Winch Launch Safety Study

Martin Gregorie wrote:
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.


The same is true for the Ka8. I haven't winched one for some time, but
still have the scars where my knuckles would hit the instrument panel
even on a normal speed launch start!

Karl,
that airspeed communication on a winch would work well on the latter
part of a winch launch, but not for the first dew seconds, which is
the most dangerous part, if the winch driver applies too much power at
the outset. I'm just doing the best I can in translating the technical
terms. When they talk about tension controlled winches the word they
use is "Laststeurung" for speed controlled, they use the term:
"Drehzahlregelung" (OK better translation would be RPM controlled).

Bill,
They devote almost an entire page to explaining that the Electric
winch (they don't name it, but it's obviously the E2B) is indeed RPM
controlled in the initial launch phase and they tried to talk to the
manufacturer. The accident statistics are published in the article
with charts and graphs and it's clear as day that the first few
seconds of the launch are the most critical and require the most care
and that winches which are RPM controlled are involved in more
accidents in exactly this phase of the launch by a factor of 7. It's
not even close. Diesel powered RPM controlled winches are involved in
more accidents in this phase by a factor of 2.5 than tension
controlled ones - the latter of which are the vast majority operated
in Germany.

I'm not a transmission expert, so I do not know if certain
transmissions can be operated to hold a certain torque or cable
tension or not. The article does not get into the intricacies of
transmissions, but it does go into how the electric winch functions,
which is too lengthy and technical for me to translate here. The end
result is that it functions as an RPM controlled winch. They also
mention electric winches could be built to be tension controlled,
apparently the E-2B is not.

If you freeze the gas pedal on a GM SUV in flat terrain, you'll
maintain a steady speed. But then, if you start going up hill, you'll
slow down if the gas position is maintained as before and not
increased. It seems to me, the transmission does not maintain a
constant speed of the SUV or RPM of the wheels at the same power
setting, rather it is a torque converter from engine to wheels and
maintains constant torque to the wheels at a constant power setting -
regardless of wheel RPM (vehicle speed).

Two points Bill,

1) Why do you think that automatic transmissions in vehicles (or winches)
try to maintain a constant speed? If you come to a hill and keep the
throttle setting the same, the vehicle will slow down! As a glider rotates
into the full climb and demands more power, the winch cable will also slow
down if you maintain the same throttle setting. Are you sure you are not
getting confused with cruise control?

2) Obviously you have never watched a dangerously steep, overpowered,
over-rotation on a winch launch. I have!

Generally these involve lighter, high wing gliders such as K6s, K7s and
K8s. Usually they go into a near vertical climb, often despite the pilot
holding the stick on the forward stop, followed by a weak link failure. On
one occasion a K8 got into such a steep climb that the belly hook just back
released, due to the extreme angle between the fuselage and the cable.
These events normally leave the glider pointing almost vertically at the
sky at about 100ft with no further means of propulsion! Fortunately at our
club, none of these glider flicked, and were being flown by youngish,
switched on pilots who managed to get them down safety. I dread to think
what would have happened if a numpty had been flying them.

I know a lady who was almost knocked unconcious during at the start of a
very overpowered winch launch, when she banged her head very hard on the
canopy frame of her K6. Also there have been a couple of fatal flick spin
accidents in the UK where it is believed that the pilots slipped back in
their seats and pulled the stick hard back as a result. These were both in
glass single seaters with rather reclining seatpans.

There is no case for exceeding about 0.8g acceleration during the ground
run. This gets you up to flying speed in about 3 to 4 seconds. Most pilots
find this enough!

Derek Copeland



At 15:16 18 March 2009, bildan wrote:
.

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 .

On the other end of the scale, only 8.7% of the accidents with winch
launches involves a wing drop to the ground.

On Mar 18, 11:44*am, wrote:
Karl,
that airspeed communication on a winch would work well on the latter
part of a winch launch, but not for the first dew seconds, which is
the most dangerous part, if the winch driver applies too much power at
the outset. I'm just doing the best I can in translating the technical
terms. When they talk about tension controlled winches the word they
use is "Laststeurung" for speed controlled, they use the term:
"Drehzahlregelung" (OK better translation would be RPM controlled).

