On Mar 18, 11:39*pm, wrote:
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.

I didn't accuse anyone of "hoky-poky" and certainly not the publishers
of Aerokurier. I just said that statistics don't work very well for
accident analysis since the data set is too small to draw meaningful
conclusions. To the extent that you analyze anything with accident
statistics, it's pilot skill. That dominates the results not
equipment or procedures. Inconsistent and variable pilot skills
introduces way too much "noise" in the data. Statistics are simply
the wrong tool.

The right tool for this problem is engineering. Every single
parameter can be analyzed with measurement data. If excessive
acceleration does, in fact, reduce AOA margin, that would be very
straight forward to measure. Just install an AOA indicator,
commercial units are available, and simultaneously measure
acceleration with a tensiometer or with a simple video camera. Start
slow and work up. If the stall margin is getting smaller, you'll know
when to stop. Rock solid engineering data will also validate
mathematical models - or not.

I happen to think that the "Kavalierstart" you speak of is pure pilot
error. The pilot causes, or allows, the glider to rotate into a steep
climb before he has safe airspeed. Once over-rotated and stalled,
there is insufficient elevator authority to reverse the situation -
he's riding a kite not flying a glider. A good pilot can prevent this
at accelerations right up to the breaking strength of the weak link.
I know because I've done it.

Requite qualification: There MAY be a very small number of gliders
whose inertially induced pitch-up under hard acceleration exceeds the
elevator authority to prevent it. .