ELT Mounting PA-18 - ME406

Time to replace the beat up old ELT and get a 406 installed. Looking for any guidance on installation locations for the ELT and antenna. The old ELT was installed behind the back seat under the window on the left with the antenna inside. Thinking about using the same spot and putting the antenna outside above the wing root.

Any thoughts appreciated.

Mike

Go with an ELT that allows mounting the antenna within the fuselage. I'm using the Kannad 406... the electronics shop mounted the antenna at the wing root opposite of the comm antenna...the distance between the antennas was to close according the Kannad's installation instruction manual. During rebuild I fabricated an antenna mount between the wing and vertical stabilizer, the mount was a modification to the stringer stand off...added copper foil to an extra layer of fabric...under the external fabric to create a ground field.....the antenna location was per Kannad. So....if I wind up...upside down....less likely to knock off the antenna. Kannad would not permit mounting of the antenna within the fuselage.


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I was able to get an ACK 04 approved with the antenna mounted on top of the extended baggage, slanted to fit within the fuselage.


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Steve, you mean inside the fabric? I don't have any access in there unless I pulled that out. I've also been told that the antenna really needs to be outside. AC 41.13 wants 36 inches between antennas which means I'd have to put the ELT antenna up front on the wing root on the other side which is probably OK just won't look symmetrical.

Where did you mount the ELT?

The ELT is mounted on the battery shelf over the extended baggage compartment. I'll try to get a picture of the antenna installation tomorrow. IIRC, Huskies mount the antenna inside.


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Pay attention to the installation requirement for mounting to structure. No more then 1/10th of an inch movement with 100# of pull in the most flexible direction. That's the hard part. My new ELT antenna is mounted on the fuse top ahead of the fin. That's the most logical place in my opinion. I haven't seen any evidence that internal installation is an advantage or external mounting is problematic. Evidence that the ELT mount wasn't adequate and the coax being ripped out when the mount failed can be found.

ME406? I've had a couple and when those were installed they couldn't be GPS enabled. Has that changed?

What kind of plane Stewart? I'm all fabric back there.

Cub, but it's a build project so the opportunity was there. If your 121.5 antenna mount is good why not stick with it for the new antenna?

Considering that but just wanted to see what others have been doing. Thanks.

Anyone noticed any issues if the antennas are inside of 36"? I'm thinking my Wagon's two com antennas are closer than that.

sjohnson said:

The ELT is mounted on the battery shelf over the extended baggage compartment. I'll try to get a picture of the antenna installation tomorrow. IIRC, Huskies mount the antenna inside.

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Which means you have the battery door on the back? Not us. Battery is up front.

FWIW, my old -12 had the ELT antenna aft on the right wing root and the comm antenna forward on the left wing root. Lots of Cubs are set up that way. The only reason my new one is moved aft is to get it some protection from the fin should it go on its back. That said I haven't seen any reports of a wing root antenna failing to broadcast when the plane was on its back. We know they work from inside closed hangars. I can't find a link but I recall the Artex chief exec commenting that 406s work fine with no antenna. If that's true it would be better yet in a tube and fabric airplane.

Not ideal but should meet the deflection requirements. Not a lot of good locations to mount this on a sealed up cub. I haven't committed yet so don't be afraid to raise the flag.

Am I smoking hopium or would this be legal?

Re the latter: nope.

And quit smoking that stuff.....

Skywagon185 said:

Am I smoking hopium or would this be legal?

View attachment 30828

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What you put in your pipe and smoke, is your business...

But. That antenna is designed to operate from a vertical position. Straight up or straight down. So the best broadcast from this install is off one wing tip or the other. Unless you end up on your nose. Also the ground plane at the base of the antenna is not good. Ground plane is a conductive surface not simply a ground connection. If you place an antenna on a small ground plane (as opposed to, say, a Cessna metal wing) it needs to be placed at or as near the center as possible. If you mount the antenna at a corner like this it will broadcast mainly in one direction (in this case, away from that corner).