Bill,
They devote almost an entire page to explaining that the Electric
winch (they don't name it, but it's obviously the E2B) is indeed RPM
controlled in the initial launch phase and they tried to talk to the
manufacturer. The accident statistics are published in the article
with charts and graphs and it's clear as day that the first few
seconds of the launch are the most critical and require the most care
and that winches which are RPM controlled are involved in more
accidents in exactly this phase of the launch by a factor of 7. It's
not even close. Diesel powered RPM controlled winches are involved in
more accidents in this phase by a factor of 2.5 than tension
controlled ones - the latter of which are the vast majority operated
in Germany.

I agree that the first few seconds are the most critical but there's
nothing here that suggests a rigorous understanding of what exactly
happens in those seconds. Statistics are nearly useless since the
sample is WAY too small for meaningful answers. In any event, the
proximate cause of 99% of all glider accidents is random pilot error
which is not amenable to statistical analysis.

What is needed, and the Germans are extremely good at this, is a full
technical investigation with fully instrumented gliders and winches.
We need actual tension, airspeed and AOA measurements. A few days of
high quality engineering measurement is worth millions of words of
speculation, opinion or statistics. Unfortunately, the mere mention
of winch launch seems to bring out huge amounts of speculation and
opinion.

Tension controlled means that there is a means of directly measuring
tension real time and a means to control it - preferably automatically
with a feedback loop. I have spent 10 years studying winch design and
I believe there are very few such tension controlled winches in
existence. This is most likely a translation problem.


I'm not a transmission expert, so I do not know if certain
transmissions can be operated to hold a certain torque or cable
tension or not. The article does not get into the intricacies of
transmissions, but it does go into how the electric winch functions,
which is too lengthy and technical for me to translate here. The end
result is that it functions as an RPM controlled winch. They also
mention electric winches could be built to be tension controlled,
apparently the E-2B is not.

I do not believe this is acutally the case although the article may
say it.


If you freeze the gas pedal on a GM SUV in flat terrain, you'll
maintain a steady speed. But then, if you start going up hill, you'll
slow down if the gas position is maintained as before and not
increased. It seems to me, the transmission does not maintain a
constant speed of the SUV or RPM of the wheels at the same power
setting, rather it is a torque converter from engine to wheels and
maintains constant torque to the wheels at a constant power setting -
regardless of wheel RPM (vehicle speed).

True, but an automatic transmission ASSISTS the driver in maintaining
speed on a hill by downshifting and allowing the torque converter to
slip thus multiplying torque at the wheels.

Here's where this goes wrong in a glider winch. The air is never
still, and being glider pilots, we want to launch into thermic
conditions. If the winch is equipped with an automatic transmission
salvaged from a road vehicle, and the glider encounters a thermal
during the launch, the transmission will see this as increased load
just like a hill and increase torque and therefore increasing rope
tension. In effect, pulling the glider down through the thermal
causing an airspeed spike - the exact opposite of what you want which
is to reduce rope tension letting the glider climb in the thermal.

Conversely, if the glider encounters sink, the automatic transmission
will REDUCE torque and therefore tension - again the exact opposite of
what you want which is to increase tension helping the pilot maintain
safe airspeed.

Further, if the pilot tries to reduce excessive airspeed by increasing
pitch, the transmission will see this as increased load and ramp up
tension frustrating the pilot. If the pilot lowers the nose in an
effort to increase airspeed, the transmission will decrease tension
again frustrating the pilots efforts to control airspeed.

Automatic transmissions are marvelous devices when used in road
vehicles but they are grossly misapplied when used in a glider winch.
It introduces a "wild card" that neither the winch operator nor the
pilot can predict or control.

US winch designers are using hydrostatic or electric drive with active
tension control to provide exactly the correct rope tension on every
launch regardless of atmospherics, glider type or pilot technique.
This is FAR safer than older winch designs.

Bill Daniels

I agree that the first part of a launch that might involve excessive
acceleration and subsequent uncontrollable over rotation would not be safer
with our continuous airspeed transmission procedure. Things get out of
control way too fast for any radio transmission to help. The radio comes
into play after the glider is climbing out and the airspeed is within the
range the pilot requested.

