The situation isn't nearly so gloomy!

Mark James Boyd wrote:
From what I can gather, the low-power transponders are 400mA
and encoder 200mA at about 12 volts.

My Becker and ACK encoder ~ 410 ma with no replies, and less than 500 ma
even in southern California airspace. A 5 hour flight is 2.5 amphour,
leaving lots of juice for the other instruments on the typical 7 ah battery.


The microfilm superthin solar panels about 1 foot square (12" by 12")
advertise 600mA at about 12 volts.

Sadly, the solar panels in my experience don't put out rated power
on typical days, with less than ideal sun angles (maybe really only
putting out 25%).

Put two on! But even one, with your assumption, means the battery has to
supply 1.7 ah to the battery, leaving ~ 5 ah in the battery for other
purposes. With two supplying 300 ma, the net transponder usage is only 1 ah!


Also, I suspect transponders underrate their power consumption,
and if flown in high jet traffic areas (where they get
pinged by ATC and the jets), probably consume quite a bit more.

Not true for the Becker. Ask a Microair owner about it's consumption.

So really one might be looking at 8 square feet of solar
array just for a transponder! Maybe a little hard to
implement on a glider without using the wing surfaces,
and the caveats that entails...

The Strobl panels used by the German manufacturers are very efficient
(http://www.strobl-solar.de/ - use the Google translation tools) and can
supply enough with less than 2 square feet. The disadvantage is the
cost, so most people would probably opt for another, or bigger, battery.


Well, it was a nice thought...

It _is_ a nice thought! People are doing it - it works!

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA