A

apatti

Well Known Member
All,

I have heard of folks mounting their ELT antennas on 8's inside the cockpit where the front seat back support bar mounts to the side of the fuse. The antenna extends vertical up through the little triangle made by the support bar and the side of the fuse. Does anyone have any experience with this? Does it get in the way? Any poked eyeballs? Also, any pictures of this installation?

I also know a lot of folks have mounted their ELT antennas horizontal under the emp faring. I am still considering this. However, I am unsure how to get back there to secure the coax. In addition to the elevator bellcrank, I have the AHRS (and associated plumbing) and the autopilot servos in the way. I just don't see how even a scrawny guy (which I'm not) can get back there to secure the coax past the 809 bulkhead.

If it matters, I have the Ameri-King 406 ELT.

Thanks,
 
The pic shown in the link above is a good example of how not to mount an ELT antenna. It's clamped virtually on top of aluminum structure. As a result its radiation pattern will be very highly distorted. We hear so many people talk about the poor track record of ELT's. Installations like the one shown in the picture make poor ELT functioning a foregone conclusion. Same goes for the installation under the empennage fairing for the same reasons.

Get the antenna outside, away from other metal surfaces and as close to vertical as possible. The installation space available on a -8 is minimal, I know. But there are other options. One that works a little better is to place the antenna back on the empennage, between horizontal and vertical stab so that it pokes out at about a 30degree angle from vertical, maybe 45 degrees, forward far enough that it gets bent backward when the canopy is slid all the way back. Put some heatshrink tubing over the antenna to ensure it doesn't mar the finish on the canopy. It's not perfect but it's a long way ahead of either the pictured installation or the suggested empennage fairing installation.

BTW, I make these comments as an avionics guy who spent a decade or more working with some top-notch electromagnetics gurus and I've installed just about every kind of antenna you can think of on airplanes ranging from homebuilts to widebodies to fast-movers to just about any helicopter you can name. My comments are based on the desire to ensure nobody sacrifices ELT functionality in the name of vain esthetics. Sorry if they get somebody's dander up, but I'd rather an ELT be given every possible opportunity to function properly because we only use them when we really, really need them.

'Nuff said. Spock out.
 
I am mounting mine vertically from the top of the Vert Stab fairing with nothing to get in the way...yeah, yeah, if the plane flips the ant is in the dirt, but if it doesn't its in the best position possible....plus it actually conforms to the installation instructions ensuring compliance with the TSO..my two cents.

Ken
 
Well, I am certainly not going to disagree with a radio guy, but you asked where others have mounted their ELT antennas, and specifically about the rollbar mounting. Whether this placement is good or bad is up to you (or others) to decide. I really don't care. This is how I did it...


ELT1.jpg


ELT2.jpg


Rubber ducky antenna from my Icom handheld. It doesn't interfere with the canopy at all, and you'd have to work really hard to stick yourself in the eye with it. :D

Hope that helps.
 
Well, I'm still a ways from installing mine, but I have heard the arguments against the fairing area.

But I also take exception to one assumption being made...how do you know the airplane will be upright and in one piece when you need your ELT?

I'm not a "radio guy", but common sense tells me that mounting the ant. on the exterior of the aircraft makes it susceptible to damage during an accident--rendering the ELT useless. For that matter, as stated, the aircraft could flip and drive the ant. into the ground.

I simply posted one option. If you make an off-field landing and can walk away, you can unhook/free-up the ant. in the pic I posted and wait for the choppers to arrive. If your landing was severe enough to render you unconscious and/or the airplane is damaged, all bets are off regardless of where you mount it...too many variables/scenarios to KNOW a location is going to work EVERY TIME, IMO.

BTW, the ELTs on my on my "day-job" aircraft are in an overhead bin in first class...


Joe


PS. Don, I'm guessing Danny had you mount that there ;):)
 
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no good solution?

I've struggled with this question a lot.
The cabin brace area installation does not provide much of a ground plane. I suppose the cabin brace and fuselage rail make a 3-legged ground plane? I don't think you can use a rubber ducky with the 406 ELT - you have to use the supplied antenna. The one I've seen is angled about 20 degrees, has several inches of composite blade, with a wire whip extending from that. I wonder if that would fit inside the canopy if the 20 degree angle was tipped inward from the rail toward the centerline?