Also, auto launches generally can't put as much horsepower into the glider
as a winch, and thus the chances of over rotation with the stick full
forward are not as great. However, it happened to me once when my ASW-17 was
being launched by a 180 HP Jeep. It was scary to have the stick full forward
and be pointed up too steep near the ground. But this time the weak link
held and the Jeep didn't stumble, so it worked OK (and made a believer out
of me!).

Karl Striedieck


wrote in message
...
Karl,
that airspeed communication on a winch would work well on the latter
part of a winch launch, but not for the first dew seconds, which is
the most dangerous part, if the winch driver applies too much power at
the outset. I'm just doing the best I can in translating the technical
terms. When they talk about tension controlled winches the word they
use is "Laststeurung" for speed controlled, they use the term:
"Drehzahlregelung" (OK better translation would be RPM controlled).

Bill,
They devote almost an entire page to explaining that the Electric
winch (they don't name it, but it's obviously the E2B) is indeed RPM
controlled in the initial launch phase and they tried to talk to the
manufacturer. The accident statistics are published in the article
with charts and graphs and it's clear as day that the first few
seconds of the launch are the most critical and require the most care
and that winches which are RPM controlled are involved in more
accidents in exactly this phase of the launch by a factor of 7. It's
not even close. Diesel powered RPM controlled winches are involved in
more accidents in this phase by a factor of 2.5 than tension
controlled ones - the latter of which are the vast majority operated
in Germany.

I'm not a transmission expert, so I do not know if certain
transmissions can be operated to hold a certain torque or cable
tension or not. The article does not get into the intricacies of
transmissions, but it does go into how the electric winch functions,
which is too lengthy and technical for me to translate here. The end
result is that it functions as an RPM controlled winch. They also
mention electric winches could be built to be tension controlled,
apparently the E-2B is not.

If you freeze the gas pedal on a GM SUV in flat terrain, you'll
maintain a steady speed. But then, if you start going up hill, you'll
slow down if the gas position is maintained as before and not
increased. It seems to me, the transmission does not maintain a
constant speed of the SUV or RPM of the wheels at the same power
setting, rather it is a torque converter from engine to wheels and
maintains constant torque to the wheels at a constant power setting -
regardless of wheel RPM (vehicle speed).

Interestingly, my vehicle (VW 6 speed) has an amazing automatic with full electronic control. I now believe such a modern automatic would pass power between engine and spool despite my previos limits of winch design left only to full electric or hydraulic (both with tension feedback).

The current crop of automatic gearboxes could be controlled by an economical PLC (sub $500) and loadcell feedback. Rope speed control is into the 3d PLC graph as well, with wind and ambeint temperature. These gearboxes stay in the gear electronically selected, regardless, and I believe they could be used without a torque converter although I am open to suggestion that this would be an advantage.

A wrecked V10 Diesel Touareg drivetrain from VW is the perfect winch option.

This drive will give the winch operator a simple "EB28" or "libelle" or even better, "tail registration number" input into the winch then hit the go button. His only other input into the launch is an emergency stop or emergency manual override.

The winch PLC (Computer) then confirms the registration is of the glider type memorised (safety feedback from the operator) and automatically selects the correct torque/speed curve to launch that glider. Off it goes, same every launch.

The winch operator can then download the data daily on a memory stick and invoice the pilot for the launch with full information -hieght, time, windspeed, temp, etc.
Should the pilot advise the launch needed a different parameter, this can be uploaded for his next launch.

Over time this data may be on servers world wide and the known safety margins set. Should the pilot be requesting a curve outside this window of safety he could be appraised of a possible issue with his launch technique or his glider airworthiness!

There is no way this safe, reliable launch can be acheived with the outdated drives of a 18th century automatic transmission, period.

They may have been up to the job, sure, but if you are to build a new one, dont start backwards!

Plenty to read at the yahoo winch design group
http://groups.yahoo.com/group/winchdesign/

bagger

On Mar 18, 12:30*pm, Derek Copeland wrote:

2) Obviously you have never watched a dangerously steep, overpowered,
over-rotation on a winch launch. I have!