Web

Skywagon. Mounting on the plywood panel will be no problem as long as the panel is properly attached and meets the deflection criteria. See Stewart's post at #6.

I, too, suspect bad mounting in several recent crashes where the 406 ELT did not actuate. I believe it is because these units use accelerometers instead of a simple G switch. A G switch will trip any time it's exposed to an impact or sudden stop that exceeds it's preset limit. An accelerometer will measure the acceleration or deceleration of the unit it's attached to. My opinion is that the flex in the mount 'softens' the deceleration felt by the unit upon a crash and sees it as less than it's designed trigger threshold. You engineer types can chime in any time here.

And don't mount an antenna inside a ferrous metal cage (fuselage tubing) and cover it with metallic panels (silver dope on your fabric). Even if you can make it work some how, you are decreasing the signal strength on a piece of gear made to help people find you. Not a good idea.

Web

The AKC and Airtex ME406 allows mounting of the antenna within a composite and tube and fabric aircraft.....the non-conductive issue maybe the aluminum coat of polyfiber..... wonder what is in Stewart's system echo prime? I went with Superflight system 7.... don't believe there is anything in the paint is considered a conductive coating in either the fabric primer or top coat?...with that said...was required to mount my Kannad antenna externally.


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Another way to look at it is that it is a quarter wave antenna that you pull out of the box, BUT there is no such thing as a quarter wave antenna. There are only, as a minimum, half wave antennas.
Therefore, it is up to you to turn it into a half wave antenna by adding the other quarter wave portion. You do that by mounting it to a ground plane . The ground plane does not have to be of a resonant radius because there only has to be one resonant element in your antenna , preferably the one you are feeding so that you can impedance match the feed to the antenna by using it as a matching transformer....the RF current, and therefore the magnetic portion of the electro-magnetic signal, is maximum right where the two elements join, so you need to make sure it's a good connection.
In order to radiate, the resonant part needs to be CLEAR of all other conductive structure, otherwise, everything within several wavelengths becomes part of your antenna circuit. A very lossy part. It de-tunes the antenna, causing power to be reflected back to the transmitter, heating it up. All of the steel near your antenna conducts part of the signal and due to the fact that it IS NOT copper, turns it into heat. Worse yet, it tends to act as parasitic elements, reflecting power in many weird directions, and NOT in the direction you want. The radiating element, the one you pulled out of the box, has to be CLEAR of surrounding metal structure, in line-of-sight to the satellite. If you mount it inside, the structure directs the signal in whatever direction it wants, and if the fuse is covered in metal-doped fabric, one TENTH of your power will make it through, just from the fabric attenuating it.
The path loss fade margin to the sat is approximately 35 db , so if you want to use it up doing stupid stuff, then go ahead. It's there as a safety margin. Treat it with respect.

Sheesh, I thought this was going to be short....and simple...

Just read #6 and #19.

The rest of us are in the crowd holding up lighters . . . .

Web

The issue that keeps bringing this subject back up, is the fear of breaking off the antenna in a flip-over.
If you mount the antenna in the ideal place, on top of structure, it is extremely vulnerable to breakage. The most ideal place for survivability, in my opinion, is back towards the vertical stab, but mounting is problematic. When I discussed solutions a few years back with a bud who had new fabric on his cub, his face turned pale and I thought he was going to tip over when I mentioned that he would have to cut a big hole in his fabric, so I understand the reluctance. Happily for me, though, MY fuselage fabric is old Ceconite with many, many patches, so major surgery is something that isn't too ugly a thought. Your mileage may differ. Here's another thought, though. Mount it upside down on the wing halfway between the strut attach and the fuselage. You might put an eye out, but it would be better than on top, as far as vulnerability. If you do decide to mount it on top back by the tail, here's a bit of what I had to do.


Taped down coax was three layers of friction tape around tube, then the coax, then four more layers, with a black tie-wrap around outside. Don't forget chafe tape between fabric and adel clamps...like I did....fabric patching was Stuart's....Red box on the right of second picture was Shark ELT, since removed. Note the ELT mounting platform. A .025 2024-T3 and 1/4 in plywood sandwich, with a built-in I beam for rigidity. (riveted together with 1/8 rivets and glued) Deflected .04 in with 100lbs at the I beam, so less at where the ELT mounts.

