[Scott Will]

Anyone ever put an ELT antenna on the forward side of the firewall? I moved my ELT yesterday to help out with CG issues (Catto prop only 17 lb). I'm thinking of putting the ELT under the cowl. Many people put them under the fiberglass fairing on the tail... but routing the antenna will be really easy for me on the firewall.

 

[szicree]

Seems like in a wreck this area is gonna take a beating. The orange box might still work, but what about the antenna wire?

 

[MarkDews]

ELT Location

I see that you have a tip up canopy.

Are you going to be able to access the ELT easily after you rivet that forward skin?
You need to access it at least annually to replace the battery.

I considered this (and still am!). I have a light wood prop.

I also agree that the antenna might take a beating up there.
A little extra slack in the antenna cable and mounting the antenna securely might alleviate some of that issue. If the firewall is that distorted, what are your chances of survival?

Mark Dews
RV6A N885SM

 

[Scott Will]

I'm going to cut access panels like Dan did so it will be totally accessible. (Obviously thought of this)

A lot of people put the antenna in the tail.. what if the tail is torn off in a crash or the antenna line broken?

I'm considering making the access panels out of fiberglass so maybe I can put the antenna on the cold side under the glass access panels.

 

[MXpilot1]

I believe the ELT you show is made to be removed from it's mounting upon a crash and carried with a survivor if they were to walk away from the crash site. That may be difficult if the ELT is under the cowel.

 

[gmcjetpilot]

I'm going to cut access panels like I'm considering making the access panels out of fiberglass so maybe I can put the antenna on the cold side under the glass access panels.

I think the flush hidden panel is cool for a GPS looking up, but we are talking a 18"-21" whip with vertical polarization.

Reference to picture below says the windscreen and top deck behind the firewall may not be a great location. In the scenario below, the cowl is looking better, well at least if it is mounted on the side or bottom (now top) of the cowl. Again there's no "standard" crash, so it is hard to say. However with the engine in the way, it's fair to say the cowl is not an ideal location in any attitude the plane ends up, but may be no worse than say in the tail fairing which is blocked by the Vert and Horz stabs. However the tail is more likely to be in tacked.


You can put the antenna anywhere but just for grins the recommendation of the ELT manufacturer's and FAA standard practice for the ELT antenna is:
-Mount as far aft as possible
-With in the same "Bay" (between same bulkheads) as the transmitter
-External vertical antenna installation, top of fuselage (I know, ugly. I don't want that either)
-Lanyard between antenna base and transmitter recommended to avoid coax damage if airframe distorts
(I did not write the above only paraphrased a couple of "official" sources)

No matter where you mount it, the fuselage is likely going to block it to some degree. The wisdom of the manufacture to mount the antenna aft, top, external and vertical is evident in this Pic.


Picture is from: http://www.vansairforce.net/articles/Imitutor.htm.


It should be said an external ELT antenna is only going to be a 1/3MPH drag penalty at 200 mph, may be less. Of course external antennas don't always work either. Many a "factory" ELT has failed to work. I suspect it's for many reasons, and the antenna is only one part of the many reasons ELT's don't work when needed.

Wing tip may be(?) better, but no guarantee it will not be torn off in a crash.

Depending on where you mount the ELT some what determines the antenna location. Long coax runs are a NO NO.

My choice is inside the aft cockpit. It's in the way somewhat and visible but think it will be better protected and transmit further than other "hidden" locations. My ELT transmitter is planned for behind the seats on the baggage compartment floor with a short coax run (with some slack) going to the antenna above. The whip antenna extends above the fuselage side, but behind the plexi. This is shown in the picture I modified above. This area of the plane should be not compromised in a survivable accident. Even upside down the antenna should still see some sky. Its easy to do this with a tip-up with the fixed roll bar and fixed baggage compartment windows, but still possible with the slider. Forward ELT location will help not aggravate an aft CG issue that some RV-7's have.

For light RV-7's needing weight forward the ELT Tx'er place under the panel or just under it on a tray is a great location. The coax can still be run under the center system tunnel and up the side walls behind the seats to an aft cockpit antenna.

George RV-7

PS

In a few years we will be going to 409mhz. Since 121.5 is retained the antenna will still be long or you will get two antennas. The 409 antenna alone is real small and would be easy to hide, but with a separate 409 antenna you than still need the second 121.5 antenna. The combined two in one antenna of the Artex is nice and looks like a typical 121.5 center loaded 18" whip.

 

[az_gila]

FARs

George's previous comments about the ELT location are not quite strong enough. It's not a "manufacture's recommendation" it's actually a FAR.

Sec. 91.207 - Emergency locator transmitters.
(a) Except as provided in paragraphs (e) and (f) of this section, no person may operate a U.S.-registered civil airplane unless --

<big snip>

(b) Each emergency locator transmitter required by paragraph (a) of this section must be attached to the airplane in such a manner that the probability of damage to the transmitter in the event of crash impact is minimized. Fixed and deployable automatic type transmitters must be attached to the airplane as far aft as practicable.