No, I haven't seen any of the weird things you describe. They all
seem to happen in your immediate vicinity. I wonder why.

At 23:53 18 March 2009, bildan wrote:
On Mar 18, 12:30=A0pm, Derek Copeland wrote:

2) Obviously you have never watched a dangerously steep, overpowered,
over-rotation on a winch launch. I have!

No, I haven't seen any of the weird things you describe. They all
seem to happen in your immediate vicinity. I wonder why.

Probably because I'm a gliding instructor at a large and very busy club
that does a lot of winch launching. I also visit other clubs that winch
launch.

I should add that probably 99% of winch launches go to plan (including
deliberate practice launch failures by instructors) without any
difficulties. About 1% suffer cable or weak link breaks, or other
technical failures of one sort or another. Given proper training these
should be just an inconvenience, rather than an emergency situation.

Once it was recognised that over powered winch launches were a problem for
lighter gliders, we reduced the power settings used for these types and
opened the winch engine throttles a bit more slowly. I haven't seen a
'rocket launch' for quite a few years now.

Derek Copeland

Karl,
I agree that vehicles are not prone to make gliders do space shuttle
like launches, due to all the inertia of that set up. Though thanks
for sharing that even there it is possible, not just with winches.

Bill,
The articles has an emphasis on heavy analysis that I am not going to
translate now, nor do I even have permission from Aerokurier to do
that. It's not my article. But trust me, it is very thorough and they
also calculated different scenarios. When there is and accident with
heavy damage or a fatality, the cause is investigated thoroughly and
that cause is listed in the tables in the article. There is no
statistical hoky poky. What for?

I would not presume to start with the assumption that the statistics
are somehow skewed, wrong, massaged or manipulated. If you want to
blast off on winch launch full power from zero on a 300HP (or more)
winch, vastly exceeding 1g and doing a space shuttle launch
simulation, that's your business. The analysis clearly shows that
doing that is 2.5-7 times more dangerous than accelerating under 1g
for the first few seconds. After that, the article says that tension
and airspeed can be higher than is the norm today with no problem,
provided a weak link is used that can handle it.

When I have some time, I'll post at least the accident tables and the
winch accident rate comparisons by winch type. It's easier to see what
I'm saying with the tables in front of you, rather than just my choppy
interpretation and translation of th text. It's very technical.

Speaking of experiences, flying all manner of gliders in Germany and
having participated and watched thousands of winch launches myself -
I've seen and participated in my fair share of space shuttle launches
"Kavalierstart", even with the stick full forward. Unlike Karl, I was
young and not so smart and I wasn't scared at all the few times it
happened to me and we criticized pilots when we saw it happen to them
(like they did it on purpose...free beer). Though I knew it wasn't
right and battled the nose down as soon as I could, there is nothing I
could do about it. That it was dangerous I knew, but I was thrilled to
be blasting off like that since it happened so fast and there was
nothing I could do about it anyway but push the stick full forward.

Simply put, if the rope tension in the first few seconds exceeds 1g
rope tension (not aircraft mass acceleration), the pilot is like a
passenger and can do nothing to correct the situation while the AOA is
pushed to the limit or much closer to the limit. Hopefully, the AOA is
not exceeded for any reason, that is the wing does not stall, because
if it does, the outcome is certain death within the first 7 seconds or
so.

Please understand that the 0.5g-1g tension is measured as rope tension
and not as felt inside the glider as mass acceleration. If you have a
strong head wind, it doesn't take much initial speed or mass
acceleration to create a space shuttle simulation (perhaps that's what
happened to Karl) as the maximum rope tension will occur at a much
slower drum (car) speed and set in much quicker than with no wind.
That is why tension controlled winches are safer as they easily
compensate for this - they deliver a certain rope tension and that's
it, regardless of wind and the drum speed will vary on it's own. It's
like the car rolling up hill - the tension will be the same, only
it'll roll slower up the hill and faster down or flat. RPM winches do
not compensate for any of this. On climb out it's fine, but not in the
first few seconds.