On Mar 22, 4:00*am, Del C wrote:
As far I can find out, Bill has only done a few hundred launches on rather
underpowered and overgeared old US Gehrlein type winches, plus a couple of
launches on his 'US Superwinch' in a Grob G103 before the drum was
crushed by the synthetic cable, something else I warned him about! The
G103, being low winged and quite heavy, is not prone to over-rotation
accidents anyway, as identified in the Aerokourier report.

I have personally witnessed several vastly overpowered launches involving
K6 and K8 gliders, and have sat through 3 myself, in a K8, a Standard
Cirrus and a DG101. They really do go into a near vertical climb, often
despite the best efforts of the pilot to control the rotation.
Particularly in the DG case I was lucky not to join the accidents
statistics, as I slipped back up the seat as the glider rotated and was
only able to keep the stick just off the backstop with my fingertips.

Just about everyone in Europe, where we we have a lot of winch launching
experience, disagrees with Bill's views. As to engineering data, I have
seen none whatsoever from Bill, whereas I have supplied quite a lot plus
illustrative videos on the Yahoo Winch Design Group. *

If you know the position of the belly hook and the centres of gravity and
pressure in a given glider, it should be possible to calculate the
rotational couple for various levels of pull, and at what level it will
overpower the elevator.

Derek Copeland

At 01:24 22 March 2009, bildan wrote:

On Mar 20, 7:00=A0am, Derek Copeland *wrote:
As I have tried to explain to Bill on numerous occasions, and on
various
forums, the uncontrollable over-rotation you get from an over-powered
winch launch is caused by the pull line to the belly hook being below
the
glider's centre of gravity and centre of pressure. This causes a
rotation
for mechanical rather than aerodynamic control reasons. This is why
high
winged gliders, such as the K6 and K8 are most at risk.

If you get such a launch, even holding the stick hard forward all the
tim=
e
from 'take up slack' will not prevent the over-rotation, although it
might slightly reduce your chances of instant death from a flick spin.

Such events can be easily avoided by by controlling the winch so that
the
ground run acceleration is not more than about 1.0g (or less for the
type=
s
mentioned above). This will still get you airborne and climbing within
about 3-4 seconds, which most pilots find quite fast enough! It will
also
make very little difference to the achieved height.

Derek Copeland

At 22:41 19 March 2009, bildan wrote:

As the glider leaves the ground, the inertial rotation will begin but
if the acceleration continues, the elevator effectiveness will also
continue to increase with the square of the airspeed. =A0Rotation
can't
happen instantly because the glider has mass and rotational inertia.
In fact, the pilot has to start backing off the down elevator to
allow
the glider to rotate into the climb.

Now, contrast this with a slow acceleration. =A0The glider staggers
into
the air and the nose-up inertial couple starts the rotation but the
low speed and acceleration doesn't provide adequate control. =A0The
nose
rises as the pilot struggles to control it with inadequate
airspeed.....

I've collected stories on this type of accident for decades and they
ALWAYS happen with slow acceleration.

And just as often I've challenged you to produce ANY engineering data
to support your mere opinion. *You have not and I believe you cannot.

Derek, I have more experience with ground launch than you are likely
to achieve in your lifetime.

No, Derek, Only YOU disagree. All you are doing is "Bible Pounding"
hoping that by repeating the same thing over and over ever more loudly
people will accept it on faith. I think people are smart enough to
demand proof. I accept nothing on faith. I want engineering
measurements to support each and every detail.

Furthermore you are the sales representative for a particularly bad
winch design seeking to discredit all other approaches any way you
can. If you aren't being paid for this, you should demand to be.