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  #1  
Old 05-18-2019, 11:15 AM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 604
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.

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  #2  
Old 05-18-2019, 01:18 PM
pa38112 pa38112 is offline
 
Join Date: Mar 2008
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, 10:20 PM
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Bugsy Bugsy is offline
 
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Location: Waukesha, Wisconsin
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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, 04:23 AM
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plehrke plehrke is offline
 
Join Date: Sep 2006
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 04:27 AM.
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  #5  
Old 05-19-2019, 04:54 AM
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Larry DeCamp Larry DeCamp is offline
 
Join Date: Apr 2010
Location: Clinton, Indiana
Posts: 806
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, 05:42 AM
mturnerb mturnerb is offline
 
Join Date: Apr 2015
Location: Ponte Vedra, FL
Posts: 951
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 05:47 AM.
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  #7  
Old 05-19-2019, 07:40 AM
mountainride mountainride is offline
 
Join Date: Jan 2018
Location: Golden, Colorado
Posts: 33
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 12:48 PM.
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  #8  
Old 05-19-2019, 07:41 AM
Red Mtn flyer Red Mtn flyer is offline
 
Join Date: Jul 2017
Location: Carson City, NV
Posts: 64
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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  #9  
Old 05-19-2019, 10:08 AM
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RV6_flyer RV6_flyer is offline
 
Join Date: Jan 2005
Location: NC25
Posts: 3,171
Default How about a different GPS antenna



How about using a different GPS antenna to save on installation work?

This GPS antenna works with the Stratus ES/ESG. I spent a little money using this GPS antenna to save installation work.
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  #10  
Old 05-19-2019, 11:14 AM
mturnerb mturnerb is offline
 
Join Date: Apr 2015
Location: Ponte Vedra, FL
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Default

Quote:
Originally Posted by Red Mtn flyer View Post
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.
I very much appreciate this commentary but find it hard to understand in the context of the discussion in this thread. What loads need to be transferred, and to where? Does the antenna itself create a significant load that needs to be transferred to structure? If the skin is clamped between antenna and a backing plate, where is the load going? Those of us who are not engineers may not really understand what you're trying to say.
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