Update, now complete. It's solid.







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How did you mount that hydraulic pump?

Little late for this, but years ago I used to make up roll up antennas out of TV twin lead, in the ham radio " j pole" style, with a BNC connector and cut for 121.5.mhz.
Many times when you wreck a cub the ELT antenna is
broken off. So you simply unhooked the broken coax, that
was hooked to damaged antenna. Unrolled the twin lead J
Pole and hooked it to the ELT and BINGO you were now transmitting on 121.5.
Lots of bush pilots I made them for, actually removed the ELTs from the plane and carried them up to the top of a hill and Set the Elt on the ground and hung the twin lead up in a tree to
Get a better signal out so help could hear it
The antennas only weighed a few ounces and rolled up to
The size of a dougnut but could save your life ....... You can cut one for 406mhz just as easy. I should probably start building some this winter.??? I am still running 121.5
And an inReach.

TurboBeaver said:

Little late for this, but years ago I used to make up roll up antennas out of TV twin lead, in the ham radio " j pole" style, with a BNC connector and cut for 121.5.mhz.
Many times when you wreck a cub the ELT antenna is
broken off. So you simply unhooked the broken coax, that
was hooked to damaged antenna. Unrolled the twin lead J
Pole and hooked it to the ELT and BINGO you were now transmitting on 121.5.
Lots of bush pilots I made them for, actually removed the ELTs from the plane and carried them up to the top of a hill and Set the Elt on the ground and hung the twin lead up in a tree to
Get a better signal out so help could hear it
The antennas only weighed a few ounces and rolled up to
The size of a dougnut but could save your life ....... You can cut one for 406mhz just as easy. I should probably start building some this winter.??? I am still running 121.5
And an inReach.

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Along that same line, some ELTs are available with small folding or telescoping antennas. They're usually stowed in or on the ELT to make them available after the crash. Like you point out, if you have damage to the coax or mounted antenna or need to walk out, a portable antenna is the only way of making the ELT 'heard'.

Web

I can think of a couple of Cessna accidents where the airplanes were on their backs in shallow water, yet the 406s transmitted. I’d bet if you disconnect your 406 antenna and set it off you’ll get a phone call in short order. And that begs the question... we know the ELT in the Ted Stevens crash came loose from the velcro mount and severed the antenna cable. Did any reports verify that the ELT was activated?

FWIW, not long ago I did some internet research about G switches in 406s. The current TSO specifies the same simple G switches that were used in 121.5 ELTs. I’ve never disected an ELT myself so I wouldn’t have a clue what’s in there. Are the 406 switches standardized between brands?

They use accelerometers now not G-switches. G-switches are mechanical designes. Accelerometers are electronic circuits designed to measure or sense a specific parameter. G-switches are mechanical designes. With G-switches you can set them off with a slap, bang it against the work bench, or smack it with a rubber hammer. Acceleromters will only trip with the throwing motion described in the installation manuals. I've tried all the old ways and they just don't work on the new styles. This reduces inadvertent activations but makes the susceptible to NOT activating when they come loose or are not mounted solid enough.

I agree that sometimes signal from the 406 ELTs do amazing things. I once had one ping a satellite from my workbench. But I'd never count on such an occurrence during a crash. Make sure to increase the odds in your favor in any way possible. I.e. quality ELT mounted correctly. Antenna mounted correctly with some sort of protection like the vertical stab to protect it on nose over. Coax routed directly from ELT to antenna and not crossing production breaks or know areas that buckle during typical crashes. And even including a portable antennas in case you find a need for one.

And don't forget proper testing, maintenance, and battery replacement.

I've never seen a mobile antenna with a 406. 121.5s used to have them but none of my 406s have.

Artex and Kannad both make them.

Web

234/406.1 x 12=6.91 inches of stiff wire on a bnc connector.....