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

On Mar 17, 7:45*pm, wrote:
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

Tension controlled winches are certainly safer and provide higher
launches than speed controlled ones - any winch with an automatic
transmission is speed controlled since that's what the automotive
drive train was designed to do.

I'm not sure I follow the rest of your post. Hopefully an English
translation will be available.

Bill Daniels

The article says that the older gasoline powered winches with
automatic transmissions are tension controlled types, or at least
allow themselves to be controlled that way. I'm not familiar with
transmissions to know either way, just citing what the article says.

They go on to recommend that the existing electric ones and the
Diesels commonly used at least install a tension meter. Further, the
older Hercules winches should be abandoned as they are not up to par,
break down often and are not of the highest standard. These are mainly
from eastern Europe.

To take away, besides maintaining the equipment, is to realize that an
avoidable danger is in accelerating too fast in the first few seconds,
because this can (emphasis on "can") cause an unavoidable pitch up
movement that can not be compensated for with the available elevator
authority - resulting in either a high speed and nose high stall at
low altitude due to an excessive angle of attack or a rope break (weak
link). the former is almost always fatal. The latter not, but can be
if the pilot does not react properly and can contribute to
accidents.

At 03:26 18 March 2009, bildan wrote:


Tension controlled winches are certainly safer and provide higher
launches than speed controlled ones - any winch with an automatic
transmission is speed controlled since that's what the automotive
drive train was designed to do.

I'm not sure I follow the rest of your post. Hopefully an English
translation will be available.

Short of fitting a speed controlling governor, I don't think that any
current winches are 'speed controlled'. Some earlier diesel powered
winches did have this arrangement, but it was found not to work. During a
properly controlled winch launch the motor and drum speeds reach a maximum
as the glider lifts off, and then decrease during the rest of the launch,
due to vector effects and wind gradients.

Winches with automatic transmissions , such as the Tost and the Skylaunch,
will give perfect good constant pull/tension launches as long as you use an
appropriate throttle or power setting. The Tost depends on the skill of the
driver to do this, but the Skylaunch has an adjustable throttle stop that
you can pre-program according to the glider type and headwind.

Derek Copeland

The article is especially critical of the electric winches that they
say are only speed controlled. They said they tried to talk to the
manufacturer (in Germany), but they refused to discuss the issue. They
also mention hydro winches some of which have the same set up - only
speed controlled - at least that's how I understood the article - and
some Diesels. Though they mention that some set ups do have both a
speed and tension indicators - sort of a hybrid.

It is clear that they implied that gasoline driven winches with
automatic transmissions, which are widespread, are the safest ones and
explain the theory as to why, namely because they are tension
controlled. I'm just the messenger.................

I remember reading about winches with torque converters, I think the
Tosts - which is a component of the automatic transmission, so not
speed controlled, but torque regulated via the transmission =
controlling tension on the cable, not the drum or cable speed.

Point is, primarily speed controlled or regulated winches are the most
dangerous type in the statistics table they produced in the article.

One final point from the article:

Only the winch operator/winch can ensure that the first seconds of the
launch are not in the red zone. The pilot can do absolutely nothing if
the winch catapults the glider into the air in a manner that exceeds
the elevator authority and the maximum angle of attack is exceeded at
50 feet in 2 seconds or less. If that happens, rare as it has
occurred, it has always been fatal. A tension controlled winch would
not do this..........ditto if the launch is too strong, causing a rope
break or weak link break............

Interesting. In the UK the accident statistics confirm that there are more
serious injuries/fatalities/damaged gliders per 100000 launches by winch
than by aerotow!

Automatic transmissions would provide constant torque rather than tension
or speed. And then only at a fixed throttle setting.

The predominant accidents with winches are 1) wing drop during ground run;
pilots must release before the wing touches the ground 2) stall during
rotation, it is hard to know whether these are elected rotation or
automatic rotation 3) power loss below 100' and inappropriate pilot
response and 4) power loss mid launch.

