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Transponder antenna under pilot seat?

T

tims88

Well Known Member
Would the spot in the picture work for a transponder antenna?

Thanks to a moment of extremely poor judgement while working on the plane tonight I have a very bad dent/hole right under the front left seat. I'm hoping I can just use this as the center punch for my transponder antenna hole rather than cutting it out and installing a patch. I'd have to position the coax between the brake and fuel lines but it looks like there could be room for that.

I'm pretty sure I've read other posts where people have said they installed an antenna under the seats but they probably had the luxury of planning out the location a little more precisely than I did.

PXL_20230620_023456091.jpg
 
Seems like it might work. My main concern is proximity/conflict with the fuel and brake lines going through those systems brackets. It does look like you might have dinged it almost exactly in between where the lines run.

Depending on whether you have a 3rd fuel return line might matter too.
The plans have the stock fuel line and brake line in the 2 forward positions and it looks like your ding is aft.
Adding a fuel return uses the 3rd position.

tims88 said:
Would the spot in the picture work for a transponder antenna?

Thanks to a moment of extremely poor judgement while working on the plane tonight I have a very bad dent/hole right under the front left seat. I'm hoping I can just use this as the center punch for my transponder antenna hole rather than cutting it out and installing a patch. I'd have to position the coax between the brake and fuel lines but it looks like there could be room for that.

I'm pretty sure I've read other posts where people have said they installed an antenna under the seats but they probably had the luxury of planning out the location a little more precisely than I did.

View attachment 44208
Click to expand...
 
I put my transponder and adsb antennae under the seats. Just be sure to read the instructions for displacement distances from other ant. I had to put them out very close to the outer edge of the floor to make the distance limits work.
 
tims88 said:
Would the spot in the picture work for a transponder antenna?

Thanks to a moment of extremely poor judgement while working on the plane tonight I have a very bad dent/hole right under the front left seat. I'm hoping I can just use this as the center punch for my transponder antenna hole rather than cutting it out and installing a patch. I'd have to position the coax between the brake and fuel lines but it looks like there could be room for that.

I'm pretty sure I've read other posts where people have said they installed an antenna under the seats but they probably had the luxury of planning out the location a little more precisely than I did.

View attachment 44208
Click to expand...

How bad, as in big, is the dent/hole compared to a rivet AN426AD4-x? It may be possible to clean up and properly dimple the hole and put in a "rivet to nowhere". I don't think it would need a patch. Then put the antenna in the best location for the antenna.
 
Mine is located in that same spot. You have a choice, you can mount your transponder antenna or your ADS-B receive antenna in that location. Same antenna....
 
AdamB said:
My main concern is proximity/conflict with the fuel and brake lines going through those systems brackets.
Click to expand...

I'm concerned about that too. I'm going to need a fuel return line so I'll be using all the slots. Hopefully there will be room for the coax to fit between them, or maybe a 90 degree connector would be able to keep it clear of the lines.

I have a CI-105 so I also have to see where the studs on the antenna would come through and make sure they won't interfere with the lines either.

lr172 said:
I put my transponder and adsb antennae under the seats. Just be sure to read the instructions for displacement distances from other ant.
Click to expand...

The hole for this would be about 35 inches from the mounting hole for one of my RAMI AV-17 antennas which is just short of Garmin's 3 foot minimum from other com antennas. Hopefully that's far enough to avoid any problems.

PaulvS said:
How bad, as in big, is the dent/hole compared to a rivet AN426AD4-x? It may be possible to clean up and properly dimple the hole and put in a "rivet to nowhere"..
Click to expand...

The main dent was actually caused by an 1/8" drill bit so it's just about the right size for an AD4 rivet. I really like this idea but I'm just not sure the depression that formed around the dent would be completely cleaned up by the dimple. I'll look more closely at this option before I drill a hole larger than a #30.

Pilot135pd said:
That would only happen if he makes a 2nd mistake and installs it on the inside of the plane. :D
Click to expand...

I wouldn't put it past myself at this point...

Bill.Peyton said:
Mine is located in that same spot.
Click to expand...

I'm glad to hear from others that this spot seems to work without much trouble. Other than it being just barely too close to a com antenna I've also wondered if being so close to the landing gear would cause any problems.
 
I mean

Its a ding on the belly of an airplane

Hold a bucking bar on the concave side and tap the pointy side.

And move on.

JMHO
 
I installed a Comant CI 105 under the pilot seat in my -10. Not an issue. Make sure of your flight controls, brake lines and fuel lines location first. So there will not be interference with the antenna installation. The Comant 105 does both transponder and ADSB so just one antenna for both.
 
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I decided to try to just hide the dent with a rivet or screw and ended up having to go up to a #8 screw to completely remove the dent/cracks in the skin. As you can see from the distortion in the photo, the dimple isn't the best but at least it's on the bottom.

I may still change my mind and try putting the antenna there at some point but it's just barely too close to the comm antenna that I put under the left rear seat. If I had the 3' minimum that Garmin's documentation calls for then I think this spot would have worked for me.

PXL_20230622_012032006.jpg

PXL_20230622_160556652.jpg
 
Both my comm antennas are located under the rear seats. Comm 1 is about 3 inch aft of the seat spar and about 5 inch inboard from the side. Comm 2 is the same under the right rear seat pan. The Comant CI 105 is under the pilot seat, slightly aft of the center point. 500 plus hours and zero issues with reception, including IMC flights. No static problems.
 
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