THE LONG AWAITED BREAK THROUGH IN BATTERY TECHNOLOGY HAS BEEN FOUND

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.


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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.

On Sun, 17 Jun 2018 09:19:33 -0700, moshe.braner wrote:

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.

From experience with Supacat and Skylaunch twin drum winches, the actual
launch takes around 35-40 secs in normal conditions, but then theres a
fair amount of throttle applied to pull the cable down before it drifts
too far, so 1 minute of run-time per launch seems reasonable.

On our field (1000m cable run, twin drum winch) the best launch rate we
ever achieved was 18 an hour - and apart from the winch driver and launch
marshal that required 3-4 extra full-time helpers, i.e. one guy in the
cable truck and at least two extra people retrieving landed gliders,
moving the launch queues up to the twin launch points, AND for no
briefing delays and other fannying about at the head of the queue.

A bunch of us, all recent solos and flying the club's SZD Juniors used to
get stuck in while waiting for a Junior to land, and no matter how we
tried we couldn't top 18 launches an hour. It didn't need much in the way
of long landings, and briefings etc to drop that rate quite a bit.

BTW 5 KW of solar panels is only about $5,000 these days. That would do
about 3 launches per hour.

We routinely do more than that - 100 launches isn't unusual for a decent
day.

And you don't need fancy vaporware batteries, any type
will do, since they stay on the ground.

Agreed - wet lead acid would be fine, particularly as it all helps to
hold the winch down.

However, as I said, we went to other way and have two winches - both are
7-8 litre V-8s running on LPG and using Spectra cables. One is a Skylaunch
and the other is a Tost which was rebuilt by Skylaunch. Since we operate
7 days a week, mostly winched flying from the start of April to the end
of September, we've found that having only one winch loses a bit too much
time on servicing etc, so we got the second one. This lets us alternate
them so the offline one can be serviced etc.


--
Martin | martin at
Gregorie | gregorie dot org

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.

Our winch uses on average 1 cup of gas (~240cc) per launch. The engine is a 7.5l V8 with a carburetor. Going to fuel injection would lower that consumption but we would have to do a lot of launching, before we recover that investment.
There is a very promising electric winch project on the way in the US. Stay tuned for news in the near future...

Uli
'AS'