Installing the ELT in the firewall

Hi,
i have searching the forums to get info. about where to install the ELT antenna in the RV-8. It seems there is not a good place.
In the last Sun & Fun there was a Kannad ELT with internal GPS and 406 Mhz. antennas . The weight is 755g and the dimensions 140mm x 98mm x 86.4mm.You can get more information in

http://www.kannadaviation.com/index.php/ga-fixed-wing

I?m thinking about installing the ELT in the upper side of the firewall. the same place many builders and Van?s in the RV-12 install the GPS antennas.

I appreciate comments about this location.

Jose del Peso
RV-8 (#80971)
Electrical

ELT antenna

No I don't think there is a really good place to mount the ELT antenna on any RV. It needs to see the sky (through RF transparent material) or should be mounted externally on the upper fuselage. However it should not be in a location that it can be broken off during an accident, so externally on the upper fuselage is vulnerable. The best place I have seen and plan to use on my RV is horizontally above the horizontal stabilizer under the fiberglass fairing between the horizontal and vertical stabilizers. The fiberglass is RF transparent and it is protected from being broken off. It is not perfect as the antenna should be mounted vertically, but who can tell what position the aircraft comes to rest in an accident? If you survive the accident you can remove the fiberglass fairing and mount the antenna in a vertical orientation.

So the firewall location is probably too close to the scene of an accident to be counted on to survive, even though the cowling is fiberglass.

And then there is the legal "sign off" issue. The location by the horizontal stabilizer may not satisfy the inspector. In this case, a copper foil antenna can be fabricated and mounted on the inside of the canopy. The side by side models are easier for this, but still could be done on a -8.

I have seen several installed in the passenger cockpit, at the rear of the right armrest. (same location as flap linkage, opposite side.)

make me smart

Don't these antenna's need a ground plane for effective operation??

My current install (behind the seat on the baggage compartment rail) doesnt have one. Those under the emp fairings dont have one.

Any good ant people out there with an answer. I think the answer will be an inconvenient truth.

Is there another antenna form (like an archer nav antenna) that will work??

The answer is indeed an inconvenient truth. Do some searching around by other posts on this topic and you'll likely see a few of my posts. The RV is a small enough airplane that finding antenna mounting space is tight, and even more so with a sliding canopy which virtually rules out placing the antenna on the top radius of the fuselage.

I've done enough RF testing to be able to say that installation under the fairing is almost certainly a poor choice. You would in many instances be better off installing it near the aft end of the baggage compartment or someplace similar where the antenna can clear the sliding canopy and still have access to a nice adjacent chunk of skin to act as a ground plane.

Installing forward of the firewall is just a bad idea, plain and simple. That's where all your flammable fluids are, and also where most impact forces are concentrated. Probability of survival of the ELT is low.

Now I'll throw a little heresy into the discussion by suggesting that an ideal solution would be the Kannad ELT with built-in antenna, mounted on a shelf in the upper radius of the fuselage (now here comes the heretical thinking) under a honeycomb composite skin panel. You could build the composite panel to have at least equal strength as compared to the original aluminum skin, particularly if you went to beefy edgeband closeouts. And you've have a fantastic place to mount the ELT with its integral antenna, as well as any GPS antennas you migh want to install, not to mention XM or other satellite-based systems which use a flat patch antenna and need a clear view of the sky.

OK, now that I've said it I'm battening down the hatches and donning my nomex suit! ;-)

Pondered this quite a bit before I decided to mount it on the belly on the aft fuselage. Not ideal, but with the likelyhood the airplane will be on its back after a crash pretty high, better possibility of radiating than any other location on an -8.

The fact is, there is no "good" place on an -8 with a full slider canopy.

Thanks everybody for the information.
There is not a good place to install de ELT in the RV-8.
I think that the Kannad with the internal GPS and 406 Mhz antennas, the size and weight offers some new possibilities. Maybe I will consider installing it in the wingtip or in the cockpit between the two pilots seats.
Thanks again .
Jose del Peso