If you flip upside-down, you need help right away. If you stay upright, you probably don't need help so much. So that logic would suggest mounting it on the belly.

For the 406 ELT's, the installation is much more strict, because it needs to find satellite link. I think I've heard that the ELT will issue an antenna fault warning or something if it can't get satellite access. ( can someone confirm or deny that?) So this means that regardless of logic, its gotta point upward.

Hate to point out that a pretty good place from a functional standpoint, is right in front of the canopy on centerline. I know, this sucks because its right in the field of view all the time. But it would be protected by the roll bar in a flip-over, it has a good symmetrical ground plane, is pointing up and perpendicular to the ground plane, and far enough from the roll bar to not mess up the radiation pattern (too much). But asthetically, it sucks.
 
ELT Location

We definitely need some help from a qualified person here. Although I am an EE, and have a rudimentary understanding of radiation patterns, I don't have enough experience in the area. I won't let that stop me from sharing some thoughts though.

I think the rubby ducky near the roll bar is a reasonable idea. It should be a well protected area. We can't predict in what orientation an aircraft will come to rest after an accident.

I've thought about electrically isolating the antenna and have it placed along the leading edge of the vertical stab.

Perhaps mounting it in the rudder fairing would be good, but lends itself to difficulty with the antenna wire moving.

The best place of course is to have it vertically mounted in the largest flat plane area possible. But let's face it... there is no perfect place. Perhaps someone who has the equipment might try a few areas and measure the field pattern. It's sure to be blocked in some areas wherever you mount it.
 
Top And Bottom

I know nothing about ELT antenna or there installation, but I have a question. Can you put two antenna's on one ELT, one on the bottom and one one the top then it wouldn't matter what orientation the plane ends up in? I am going to guess you cant or some one would have done it. what about two different ELT on the same plane if you cant use one ELT with two ant. Like I said I know nothing about this subject but I am doing a little research.
 
Two antennas

You would need an appropriate splitter and then each antenna is only radiating at half power (or less due to splitter losses).

I wouldn't do it.
 
I gave this a lot of thought and decided to mount mine under the emp fairing. Why, history shows ELT's (121.5 history) are highly unreliable for crash detection. You cannot predict what attitude the aircraft will come to rest in. I put my ELT in only to placate the FAA regs.

If my life depends on being found then I think APRS(my choice)/SPOT and a PLB strapped to my shoulder harness is my best bet.

Again, only the choice I decided to make.
 
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Like Wade, I put the ELT in to satisfy the regs...period.
To possibly save my life; I put a PLB with integrated GPS (McMurdo FastFind 210) in the pocket of the fishing vest I wear when I strap in. The vest also holds my handheld radio, signal mirror, laser flare, and other assorted kit (extra batteries, etc.).
 
if you are installing the ELT just for the regs then I believe you also are required to install the the ELT and ant in accordance with the manufacturers instructions in order to comply with the TSO which probably states the ant must be mounted vertically on the upper surface of the airplane.
 
Just checked out the SPOT everyone raves about. Really cool system but I don't see this as a replacement for the ELT for emergency services. Certainly a nice enhancement. The problem I see is that it requires pilot action to notify 911 through the push of a button. While you may think you'll have the Situational Awareness to push the correct SPOT button PRIOR to the landing/crash..you may not. Do you keep your spot in the pocket of a vest requiring several steps just to get the thing out? Its small too, are you going to be fumbling to get a hold of it, verify the correct button and have time to activate it? you have an engine failure during take-off from a remote site at less than 1000 ft you are going to be 100% focused on the airplane, as you should be. Taking your eyes off the task of flying to fumble around your vest, pocket, or map case, to push the SPOT 911 button is PROBABLY going to add to the severity of the accident therefore negating its perceived benefit.

Don't get me wrong. I'm going to get one. But I'm also mounting my ELT ant correctly, because having located several downed aviators using Direction Finding derived from their ELTs I know the system works when installed correctly. Its not perfect, and it won't save everyone but the percentage is greater than 0 and since its required might as well give it a chance to do something other than add dead weight.

