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  #1  
Old 06-05-2017, 10:34 PM
sritchie sritchie is offline
 
Join Date: Jun 2015
Location: Boulder, CO
Posts: 58
Default Guidelines on CI-122 wing doubler?

Hey all,

I'm currently designing my COM antenna placement around the motopod that'll be living on the belly of my RV10. Similar to this thread - http://www.vansairforce.com/communit...d.php?t=131359 - I've decided to put
  • 1 com antenna on bottom of the right wing (inboard)
  • 1 com antenna on top of the tailcone, just behind the first frame aft of the baggage bulkhead

What should I be thinking about for the doubler I'll need to install in the wing's bottom skin? Specifically, how much should I worry about tying the doubler for a CI-122 into the existing wing structure?

From easy to difficult, with the skins installed it would be
  • very easy to just add an aluminum doubler plate
  • a little harder, but not tough, to drill the rivets out of the wing spar and use that for structure
  • really damned hard to build a 90 degree angle from my doubler into one of the wing ribs

Will the first or second options be enough here? What are some good guidelines for building antenna doublers?

Thanks for helping me think through this one, folks.
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  #2  
Old 06-06-2017, 05:58 AM
Auburntsts's Avatar
Auburntsts Auburntsts is offline
 
Join Date: Jan 2005
Location: Dumfries, VA
Posts: 2,152
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Quote:
Originally Posted by sritchie View Post
Hey all,

I'm currently designing my COM antenna placement around the motopod that'll be living on the belly of my RV10. Similar to this thread - http://www.vansairforce.com/communit...d.php?t=131359 - I've decided to put
  • 1 com antenna on bottom of the right wing (inboard)
  • 1 com antenna on top of the tailcone, just behind the first frame aft of the baggage bulkhead

What should I be thinking about for the doubler I'll need to install in the wing's bottom skin? Specifically, how much should I worry about tying the doubler for a CI-122 into the existing wing structure?

From easy to difficult, with the skins installed it would be
  • very easy to just add an aluminum doubler plate
  • a little harder, but not tough, to drill the rivets out of the wing spar and use that for structure
  • really damned hard to build a 90 degree angle from my doubler into one of the wing ribs

Will the first or second options be enough here? What are some good guidelines for building antenna doublers?

Thanks for helping me think through this one, folks.
I have a Rami AV-17 in that location (first rib bay) and just used the doubler that came with the antenna following Rami's installation instructions. Since the ribs are close together at the root and there's not much skin flex I saw no need to tie the doubler to the wing structure. After 2 years of flying, no issues whatsoever.
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Last edited by Auburntsts : 06-06-2017 at 07:56 AM.
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  #3  
Old 06-06-2017, 06:03 AM
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rleffler rleffler is offline
 
Join Date: Jun 2006
Location: Delaware, OH (KDLZ)
Posts: 3,465
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If my memory serves me correct, there is a section in AC 43.13 that talks about antenna doublers. If you don't already have this, I highly recommend it for any builder to have available as a reference guide.

You can download a PDF from the FAA and there are several sources that sell hard copies.

https://www.faa.gov/regulations_poli...cumentID/74417
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  #4  
Old 06-06-2017, 07:50 AM
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majuro15 majuro15 is offline
 
Join Date: Feb 2013
Location: Charlotte, NC
Posts: 356
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I put a doubler in for the 122 under the belly and just tied it into one rib. I think if you tie it into one vertical and one horizontal plane, it should be just fine. Just my opinion, however.
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  #5  
Old 06-08-2017, 07:02 PM
WrightsRV7 WrightsRV7 is offline
 
Join Date: Aug 2015
Location: Hurricane Utah
Posts: 125
Default 43_13_2B good guidance...

Using 43.13.2B is always a good reference point, rarely the answer...it provides the drag formula so you can anticipate load...then you decide how to handle that...

D=0.000327 AV2 (The formula includes a 90 percent reduction factor for the streamline shape of the antenna.) D is the drag load on the antenna in lbs. A is the frontal area of the antenna in sq. ft. V is the VNE of the aircraft in mph.

Most com antennas give about 3 lbs of drag, not much. The FAA talks about doubler-plates most often for antennas and I think the advice by many above is very sound, having removed/replaced many many certified antennas over the years. In areas of thick skins, modest distances to structure (i.e. ribs, stiffeners, etc....) rarely have I seen doublers with rivet attachment, and very rarely with attachment to spars & ribs etc..... I often rivet the doubler, but that comes from having one less thing to move around when the antenna is serviced, not from a concern of structure. For what its worth. What a great process it is to build a plane!
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