On 8/24/11 8:44 AM, Paul Remde wrote:
Hi Dick,

ELTs are still great safety devices.

Most contests probably won't require them - requiring SPOT units instead.

One workable internal antenna mounting solution is shown he
http://www.archive.jimphoenix.com/ar...Nfuselage.html
[snip]

I might dispute that an ELT is a "great safety device". They are very
hard to install properly (as the link provided demonstrates very well).
A 406 MHz ELT is a useful distress signaling device if people are aware
of their limitations, and if they are installed properly. And there are
very high activation rate failures--people should just not assume these
will trigger automatically, especially given many of the (unavoidable)
improper installations in gliders. I strongly believe that alternative
technologies including SPOT and/or 406MHz PLBs provide better safety
benefits for less hassle/work/effort/cost. You can buy both a SPOT and
PLB and have money left over compared to a 406 MHz ELT. 121.5 MHz only
ELTs are really not even worth discussing. Spider and other technology
at more expensive price ranges an do even more (and things like the
Garmin GSR-56 are very impressive for high-end GA aircraft).

Workable ELT antenna installation? Sorry but but I can't let this slide
by a "workable install". I know it is very difficult to mount an ELT
antenna on a glider and there are always serious tradeoffs but I don't
want anybody thing the install shown in the link provided really is a
good installation of an ELT antenna.

At least the forward cockpit here is glass fiber but bolting an antenna
on to metal rod going off at 90 degrees from the antenna base is not a
suitable ground plane. The radiation pattern from that is antenna will
be highly directional and weaker than a proper ground plane
installation. A ground plane for a 1/4 wave antenna should be a
conductive disk (or metal screen) or close shape of radius at least the
same as the length of the antenna. Alternately radial wires or rods the
same length or longer can radiate in a disk pattern from the base of
the antenna. You might be able to get away with as few as three
symmetrical ground wires, but four is more usual. And you also need to
get the antenna above any carbon fiber surfaces and an antenna length or
more away from significant sized conductive objects.

So basically you can't get these antennas to fit inside a sailplane and
any install will be a significant compromise. Many of the ELT
installations I've see in gliders are very bad. I would be very
disappointing if ELTs were ever mandated at a contest. You would have
people badly installing these boxes just to comply with a rule. If the
goal was providing reliable, effective emergency signalling you would
have the poor CD and staff needing to reject glider entries with
horrible installations (which might be most entrants).

BTW checking you can hear the ELT over the radio on a nearby receiver is
a next to useless test of ELT antenna performance.

Darryl