The Barn Find Build

[109JB]

Mine has not had operational tests as it is in the covering stage of the rebuild. I don't have to worry about airworthiness because my airplane already has one since it is a rebuild project. Before I got it there was a AmeriKing AK450 ELT in it and I opted for the Artek ELT 345. I have read reports that they work fine inside the fuselage. I figure it will be better than the iffy AK450. Will be testing when its warmer though.

[Eric Page]

I started today's efforts by finishing the physical installation of the autopilot pitch servo.

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I'd appreciate it if someone who's done it a few thousand times could critique my safety wiring. To my eye they look pretty close to the drawing in AC 43.13, but I'm biased!

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I also sanded down the SuperFil that I applied a few days ago in the extra slots that the first builder made in the rudder's fiberglass fairing.

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Next I spent a ridiculous amount of time fabricating two small aluminum plates to serve as ground planes for the transponder and ADS-B antennas. I don't know why this was such a trial, but every time I touched something it went wrong. I should have downed tools and gone inside for awhile, but I'm stubborn. They ended up the way I wanted them, but not before I told a few of my tools what I thought of their maternal line.

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Finally, I started working on a way to mount them in the wings. This will involve some small spacer blocks that I fabricated out of a 3/8" square pine dowel.

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Those will lower the base of the antenna a bit from the top of the wing, leaving room for a right-angle BNC connector. More on that later.

[jrevens]

Eric... regarding the safety wire - since you asked, it's close, but not exactly how I would do it. I think you should have started the final twisting of the pigtails right where the wire exits the hole in the head of the bolt.

[109JB]

Your ground planes look too small to me. The transponder ground plane should be a minimum of 5.5" and if using a minimum size ground plane they should be round. The ADS-B would be about the same. The rule of thumb is the ground plane should have a radius of 1/4 wavelength. The transponder is 1090MHz

Wavelength = (Speed of light)/frequency = 299,792,458 / 1,090,000,000 = 0.275 meters

Radius = 0.275 / 4 = 0.06875 meters =68.75 mm = 2.71 inches ---> so 5.42 inch diameter

[PapuaPilot]

I will give you my honest opinion. As a maintenance instructor I would have you do it again.

1. Notice in the picture in AC43.13-1B the twisting between the bolts goes all the way from bolt head to bolt head.
2. The finishing or next twist starts where it comes out the opposite side of the bolt head.
3. Lastly the wire needs to be twisted in the opposite direction where it comes out of the head so that the outside wire stays against the head.


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My antenna ground planes are round and about 6" diameter.

I have never seen transponder antennas mounted on the wing. There is a reason they are mounted on the bottom of the fuselage so they have a full 360 degree downward view. The signal may get blocked by the fuselage if they are mounted too far inboard on the wings.

[Eric Page]

I think you should have started the final twisting of the pigtails right where the wire exits the hole in the head of the bolt.

Ah, OK, I see what you mean. I'll give it another try tomorrow and see if I can do that. Thank you!

Your ground planes look too small to me.

Well, that's embarrassing. I'm glad you can't hear me right now. Would you believe that I had an exchange about this on another forum yesterday, in which I mistakenly wrote "diameter" when I meant "radius?" I knew all along that the number I came up with was a radius but I not only wrote it wrong, I actually made them wrong, despite being corrected by two people on the other forum!

Would you also believe that the piece of material I used to make them is now too small to get two parts of the correct size?

GRRRR!!!

[PapuaPilot]

AC43.13-2B in Chapter 3 is the place to look for information on mounting antennas and ground planes. It's a fairly short read, but packed with information. They don't forbid transponder antennas on the wing, but it isn't best practice.

[Eric Page]

I will give you my honest opinion. As a maintenance instructor I would have you do it again.

1. Notice in the picture in AC43.13-1B the twisting between the bolts goes all the way from bolt head to bolt head.
2. The finishing or next twist starts where it comes out the opposite side of the bolt head.
3. Lastly the wire needs to be twisted in the opposite direction where it comes out of the head so that the outside wire stays against the head.

Thank you. I missed a couple of the fine details in that diagram. I'll give it another try.

My antenna ground planes are round and about 6" diameter.

I have never seen transponder antennas mounted on the wing. There is a reason they are mounted on the bottom of the fuselage so they have a full 360 degree downward view. The signal may get blocked by the fuselage if they are mounted too far inboard on the wings.

Yeah, I screwed up the size. No surprise after the day I had in the garage. I'll start them over.

I plan to put them fairly far outboard.

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Now I'm fed up to my eyeballs with today, and I'm going to bed.

[PapuaPilot]

Here is how I did my transponder and ADSB antennas. One is behind the pilot on an existing mount and I added the ground plane. The other is just aft of the copilot stick and I mounted it using 2 adel clamps to the bracket and ground plane. After I took the picture I added a wire to ground it to the airframe.

They are almost 3' apart and have worked flawlessly for 5 years.

It seems like your plan to put them in the wings is adding unnecessary complexity and weight.

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[Eric Page]

You know, Phil, this whole thing would be a lot easier if you'd just sell me your plane. Then I wouldn't have to copy everything you did.