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GPS Antenna Doubler?

Michael Burbidge

Well Known Member
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-
 
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.
 
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.
 
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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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/2018/11/engine-accessories-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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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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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.
 
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.
 
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.
 
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-
 
Just built my doubler today for the GPS antenna.

I have a tipup so placement is easier than slider. I put some floating locknuts on the doubler today will then use 3M silicone to adhere the doubler when I finish this up tomorrow.

The thing I’ve learned is that we have to be careful with doublers. We think by drilling the hole we are weakening the area so we go overboard with a doubler than ends up strengthening one area but ultimately creating greater stress around the doubler.
 
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