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External Antenna Doubler

I

ingenieroe

Aerospace
Joined
Jul 17, 2025
Messages
2
I am designing an external doubler for an antenna in an unpressurized section of fuselage. I am struggling to find good resources on the matter. I am using AC43.13 as the main driver at the moment but I need more guidance.

At the moment I have the plate bonded to a single panel using a perimeter of rivets following edge distance, rivet pitch, and plate thickness as described by 43.13

I am considering having the doubler span more than one panel/bay because of grounding plane requirements and the single panel where the antenna could be is asymmetrical. However, from what I have read, this approach can increase the complexity of the design process due to the way the load is distributed. I'd like to know more about this.

What kind of testing/verification is required for a modification of this nature?

Any advice or pointers would be very helpful and appreciated.
 
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Which type of antenna is it? Is it a blade?
 
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Also, there are many other important considerations regarding antenna install to consider... not just structural.

Drag, interference, vibrations, aircraft dive speed, abuse loads [impacts, handling, etc], etc...

Clearance, electrical/electronic interference with other antennas and electrical equipment... wire/cable mounting/routing, etc

Static, lightning, bonding-grounding, weather sealing, corrosion protection, etc...

Size/mass/aero effect [flow] mounting on flat/curved surfaces... and adjacent substructure? Any significant structural deflections to deal with [localized, primary structure component].
 
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oh dear ... lots to consider.

as above, also damage tolerance (inspection of the fuselage skin under the doubler), repair of presumably existing rivet CSKs, ...

I don't think (but then not really my area) that the doubler needs to extend as the ground plane ... won't the fuselage skin do that ?
But maybe you need un-primed skin for the ground plane ? (then extending the dblr makes some sense)
Or maybe you need a different surface flat (normal to your antenna) rather than round ??

But first, who is approving this (for certification). Best get their buy-in early !
 
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what aircraft model?
part 23? 25? other?
approval by what regulatory agency?
 
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Apologies for the late response. I appreciate everyone's input, this is very helpful.

Part 23

What would an abuse load look like on an antenna?

When it comes to aero loading, is it better to use estimates that account for the entire "wetted" surface area of the antenna or only the "frontal area"?

As for the grounding plane, it is recommended to have quarter wavelength in radius of grounding plane. I wouldn't want to make the plane any larger than this and would prefer to make it smaller to avoid having it follow too much curvature of the fuselage. Does anyone have input on whether the grounding plane needs to be flat rather than being curved or if too many rivet holes will somehow interfere with the radiation pattern?

I have seen some doublers only use a perimeter of rivets but then I have also seen others have a pattern of rivets throughout the plane. Is there guidance on which is more appropriate?
 
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ok, pressuried fuselage or not ?

I normally abuse load at the tip, normal to the antenna (it is meant to "exercise" the fuselage attachment.

I would forget aero loads for anything except a large VHF (1" - 14") or a "toadstool/mushroom" antenna, with an endplate.
Any aero load is going to make a whole bunch of assumptions ... the critical load is lift due to sideslip.

Maybe no guidance but my typical practice is two rows around the perimeter and "field" rivets inside (maybe a 2" spacing ... maybe more, maybe less) and fay seal of course.
 
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