Im out
 
Now I see why I am having trouble with this decision. There really is no feasible solution given all the constraints. According to my manual:

"Locate the antenna at least 30 inches away from other antennas, wires, vertical stabilizers, etc. to minimize distortion of the radiated field and interference with other equipments. The antenna must be installed VERTICALLY (within ? 15o of the vertical plane is acceptable). Ameri-King has no performance data for installations that deviate from the stated requirements."

Well, vertical AND 30 inches from the vertical stab precludes anything on the aft section of the fuse (unless you only want to open the canopy about half-way. Mounting it in front of the windscreen is not advisable since it is less likely to survive a crash (besides being annoying and ugly). Anything inside the cabin is going to have a "who knows" radiation pattern.

Does anyone know if a highly distorted radiation pattern would manifest itself in a high VSWR? Perhaps we could test our installations that way. Otherwise, it seems to me we just put the antenna someplace convenient and "hope" it works when the time comes. Not a comforting thought.
 
Hi Folks,

I have an 8 and is almost ready to fly (I will fly it after receive my training on January 16th with Alec DeDominics) but only thing still missing is installing an ELT.

Chilean FAA (DGAC) requieres that ELT must be installed in agreement with fabricate intruction so my antenna must go vertically in the after upper part of my plane away from the tail obstruction.

Anyone knows how to install the ELT following all regulation on an 8:confused:

Happy Flyings and Merry Christmast
 
I mounted my ELT ANT on top of the Vertical Stab attached to the top most rib with a hole and grommet for the ANT wire to protrude from out of the fairing. It is out of the way and is vertical.
 
ELT Antenna Type?

Does anyone have experience with a rod or blade style ELT antenna on the RV8 vs. the usual whip style? Would this style allow a fit in front of the VS? Realize they cost more...just exploring options.

Thanks,
Mike
 
RV8R999 said:
I mounted my ELT ANT on top of the Vertical Stab attached to the top most rib with a hole and grommet for the ANT wire to protrude from out of the fairing. It is out of the way and is vertical.
Click to expand...

Until an unplanned landing in a soft field which will usually result in the plane flipping over on its back with the vertical stab in the ground..........but I'm sure you have already considered this possibility. ;)

There really isn't any "legal" way to mount an ELT antenna on an RV-8. Fernando, wish we had a good answer for you--let us know how you work this around the Chilean regulations.
 
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Just a thought (and my -8 is still at Van's): Are the blade antennas for 406 MHz ELTs short enough to fit on the skin under the canopy, right behind the back seat?

Edit: Just checked the prices, while I was looking for the physical dimensions. Ouch! Maybe that's not such a brilliant idea ... :eek:
 
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Sorry, no

hendrik said:
Just a thought (and my -8 is still at Van's): Are the blade antennas for 406 MHz ELTs short enough to fit on the skin under the canopy, right behind the back seat?
Click to expand...

Unfortunately no. Since they also transmit on 121.5, the 406 antennas are about the same length. The one I looked at has a partial blade, partial whip.

BTW, putting it on top of the fin is just about worthless!

In front of the windscreen is actually pretty well protected because of the roll bar. It would survive almost all conceivable crash scenarios. (scenari?) Too bad it would be so annoying. My first glider was a Schweizer 1-26, and it had a total-energy venturi on a strut right in front of the canopy. After a while, I didn't notice it. So maybe a thin blade/whip ELT would not be very noticeable either.

There is common sentiment that ELT's are so unreliable that you just want to go through the motions to meet the reg's, then do something else for real rescue ( PLB, spot, etc). This is mostly anecdotal, I don't really know. I have heard that ELT's have been 'rescued' out of landfills, having no antenna attached! Mine have always worked when I tested them.

But the 406 ELT's are much better in all regards. If we could get a good antenna location, they would be a good choice in all regards.
 
you are hardly in a position to determine the "worth" of placing MY ELT ant on top of the VS as it does two important things:

It is in compliance with regs (where is yours located BTW? Hmmmm)

And it is out of the way and looks good to me there. Since I don't plan on needing it, it will spend most and hopefully all of its life up there, out of the way, in compliance and looking far better than under the windscreen.

will my RV8 tip over during a soft field landing rendering it useless..maybe, is that likely? I don't know the stats, does anyone?

It is ridiculous to even debate the best possible location based upon the multitude of possible accident scenarios so the criteria I used were regs and how it looks and both are worth something.
 
