[RVG8tor]

I have read AC-43 and they suggest a doubler tied into the aircraft structure for supporting antennas, or at least that is how I read it. To tie a doubler between floor ribs in the -8 this would entail riveting out already installed rivets to make a doubler to tie between the two floor ribs. Now for the most part drilling out a rivet is fairly easy but there are the few times if can become a mess. Do I really need to do this or would a doubler just riveted to the floor do the job just fine. My thought is a rectangle 2 inches larger than the area the antenna base takes up with two bends to form a stiffening flange.

I am not sure drilling out rivets in the floor ribs is a good idea. Thanks for any help. If you have done it the way I suggest and are flying please let me know how it has worked out and if you would do anything differently.

Cheers

 

[mannanj]

Doubler

I have read AC-43 and they suggest a doubler tied into the aircraft structure for supporting antennas, or at least that is how I read it. To tie a doubler between floor ribs in the -8 this would entail riveting out already installed rivets to make a doubler to tie between the two floor ribs. Now for the most part drilling out a rivet is fairly easy but there are the few times if can become a mess. Do I really need to do this or would a doubler just riveted to the floor do the job just fine. My thought is a rectangle 2 inches larger than the area the antenna base takes up with two bends to form a stiffening flange.

I am not sure drilling out rivets in the floor ribs is a good idea. Thanks for any help. If you have done it the way I suggest and are flying please let me know how it has worked out and if you would do anything differently.

Cheers

I don't have AC 43-13-2 in front of me right now but IIRC a doubler that is about 2 inches larger than the footprint of the antenna base should be about right. That should give you about 4x the area of the antenna base for support.

I think a doubler from stringer to stringer is overkill.

If you can dimple the skin and use flush rivets, that would be good, (that's the way I did it) but in the turbulent air under the front seat I don't think that would be necessary and that the AN 470 rivets on standard spacing would be ok.

 

[dmaib]

Here are a couple of shots of how I did mine. This does not meet the 2" size that Mannan mentioned, but too late now! I flush riveted a piece of angle along one edge of the double and then riveted the angle to the stringer and flush riveted the doubler plate to the bottom skin.

 

[Mike S]

A suggestion

You can also run a couple of diagonal braces from the two corner rivets farthest from the rib, a piece of 1/4" or 3/8" tube with flattened ends works well.

 

[jsharkey]

I Made a Channel Bridge Between the Seat Ribs on My -6

The doubler bridges between the seat ribs and is attached to the rib webs with one fixed and one adjustable angle flange and blind rivets. It has folded lateral edges for stiffness and sits flush on the belly skin. It is also used to mount nut plates for blind installation of the antenna. Apart from the antenna screws there are no other screws or rivets passing through the skin. It is one tough but light little bracket and there is barely any flex if you try and move the antenna - Clyde Built as they say where I grew up - as in ship building on the river Clyde in Scotland

Jim Sharkey
RV-6 Phase 1

 

[flion]

My thought is a rectangle 2 inches larger than the area the antenna base takes up with two bends to form a stiffening flange.

My COMM antenna is on top behind the baggage bulkhead and I used a full doubler especially because the skin is not as thick and there is less structure back there. My transponder antenna is also behind the baggage bulkhead but it is lighter and and the bottom skin is well supported so I used the method you suggest and it looks fine after the first annual condition inspection. I also used RTV adhesive (not sealant) to glue the doublers in before I riveted. If it were mine, I'd probably go with the doubler spanning seat ribs (we're not talking that many rivets and they're on the bottom of the aircraft) but I don't think I'd be worried if you choose to go with a doubler not tied into the structure. How's that for wishy-washy?

 

[RVG8tor]

My solution

Well after reading all the post I could find, it seems many do fine with just a doubler. I decided to not drill out floor rivets in my QB floor ribs. I sat down with the dimensions from the data sheet and made a template that I then used to drill two doublers. I still need to drill them to the floor, I discovered that the flange I added for strength interferes with getting the wing bots installed so I need to decide if I want the antennas further aft or if I want to radius the flanges where the bolts interfere or my last option is to move the antenna inboard. Moving the whips inboard would put them even closer together and moving them aft puts them closer to where I plan to put the transponder antenna so I am leaning toward making a radius in the flange to allow the bolt to clear. I am using a second doubler that is .025 and tear drop shaped, this will have plate but installed. I did not want to have to remove the doubler to replace the plate nuts that might fail at some point int he future. I plan to make a template for my CI-105 transponder antenna today. Thanks for all the inputs!

 

[JonJay]

My commant came with the doubler.

Right out of the box, standard part. I am surprised to see so many "do it yourself" approaches.

 

[apatti]

All,

Hasn't there been some issues with cracking around doubler plates that weren't secured to a rib? I know I have read about this with stiffener angles used on the bottom skin aft of the baggage compartment. So, I was concerned (perhaps overly so) about not tieing it to a rib. My doubler plate looks very similar to the ones pictured here. However, I did go ahead and tie it to one (not two) of the ribs. Similar to Jim's. Drilling out the rivets wasn't a big problem for me. I've gotten very good at that skill!!

 

[RVG8tor]

Same concern but

Tony,

I had the same concern and attaching into a rib is what AC43 recommends but I found some doubler designs that do not go to this extent, and on top of that there are many flying with just a flat plate as a doubler not even riveted into the bottom skin. I decided to go my route, I feel it is fairly robust approach and I don't risk messing up what is already riveted. My plan is to make this a focus area on pre-flights and annual inspections. I should catch any problems before they become a major issue. I can address a better design if it become necessary in the future. I applaud you drilling out the rivets, I find 90% are great but there is alway that one and wanting to get flying sooner and I am sure a bit of laziness I decided not to make repairs. Funny thing, Van's does not address antennas, if slow building I sure would add these doublers when building up the fuselage. QB you are kind of stuck reworking the area or going with a doubler riveted to the floor.

As to having problems I have not read more than one account of someone having cracks in the skin, and I did all kinds of searching looking for ideas. Of course I could have missed them.

Cheers

All,

Hasn't there been some issues with cracking around doubler plates that weren't secured to a rib? I know I have read about this with stiffener angles used on the bottom skin aft of the baggage compartment. So, I was concerned (perhaps overly so) about not tieing it to a rib. My doubler plate looks very similar to the ones pictured here. However, I did go ahead and tie it to one (not two) of the ribs. Similar to Jim's. Drilling out the rivets wasn't a big problem for me. I've gotten very good at that skill!!