On Sunday, June 17, 2018 at 9:04:17 AM UTC-4, Martin Gregorie wrote:
On Sat, 16 Jun 2018 17:40:39 -0700, moshe.braner wrote:

But we're getting farther and farther away from soaring in the
discussion here. The thread about electric winches is more relevant.

Picking up on that, my club looked at the possibilities shortly after the
German ESW2 winch http://www.startwinde.de/ became available. Our field
was a WW2 bomber field. We use the triangle of runways between the
crossing points of the original runways (04/22, 16/34 and 09/27), which
wer dug out, the rubble used for build motorways and the runways widened
quite a lot and put down in grass. We normally fly on 04/22, because our
prevailing winds are SW and NE, less often using 16/34 if the get
northerlies or southerlies and rarely on 09/27 because its the shortest
and narrowest run. The consequence is that there are four places where
the winch is set up depending on wind direction, and so we'd need to need
to provide power at all four points.

The ESW2 winch requires a 400v supply capable of providing 7-20kW. The
cost of installing this cable made electric winching uneconomic for us.
The far ends of 22 and 16 are 1600m and 1250m from our clubhouse, which
would be the mains endpoint. While the supply for 34 could be taken off
the cable to 22 and the cable run to 04 is only 340m, these don't offset
the cost of the two longer cables or the possible upgrading of the club's
mains supply.

Since the ESW2 winch uses 1.2 kWh to launch an ASK-21 to 400m (1300 ft)
and its motor can draw up to 200 kW, there's a fair amount of battery
buffering onboard - I believe they use lead-acid truck accumulators. In
theory at least you should be able to run one off a construction-site
generator trailer rated at 7-20 kW and parked behind it, but I have no
idea how the cost of doing that compares with wiring up the airfield.

FWIW I think the original electric winches were installed at alpine
airfields which had a single runway and only ever launch in one
direction. Unterwossen has a four drum winch installation situated well
off the end of the airfield. IIRC I've seen photos of similar winches
installed in brick winch-houses. Of course this minimises the cost of
cabling, especially if the winch is at the same end of the airfield as
the club house and hangars.


--
Martin | martin at
Gregorie | gregorie dot org

Thanks for that info Martin. I am surprise it only takes about 1 KWH for a launch, that's the equivalent of 1/10 of a liter of gasoline, using the conversion number you gave above.

If the launch requires 200KW and the supply is 20KW then most of the launch power is coming from the batteries. That means that you could supply it with less power and it will still work, although it may need a longer time to charge between launches? E.g., if a launch uses 100 KW on the average and takes 1 minute (1.6 KWH) and you do one every 20 minutes (not ideal) then you need a supply of 100/20 = 5 KW.

BTW 5 KW of solar panels is only about $5,000 these days. That would do about 3 launches per hour. Possibly an alternative to running the expensive wires? (For only one location though.) Add more batteries and you can run the first few launches of the day on energy stored from the morning, the previous day, or overnight (with modest grid connection). And you don't need fancy vaporware batteries, any type will do, since they stay on the ground.