Support Response

Here's the response I received from Vans.

"We haven’t tested it but it seems unlikely that a small hole there would be a problem."

Not the definitive response I was hoping for. I guess I'll look for another place to mount the antenna. This is by far the most convenient place for my setup.

Michael-
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  #10  
Old 05-19-2019, 08:41 AM
Red Mtn flyer Red Mtn flyer is offline
 
Join Date: Jul 2017
Location: Carson City, NV
Posts: 85
Default i promised myself not to do this but

PLEASE go read 43.13. The nut plate method described does not transfer the loads, resulting in local stresses in the skin - which in your case is a STRUCTURAL MEMBER. The bonding method MAY be sufficient: how were the surfaces prepared? Was there a test model? Was that article tested to failure? Was the application methodology tested [temperature/ compression/ clamping]?
There are some metal to metal bonding methods that work, obviously, and have been for some time. BUT -- I have seen some otherwise great systems fail when used in the field.
Sorry, but this would not pass my inspection. Touch up paint is a lot cheaper than replacing a fuselage skin that cracks - or fails.
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