On Saturday, March 27, 2021 at 8:47:00 AM UTC-6, AS wrote:
On Saturday, March 27, 2021 at 8:34:29 AM UTC-4, Bob Whelan wrote:
On 3/26/2021 5:13 PM, waremark wrote:
On Friday, 26 March 2021 at 16:25:39 UTC, ProfJ wrote:

It's kind of fun to have all the experts invalidate my actual lived
experience, and also physics. Let's go watch some videos of winch
launches, shall we?

Here's Bruno Vassel launching
https://www.youtube.com/watch?v=VrUT...el=BrunoVassel . Due
to the wonders of actual video evidence, we see the glider taking seven
seconds from first roll to airborne. Here's one from Oxford Gliding -
https://www.youtube.com/watch?v=-eTU...nel=GreatFlyer - nine
seconds from first movement to airborne. Here's one from Mount Beauty -
https://www.youtube.com/watch?v=SE5J...=GeorgeSkarbek -
five seconds to airborne. Here's one - called "Rather fast winch launch"
! - https://www.youtube.com/watch?v=-eTU...nel=GreatFlyer -
five seconds to airborne.

I didn't cherry-pick these, they were the first four I found where you
could see the glider roll. If anyone can find one showing a two-second
roll, go ahead and show us.

Yes, it seems like it's two seconds. That's the problem of sensory
overload. Apparently even the experience of 1500 launches on a variety of
airfields doesn't overcome it.

This one at my club shows the glider in the air after about 2 seconds:

https://www.youtube.com/watch?v=f_ASzIsviAE

Reality is what a person experiences; camera views aren't 100% representative
(cf: Hollywood).

A beady-eyed look at several of the Mt. Beauty launch views-from-afar show
multiple launches with ~2-sec ground rolls *after* the line slack is removed
and the ship is beyond wing-runner assistance...which by my reckoning is "when
the winch launch begins". Everything prior to that is preparation.

YMMV.

Bob W.
Bob - couldn't agree more with your separation between 'preparation' and 'winch launch begins'.
I wanted to point out the Design Guidelines for the design and approval of a glider winch issued by the DAeC in Germany, of which I made a full translation which got 'lost' by the old Yahoo winchdesign group administration when they shut them down:

https://www.daec.de/fileadmin/user_u...2010_Rev02.pdf

Original Text:
Paragraph 2115: Beschleunigungsnachweis
Bei Windstille muss das zu startende Luftfahrzeug nach einer
Beschleunigungsstrecke von 15 m um die Längsachse steuerbar sein und
nach höchstens weiteren 45 m Beschleunigungsstrecke die
Abhebegeschwindigkeit erreicht haben.
Der Roll- und Luftwiderstand, sowie die Seilreibung am Boden müssen
beim rechnerischen Nachweis durch einen Zuschlag von 30%
berücksichtigt werden. Der Zuschlag kann bei der Verwendung von
Kunststoffseilen auf 10% vermindert werden.

Translation:
Acceleration requirements
In clam air, the glider to be launched must have control around the longitudinal axis [i.e. aileron control] after a distance of 15m and must have reached lift-off speed after a further 45m.
Rolling- and air resistance as well as the cable friction against the ground have to be considered in the calculations by a factor of 1.3. This additional friction factor can be reduced to 1.1 when plastic lines are being used.

There are more paragraphs governing the speed and power requirements.
What that means is that any winch designed and built either commercially or by clubs in Germany must comply with these guidelines or else they will not get approved and therefore their operation would be illegal and not covered by by the club's insurance. (The DAeC guidelines are de facto the law, similar to BGA regulations in the UK)
When we (a few winch enthusiasts and I ) started the discussion group winchdesign almost 20 years ago and I provided a full translation of these guidelines (with the written permission of the DAeC), it was the general consensus that having guidelines like this makes perfect sense and avoids most hazardous conditions during the winch launch.

So, if ProfJ sees winches accelerating the gliders in a very anemic way it could mean that either the operator is not doing his/her job correctly or the winch is not designed in accordance with these guidelines, which is very possible since many winches around the world were designed in accordance with the rule 'Hold my beer - watch this!'
But of course issuing strict and heavy-handed guidelines based on sound engineering and physics in the interest of operational safety like these must be just another example of a socialist government stifling individualism and free expression, right? ;-)

Uli
'AS'
Uli,

Appears the file was somehow corrupted either on the server or during the download of the archive. I guess you didn't keep your copy?

Frank Whiteley