....and haul/pump the water.

On 9/2/2018 2:37 PM, Chris Rowland wrote:
At 17:57 02 September 2018, Martin Gregorie wrote:
On Sun, 02 Sep 2018 09:15:40 -0600, Dan Marotta wrote:

Didn't the German winch require being hooked up to the electrical grid?
It seems the one currently under discussion would be self contained and
portable (on the back of a truck).

All the electric winch designs I know about (and I assume the new US
design is similar) require three things: a power supply, a large electric
motor and a battery bank to act as a buffer between the first two items.

The German Electrowinde winch needs a 12-20 kw mains supply to feed a
220kw motor via its battery buffer, so the batteries aren't just for
decoration.

It seems to me that the winch motor and battery bank capacity will be
much the same whether the winch is configured as a towable trailer, on a
truck chassis or built into a permanent building: they all need the same
three part power train and it really doesn't matter whether the power
source is the mains, a COTS 12-12kw trailer generator parked alongside or
a truck with all three items installed on it.

A major issue for a mains-powered electric winch, in the UK anyway, is
the cost of cabling the airfield. We looked at it some years back: there
are four places were we put our winch - normally on one end of 04/22 and
less often on one end of 16/34 (obviously this is wind dependent), so
we'd need to wire up all four points on the field with buried cables, and
the winch points for 34 and 22 are both around 1km from the club house
and hence the nearest mains supply. Wiring our airfield would be quite
expensive. Consequently, we've gone with a Skylaunch running on LPG
(cheap and environmentally benign fuel). And we already had the tractor
used to move it between garage and the day's winchpoint.

What's the point? Why not just use a piston engine for the winch then?

Because a (much) smaller engine driving a generator to keep the battery
bank topped up is probably more economical to run than a socking great V8
being running intermittently at high power, particularly when you include
the cost of wear and tear from temperature-cycling the big engine.


--
Martin | martin at
Gregorie | gregorie dot org
I hear there's an electric winch at the gliding club at Unterwossen in
Germany. AIUI it is very fixed - in a concrete bunker. The site is in a
valley on the edge of the Alps so launching is always in the same
direction.

I've wondered if the best way to launch is by gravity, a weight falling
into a mine shaft and attached to the glider by a cable. If you have a
supply of water then the weight is by filling a tank. At the end of the
launch you dump the water, pull the much lighter tank back up, then refill
it. Given enough room you could have a circular airfield round the mine
shaft. The only energy that you need to supply is to retrieve the tank and
cable.

A few things to sort out but it's a start.

Chris



--
Dan, 5J