Whole thing here..... http://pilotfriend.com/FARS/30/Sec. 91.207.htm

Even as Experimental aircraft, we have to meet TSO stuff for ELT's and transponders.

Think twice before mounting the ELT up front. Can you honestly say it's "attached to the airplane as far aft as practicable"?

George said to be honest with the tax man in another thread.. be honest with the FARs too...

gil in Tucson

 

[gmcjetpilot]

Yea I did

George's previous comments about the ELT location are not quite strong enough. It's not a "manufacture's recommendation" it's actually a FAR.

George said to be honest with the tax man in another thread.. be honest with the FARs too...

gil in Tucson

Thanks for keeping me honest and agree with you but I have a different interpretation. I think I covered my bases. We are talking about antennas right? FAR's especially part 91 does not really address installation in detail. In fact it only makes a few wishy washy references, I highlight below.

As far as FAR's, my previous bullets are right on, even tough I did not refrence the FAR directly. However I do think the real devil is in the details, and those are in installation instructions for the TSO'ed ELT.

If an AP installs an ELT in a factory plane they will follow the FAR's but will follow the manufactures recommendations which are TSO'ed and much more detailed and are really binding. You MUST follow the instructions for a TSO installation in a factory plane. Do we (RV'ers) need to meet the TSO? OK lets say we do.

Now for the CLOUDY FAR's:
-----------------------------------------------------------------------------------------------------------------

The only significant par about the antenna is:

"(4) The presence of a sufficient signal radiated from its antenna." (says nothing about where or how to mount it)


The second Par of significance regards the ELT Tx'er location not the antenna:

"(2)(b) Each emergency locator transmitter required by paragraph (a) of this section must be attached to the airplane in such a manner that the probability of damage to the transmitter in the event of crash impact is minimized. Fixed and deployable automatic type transmitters must be attached to the airplane as far aft as practicable." (what kind of word is practicable, only in the FAR's )
-----------------------------------------------------------------------------------------------------------------

However who is to say what is practicable? (feasible, possible, Usable for a specified purpose). Hey if your CG calls for all equip mounted forward of wing spar than under the panel is OK. It looks pretty safe there? Why not? Are there other areas in the plane that provide "probability of damage to the transmitter in the event of crash impact (to be) minimized"? Sure. How aft does that need to be?

From the above we MUST mount the ELT practicable aft, usually the tail cone. Sure why not. It is probably the best place from common sense. More specifically you will follow the ELT manufactures recommendation.

Why is my ELT in the baggage compartment not the tail cone? One thing it is as far aft as practicable and unlikely to be damaged in a crash!!

EBC makes an ELT (TSO'ed FAA approved) with an integral antenna for in cockpit mounting, right. It has to mounted in the cockpit and so that is as far aft as practicable. http://www.wingsandwheels.com/page13.htm

My theory is I want the ELT antenna with a window view to the outside world thru the plexi canopy (just like you get with an EBC unit). To keep the coax short and still provide protection to the ELT transmitter, the baggage compartment is as FAR AFT AS PRACTICABLE! It works for me.

Mounting the ELT on the floor, protecting it from being hit with a cover and mount the antenna nearby, as I show in the flipped RV-6 picture, I think meets my installation instructions and intent of the FAR's.

My ELT's generic "TSO'ed" instructions, recommend a typical ELT location aft of the baggage compartment but must be able to access it (to remove after accident) and antenna be near it. The antenna needs to be mounted external, top and vertical. My cockpit mounted ELT antenna is on "top side of the fuselage", external (at least electrically thru the plexi) and vertical? That's my story and I am sticking to it. Since EBC has the same antenna location for their ELT's, if it works for them.........

I am playing a game with you, but builders do mount ELT stuff any old goofy way that may not meet the spirit of the Regs or installation instruction. Why? To hide it and gain 1/3 mph.

People also get philosophical about ELT's, like if I crash I am dead and if not, I'll get out and use my Cell phone or other rationals. I don't feel that way. I want to give it a good "practicable" chance and attempt to meet the spirit of the rule and Regs.

Does an ELT under the panel meet the Regs? I guess you could make a case for it. What about antennas burred horizontal under fairings, cowls or wingtips. Uhaaaaa probably does not meet standard antenna installation instructions like: external, vertical, top of fuselage, close to the transmitter. So I agree with you, but think I meet FAR 91 and TSO'ed instructions. Again that's my story and I am sticking to it.

George

 

[swill]

Is it practical to put the ELT so the CG is further out the back end and further decrease stability?

 

[McFly]

I took a physics first approach

Is it practical to put the ELT so the CG is further out the back end and further decrease stability?

That is my read as well. I too will have the aft CG issue due to a light prop. I mounted the ELT between the firewall and subpanel, the anntenna is against the roolbar (tip up) and mounted on the gussett.

IMHO there is no sence mounting it in a place that will increase the probability that it will be activated Then again I regard ELTs as a $200 2.5 pound brick.

 

[az_gila]

Dar?

Perhaps "Mel DAR" could chime in and say what a DAR looks for in the ELT installation when he checks a plane for conformance to regulations and airworthiness?

gil in Tucson