Bill Daniels wrote:
There are electric winches that can launch a glider to 2000' AGL - it takes
about 1KWh. From that, I would expect that an electric tug would require
more than 5 KWh to do the same job since it is launching both the glider and
itself and must have reserve power to return for landing.

A problem for both the electric winch and this hypothetical tug is the
availability suitable power on the flight line. To recharge in a reasonable
time, you are going to need serious power service - maybe 440V 3-phase 200
amp service. That's not trivial to work with.

The only electric winch I've seen specs for, the ESW2B,
http://www.startwinde.de/, solves that problem by consisting largely of
a bank of heavy duty 88 AH SLAs. These act as a buffer between the mains
supply and the winch motor, a 200 kW unit. This buffer allows continuous
launching off a (typically) 12 Kw mains supply. Stated power supply
requirement is anything between 7 and 20 kW, which probably reflects the
average launch rate throughout the day. 12kW is still around 30 amps:
not trivial, but a lot easier to deal with than 200.

Of course, its still expensive to put in buried cables to the winch
positions, but as an interim measure I should think that the winch could
be driven off a trailer mounted generator.

For example, we use five winch positions on our field, but almost all
launching is done from two of them. The fifth is almost never used. The
two most common positions and one of the 2nd tier positions could be
serviced from two power cables and it would make economic sense to
purchase a used trailer generator to cover the other two.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
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