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 .