Mechanical or electrical devices to maintain torque, speed or tension are
all very well in their place but there is no unique solution as different
conditions apply at different parts of the launch. There is no substitute
for pilot and winch driver training and awareness.

I recommend that all UK pilots read the annual BGA report on glider
accidents and that they promote the training initiatives from the BGA
which appear to be reducing the number of accident and incidents in our
sport.
Best wishes

JohnR-K

On Wed, 18 Mar 2009 10:15:07 +0000, John Roche-Kelly wrote:

2) stall during rotation, it is hard to know whether these are
elected rotation or automatic rotation

Note to any Libelle drivers out there who are thinking of trying winch
launching for the first time.

Libelles winch well provided the pilot has been given a proper briefing
by somebody who is familiar with winch launching them. However, with
incorrect technique they can snap-rotate at lift-off. There is nothing in
the owners manual about this.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

If you don't have a modern tension-controlled winch you can still get a safe
launch by using the "poor mans" tension control as we do with our 650HP,
supercharged Chevrolet Suburban auto tows. We brief the driver on the
airspeed range we want and then during the launch the pilot holds down the
mic button and continuously transmits the indicated airspeed. It works
great and enhances safety.

Karl Striedieck

wrote in message
...
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

On Mar 17, 11:12*pm, wrote:
The article says that the older gasoline powered winches with
automatic transmissions are tension controlled types, or at least
allow themselves to be controlled that way. I'm not familiar with
transmissions to know either way, just citing what the article says.

They go on to recommend that the existing electric ones and the
Diesels commonly used at least install a tension meter. Further, the
older Hercules winches should be abandoned as they are not up to par,
break down often and are not of the highest standard. These are mainly
from eastern Europe.

To take away, besides maintaining the equipment, is to realize that an
avoidable danger is in accelerating too fast in the first few seconds,
because this can (emphasis on "can") cause an unavoidable pitch up
movement that can not be compensated for with the available elevator
authority - resulting in either a high speed and nose high stall at
low altitude due to an excessive angle of attack or a rope break (weak
link). the former is almost always fatal. The latter not, but can be
if the pilot does not react properly and can contribute to
accidents.

The pleasing part is that the new German statistics show winch launch
actually safer than air tow. I've always felt that this should be the
case if the equipment was well maintained and the pilots were trained
to the same level as is common with air tow.

However there seems to be a lot of technical confusion in the article.

"Tension Controlled" means that rope tension is continuously monitored
and controlled through an automatic feedback loop. There are very few
winches that do this. Two American built super winches are both
tension controlled with feedback systems.

Automatic transmissions are designed to help a vehicle driver maintain
highway speed on varying road grades - that's speed control and the
exact opposite of tension control. There is no torque regulation in
an automatic transmission and there is no way to modify one to provide
it. To refer to them as "tension controlled is plain wrong.
Automatic transmissions taken from road vehicles simply don't belong
in glider winches.

Electric winches could easily be tension controlled by just monitoring
the current flowing to the motor as could hydrostatic winches by
monitoring hydraulic pressure although a running line tensiometer
would be a better solution. My understanding is that the ESW-2B is
tension controlled. I know for a fact that both American super
winches under development ARE tension controlled.

Specific attacks on electric winches show a complete lack of
understanding of electric power. The innate characteristics of
electric motors make them ideal for torque control.

"Older gasoline powered winches" most likely mean underpowered winches
that are actually "tension limited" such that the glider pilot can
control airspeed with pitch. To refer to these as tension controlled
is unwarranted and will confuse the issue. These are not "tension
controlled".

The hysterics about initial acceleration needs hard data not theory or
speculation to back it up. The experiments I have done with "pitch
strings" used as an angle of attack indicator suggest that the AOA is
nowhere near stall regardless of initial acceleration. In fact,
greater acceleration actually reduces peak AOA.

The preceding paragraph needs to be qualified by saying there are a
small number of types with well deserved reputations for
uncontrollable pitch-up under hard acceleration. There are relatively
few of these and they are .