On Monday, September 10, 2018 at 6:21:06 AM UTC-6, Martin Gregorie wrote:
On Mon, 10 Sep 2018 01:35:01 -0700, flybd5 wrote:

I saw make electric winches and put huge wind turbines next to them to
recharge the batteries.

Actually, the turbine would be fairly small.

A winch launch takes about 35 seconds from first movement until release
and about the maximum launch rate achievable with a two drum winch is 20
an hour[*], so the winch duty cycle is 20% at the most. If we assume the
winch burns a continuous 300kW during a launch (yes, that's probably a
large overestimate), then the average draw over an hour is 60kW - well
within the capability of a diesel trailer generator or a 22m diameter
three-blade wind turbine.

If the winch averages half power over the whole launch and the launch
rate is a more typical 10 an hour, the average power requirement drops to
15kW or a 9m diameter three-blade turbine.

The rule is simple, if you can land through the blades the launch
is free.

... but an glider bigger than about 5m span would not fit through the
blades of a suitable turbine, even if it was stationary.

[1] Several years ago a bunch of us made periodic attempts to see how
high a launch rate was possible with a two drum diesel winch (Supacat).
We could hit 20 launches an hour, but never managed to exceed it, and
apart from the winch driver and launch marshal, we needed a full-time
driver in the cable retrieval truck, and another two people to collect
gliders as they landed, put them back on the dual launch queues, and keep
the launch queues moved up to the launch point. It didn't need much to
drop the rate either - an instructor who briefed when he and his student
reached the front of the queue, rather than one or two launches earlier
would do it.


--
Martin | martin at
Gregorie | gregorie dot org

The numbers are simpler if one uses 1 - 2 kWh per launch (depends on glider weight and height of release) so 20 launches an hour would need a continuous 20 - 40 kW supply to maintain a steady-state battery charge. With a battery buffer, this supply can be very unsteady. The max power demand is not as important as long as the battery can deliver it.

40 kW is well within the range of various renewable sources. The incredible drop in solar panel prices make that a reasonable possibility. I estimate it would take about 2,500 sq. ft of them (~$25,000). One can imagine an accordion package which could be spread out on the ground near the winch.

While on the subject of dropping prices, Battery costs are dropping so fast that one can imagine a pack large enough for a whole day's winching. Recharging overnight from grid power simplifies the whole idea of an electric winch. Further imagine the winch mounted on an electric truck using the truck's enormous battery pack.