Revisiting ELT antenna placement on RV-8s

I posted this in another thread, but no one responded, so I thought I would repost it as its own thread. The lack of responses might be an indicator of what others think of the question, but I'm being serious:


Question for everyone: Does the requirement from the ACK installation manual that: "The antenna must be mounted
within 30 degrees of vertical, when the aircraft is in normal flight attitude" really preclude mounting on the bottom? Isn't it still "vertical" even if it is upside down?

In previous threads many have observed that if I'm upside down, I probably need help more than if I am right-side up, and I would want my antenna performing best then. But that is still a rationalization when it is required to comply with the TSO. But being oriented vertical, on the belly, doesn't that meet the letter of the TSO requirement?

I can imagine that the rationale for the requirement is that the antenna must 'see' the satellites. But I've observed GPS signals getting in and out with a variety of obstructions, so I suspect that mounted on the belly of the fuselage would still radiate out to satellites just fine (except maybe one directly overhead). So, functionally, I think a 406 antenna mounted on the belly would work just fine. Again, what do you guys think?

What do you guys think?

Mount it under the eppenage fairing and fly on. Base of the antenna attached to the last full bulkhead, the tip of the antenna held in place with a scrap piece of fiberglass.

Carl

As Carl said. I mounted mine the same.

Had a present this past Christmas morning.


During a storm, my unattended airplane (locked in a metal hangar) apparently activated the ACK ELT. I know this because the airport manager called me to advise that S & R was calling to verify location of emergency beacon. No external power to the ELT so the GPS integration was not active.

Based on this, you could probably bury the darn thing under your seat and still be fine ^)

Tom H.

No empennage fairing mount for 406 ELT

My current 121.5 ELT antenna is mounted in the emp. fairing as Tom and Carl suggest. But that simply won't work for the 406 antennas. Aside from failing to meet the TSO requirement, if you see what the antenna looks like you would realize it just wont fit in there.

The 406/121.5 combination antenna has a blade at the base, 6 or so inches long, then it has the wire whip extending beyond that. The length, shape, and stiffness of the blade at the base makes it impossible to fit under the emp. fairing.

Steve, I think you're on your own here. It appears that there is a real disconnect between the TSO instructions (which in an undamaged upright aircraft give maximum signal strength) and the probability of the antenna surviving at all.
Note: posted while you were typing the previous post. If it won't fit in the tail, I'd be reluctant to put it on the bottom. Too much chance of it being sheared off.

scsmith said:

My current 121.5 ELT antenna is mounted in the emp. fairing as Tom and Carl suggest. But that simply won't work for the 406 antennas. Aside from failing to meet the TSO requirement, if you see what the antenna looks like you would realize it just wont fit in there.

The 406/121.5 combination antenna has a blade at the base, 6 or so inches long, then it has the wire whip extending beyond that. The length, shape, and stiffness of the blade at the base makes it impossible to fit under the emp. fairing.

Click to expand...

The ACK 406/125.5 E-04 ELT antenna fits just fine under the empennage fairing.

Carl

I mounted my 406 antenna on the right arm rest in the back seat of my -8.

If you place it on the aft part of the arm reat the antenna does not have to be bent.

The only thing I did was place a small piece of velcro on the canopy frame so it would not scratch the paint or vibrate.

The backseater never has an issue with this placement.

Here's a picture, but now I'm going to run for cover because I know I'll be told six ways to Tuesday about how it won't work etc etc etc...

Tail intersection fairing ELT by Andy Karmy, on Flickr

You could try this,
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No reason it wouldn't work with a slider.

Like flying Greg

I did mine in an RV-8 with a stock sliding canopy like Flying Greg has in his photos above.

Don't think it matters

I mounted both the ELT and it's antenna in the right wing tip. Both are attached to the out board rib. The antenna is mounted near the leading edge and angled back to the TE tip, basically horizontal.

How do i know it works? While doing a periodic maintenance of the systems, i accidentally activated the ELT while in on the ground in the hanger. It had been a while since checking thing out and i couldn't figure out what the odd beeping was,,,,until Search and Rescue USAF Captain Good Guy called my cell phone and asked if i was OK. I asked for forgiveness and he wished me a nice day.

dbuds2 said:

I mounted both the ELT and it's antenna in the right wing tip. Both are attached to the out board rib. The antenna is mounted near the leading edge and angled back to the TE tip, basically horizontal.

Click to expand...

Wing tip antennas are great for concealment, but in the event of an actual accident, the antenna/cable is likely to be disconnected or damaged in that location.