Whether I would be able to mount the aerial internally
or not would depend on the engineer certifying the
installation. I understand that the latest generation
sailplanes with carbon fibre fuselages will have to
have externally mounted aerials, probably top or bottom
so that they will transmit both up tp TCAS equipped
airliners and down to Air Traffic Control. Although
the aerials are quite short, they do produce a significant
amount of drag. Remember that a 500 kg glider with
a 50:1 glide angle will only have a drag of 10 kg at
best glide speed.

I am not a tehnofreak, but I understand that Transponder
aerials have to be base loaded and require a metal
ground plane to work properly. Obviously not a problem
for a spam can or a metal Schweitzer glider, but something
else that has to fitted into the already crowded centre
section of a FRP sailplane.

Derek Copeland

At 01:12 02 September 2006, Eric Greenwell wrote:
Derek Copeland wrote:
Jack,

I know that a UK pilot removed a transponder aerial
from his glider part way through a Nationals competition
because he was losing too much performance in relation
to his competitors in similar gliders. Also I fly
a
Standard Cirrus, so I need all the performance I can
get!

You can't measure the performance loss that a transponder
antenna on
your Std Cirrus, the drag is so little; nonetheless,
the fiberglass
fuselage will let you mount one internally. The big
advantage is it's
protected from ground and handling damage.

--
Change 'netto' to 'net' to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download 'A Guide to Self-launching
Sailplane
Operation'