Winch Launch Safety Study

In the recent Aerokurier, there is a very good 2 part article on winch
safety, which I think everyone should read who is interested in winch
launches. I read it in the hard cover version in German, so I don't
know if an online version is available.

The main takeaways for me are the following statistics:

- Winch launches are the safest launch type
- Tension controlled winches are far safer than speed controlled ones,
such as the new electric, hydro and diesel designs. They recommend
modifying them to tension controlled ones, as the data is clear.
- initial tension at he beginning of the launch should be about
between 0.5g and 1g - depending on type.
- At the beginning of the launch, there is a danger that if the
acceleration is too strong, it could exceed the elevator authority of
gliders to stay in a safe angle of attack. A high speed (or in the
case of a rope break) low speed stall could occur - which are almost
always fatal in this phase. Plenty of evidence of this is features in
the article, including the fact that GROB models are never involved in
this type of accident because of their large elevators and low mounted
wings, generally limiting pitch up forces.
- Permissible tension forces, tow speeds the weak links should be
changed to allow for faster tows (though not in the beginning phase) -
Especially in the case of GROB models as the weak link used for GROBs
are too weak as seen in those often breaking and those models often
involved in accidents involving broken weak links. Stronger ones from
1.6-1.9g should be used for GROBS.

- The biggest causes of accidents during winch launches are :

1. Winch malfunctions
2. Rope Breaks

These two points can be addressed by proper care and maintenance of
the equipment.

And again, speed controlled winch designs, like the newer ones, are
far more accident prone, than tension controlled ones. What is needed
is tension, not constant speed, so the metric being measured is the
wrong one and it is more difficult for the winch operator to adjust
from one model to the next based just on speed.

Also speed controlled winches give the opposite response to pilot
inputs compared to tension controlled winches. On a Speed controlled
winch, pulling will increase airspeed and pushing will decrease it. On
a Tension controlled one, pulling will reduce airspeed, while pushing
will increase it. They both produce opposite results per pilot input.

In the beginning phase of the launch, the tension controlled one has
obvious clear advantages and is far safer statistically. Having said
all this, winch launches are safer than aerotows.

Someone please ask commercial operators stateside to offer winch
launches, please.........like at Llano, Cal City, Minden,
etc.........you can pick up a used Tost winch starting around 7k Euros
- a lot cheaper than rebuilding, insuring and operating a Pawnee.
Tom Vallarino