I don't think top of fin complies with regs

When I read the install instructions for my ELT, the instructions that must be complied with to satisfy the TSO, there is pretty clear language about not installing the antenna on extremities that are easily damaged in an accident - in words to that effect.
 
yes , but the word "easily" is very vague and not enforceable as per the TSO, since nobody can predict the outcome of an accident. However the words, "outside and on the top of the aircraft" and "in a vertical orientation" are specific and well defined criteria. The instructions for my ELT make no mention of the extremities or how easily the ANT might become damaged in an accident - which is totally unpredictable.

BTW Where is your ANT located?

So here is a question for an EE - If you installed two ANTs, one on top and one on the bottom of the plane, using a splitter and had an accident in which one of the ANTs was destroyed and the other is ok. Would the signal strength still be reduced because of the coax connection through the splitter? Or would the damaged ANT appear as an open and allow the functional ANT to xmit full power?
 
It will entirely depend whether or not the damaged antenna/cable shorts or goes open. At the best only half of the signal will reach the remaining good antenna.
 
RV8R999 said:
So here is a question for an EE - If you installed two ANTs, one on top and one on the bottom of the plane, using a splitter and had an accident in which one of the ANTs was destroyed and the other is ok. Would the signal strength still be reduced because of the coax connection through the splitter? Or would the damaged ANT appear as an open and allow the functional ANT to xmit full power?
Click to expand...

No, it would not work. A splitter will need to see an appropriate load on each of its outputs. Have you ever seen the splitters used in your cable TV wiring at home. Note that (if it was done correctly) there is a 75 ohm dummy load on any unused ports of the splitter. A broken antenna on either port of a splitter will impact the operation of the other antenna. To the point that it won't work?? Who knows? It depends on the damage to the antenna and the resultant load it presents to the transmitter. But you would already be cutting your signal in half with the splitter.

The only real way to do have a two antenna system would be with intelligence in the ELT itself. It would need two antenna ports and automatically switch between the two from time-to-time. Perhaps it could even sense a high SWR on one of the ports and stop using that one. I guess this could be done with an external box as well. Sounds like a good project for someone out there who understands all the Greek letters used in RF antenna design.
 
I'm just monitoring this discussion, I have no regs or instructions to reference, but why can't it go on the bottom? While there are no doubt limitless possibilities of how a wreck might come to rest, it seems to me that if you end up upright with minimal damage to extremities, it's likely you're ok enough to phone home. If everyone assumes you'll flip, why not put it on the bottom where it'll be out of sight mostly until you wreck and flip, then it's perfect?
Inquiring mind out here.
Clay "Cookiemonster" Cook
N838CM
 
Mr. Cook has it correct I suppose other than on the RV-8 that went down a couple months ago. I seem to remember some photos showing the plane standing on it's nose with the tail straight up. Now we can only guess how many times that happens conpared to flip overs and crunched up spam can smackins. Still, we all want to do it the "BEST" way possible. I mounted my ELT antenna under the fiberglass empenage cover to the side of the HS and HS. Sometimes we just have to say the plane is Experimental and hope we guess correct. Next guy to pull off some wings without setting on a parachute will ask himself "why did I not invest that money in a BRS"? instead of "wonder if I mounted my ELT antenna correctly"?
Best to the rest, Bill of Georgia RV-8a wiring
 
Upon much consideration I believe the upside down mounted ELT ANT probably is as good as it gets and should satisfy my two stated goals even better.

So...thanks for the discussion and great ideas..I'm moving it from the top to the bottom and it'll be a lot easy to mount now too :)

Its still not worthless on top though :)
 
I was reading my Ameri-King manual last night (strange I know) and found this:

2.2.2.2.4 Integral Antenna Installation: (451017-4S)
The integral Antenna 451017-4S is fastened to the ELT-(AP), ELT-(S). This antenna required no ground plane. The antenna ground plane installation is not required.

The Ameri-King ELT package I purchased from Aircraft Spruce came with both the whip antenna (ground plane required) and this integral antenna. This antenna is designed to plug directly on the ELT so you can carry it with you if you leave the crash site. Thus, it doesn't require the ground plane. The integral antenna is about 2.4 inches longer than the whip. I plan to use it for my inside the cabin installation. I just need to come up with a non-metallic standoff contraption to secure the top part of the antenna a little better.

Thanks for the discussion here.
 
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