Auto Tow Information

"Mike Schumann" wrote in message
nk.net...
How long of a runway do you need for an effective / safe winch and/or auto
tow launch environment?

Mike Schumann

With the old manually controlled winches and steel wire, 30 - 40% of the
runway is achievable as release height. However, there is something of a
revolution in winch technology going on right now.

The new high power, computer controlled winches using ultra light 'plastic'
UHMWPE 4.5mm cord can get up to 50% of the runway length in zero wind
conditions. Launching into a headwind increases the release height quite a
bit more. So a 5000 foot runway might get you 2500 feet AGL. That's
usually enough to contact soarable lift if there is any to be had.

Bill Daniels

"Mike Schumann" wrote in message
nk.net...
How long of a runway do you need for an effective / safe winch and/or auto
tow launch environment?

Mike Schumann

You also asked about a safe environment.

The glider should always be able to land safely from a launch failure.
That's pretty easy to achieve since the glider will have enough runway to
land straight ahead up to about 400 feet AGL. Above that, a short 360
degree pattern can be flown. The land straight ahead option overlaps
quite a bit with the 360 pattern. The main thing is that a clear area be
available for a glider to land at all times so a pilot dissatisfied with a
launch can just release and land.

I'd like 300 feet of width and a mile or more of length.

Bill Daniels

We used to autotow (straight, and later reverse pulley) from either of
two good surface hard runways at North Weald, Essex, UK. One was 1 ¼
miles long and we only used less that 1 mile of it for the tow car/cable
run (we landed in the undershoot). The other was ¾ mile and we use
almost its whole length. Launch heights were typically about 7-800 feet
in light winds on the shorter run, and 900-1000 feet on the longer run,
for K13's, two-up. With increasing amounts of wind, up to say 15 knots,
we got 1200+ on the short run and 1400 + on the longer run. Highest I
ever got was about 2000; others got higher, in really strong winds.

Going back to launch vehicles, I would say that straight tow with old
bangers is a cheap and viable way, if you have the runway hard surface
and length, for small numbers of launches, and accepting reliability
issues and not the fastest turnaround. With two cables, two launch cars,
and also two cable retrieve cars, you can speed up the launch rate quite
a lot. The technology is fairly simple, relatively easily learned, and
its all cheap. The cable could be the most expensive part of it. The
driving takes a bit of learning to get the technique right, but it's not
too difficult. To save reinventing, it would be best to get some hints
and tips from those who have done it.

My earlier post about the high cost, super spec. truck, was a direct
response to somebody asking for what seemed like that information. It is
a high cost, high reliability, high turnaround solution. Combining it
with reverse pulley also requires appreciable investment in the pulley
system itself too - but a few thousand, compared with lots of thousands
for a new truck. If you don't want the 9,000 launches per year,
professional-style operation that we had that for, and don't want a top
quality system, fine - that's your choice. Those who didn't want to read
about it, tough.

Both reverse pulley systems, and winches, are really specialist design
projects. Amateurs who take them on rarely, if ever, get them right
first time - I have never seen one such. Both Cotswold Club and Essex
Club took several iterations to arrive at their respective designs of
reverse pulley, and ended up with substantial professional workshop
builds.

I have never seen a good first-time-build winch, either. All the good
professional ones I have seen built in the UK came from ex-amateurs who
learnt from several home-grown prototypes and mistakes before
progressing to good, reliable, and high-capital-cost solutions (Supercat
and Skylaunch). I don't know the history of Tost, but there has been a
long tradition of winching in Germany, and the best Tost winches are
also very good. Several Tost-technology winches have been built in the
UK from greater or lesser proportions of Tost kits. The more local
invention to save capital cost, the greater is the risk of the new short
cuts being worse than the well-developed technology, to put it mildly.

When my own club had to cease truck launches at North Weald, and could
not afford new winches for our new grass site at Ridgewell, we bought
four ex-air cadet winches and fitted the best two of them with
replacement high-power engines and automatic transmissions - the first
one by our own amateurs, the other by a professional engineer who had
built a Tost winch previously for his own gliding club. Our ex-ATC
chassis including winch drums and pay-on gear cost about 800 Sterling
each. The conversions cost (very approximately) about 1-2,000 sterling
for the first, using a used ex-tow-truck powertrain; and about 16,000
sterling for the second including a brand new cab and re-engineered
Chevy (I think) engine/trans combination and LPG conversion. ( They are
not perfect, but the bits that are poorest are the original ATC winch
parts and are very difficult to see how to re-engineer. They work
tolerably well, so we live with them. The main problem, when it happens,
is cables snarling up inside the drum/axle mechanism. But that can
happen even on the high cost professional winches - I saw one such
incident at another club last week, and at a different one again today.)

Chris N.




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