Winch Launch - Fatal

At 12:09 14 December 2016, Don Johnstone wrote:
At 10:30 14 December 2016, Terry Walsh wrote:
At 09:19 14 December 2016, Jim White wrote:
At 01:59 14 December 2016,
wrote:

Don, you brought up the old pitch-up myth so I'll go there.

Pitch-up on acceleration can only happen with the tailwheel in
the ai
and
=
that can only happen if the glider is slowly dragged into the air
with
feeb=
le acceleration and THEN strong acceleration applied. It can't
happe
if
s=
trong acceleration is applied at the very start of the ground roll
and
main=
tained until the glider reaches the normal airspeed for rotating
int
the
c=
limb.

I could go on at length about this but I wrote a long paper on it
available=
here
https://dl.dropboxusercontent.com/u/...cceleration.pd
Rather
=
than take my word for it, I very strongly suggest the BGA and
other
nationa=
l clubs do their own investigation using tension loggers. What
you will
se=
e may terrify you.


Hi Bill. If you follow URAS you will see that Don, whilst old and
wise
doesn't speak for the UK gliding community.

Hi Bill,

The theory may be correct but I can assure you that a K18
ALWAYS needs th
application of almost full forward stck after lift off to prevent ove
rotation. This is using a powerful V8 winch with about 2 seconds
of groun
roll. Yes the accleration is still happening after lift off. With a
narro
steel drum throttle response is never instantaneous due to inertia
of th
drum, even with the powerful (300 hp+) V8.

I believe there is a solution to this, one which no one will like, but
which would reduce the frequency of the accidents, unfortunately it
may also very expensive and difficult to achieve on existing aircraft
and would result in a reduction in winch launch height. Move the
launch hook forward.



I've picked this one up rather late, and probably like Don, I have many
thousands of winch launches, in vintage gliders, modern gliders, gliders
with compromise hooks, and with C of G hooks, initially on Tost, not
exactly underpowered, and for the last 20 years on Skylaunch, certainly not
underpowered.
To comment on something Bill said, I have analysed quite a few, from 1 sec
logger traces (perhaps not the most accurate way, but all I've got), and
find initial acceleration to be nearer .6g/.7g, rather than 1g. Tost weak
links are approximately 1.3 times auw, so should take 1g , at least when
new.
The problem with the wing going down is I think, that the pilot can be
unaware. A long time ago I had a 19m Jantar, with a compromise well forward
hook, and a loop of cord attached to the release toggle, because you could
not reach it. One day I took a launch, when I got back a few hours later, a
fellow instructor asked if I knew that the wing had gone down, so hard that
everyone at the launch point turned to look. I probably had 1500 hours on
that glider alone, and quite a few hundred launches in it, but hadn't a
clue anything had happened. To me it was a normal launch, and I got away
with it.
I totally agree though that high acceleration is good, the opposite is not.
Again, years ago, probably in the Jantar again, I had a very slow ground
run, but got away. When I got back, I found that a subsequent launch in an
ASW27, had had a wing down accident, substantial damage, fortunately no
injury. Though not there to see it, I always put that down to a slow ground
run like mine.
Most of the early Schleicher gliders, K8, K18, K6, do need a forward stick
position at the start, unlike most others, when neutral is best. The glider
will aviate when ready, it doesn't need encouraging by the pilot.
Winch launching is not inherently dangerous, any more than walking down the
street is dangerous, unless something goes wrong. Not sure without checking
how many are done in the UK each year without incident, but it runs into
hundreds of thousands. Just a very few go wrong.
What I would like to see is a re-think on launch speeds. High speed is
safe, low speed is not. Yet we have ridiculous situations like the Puchacz,
which I think is otherwise the best training glider available, with a
maximum of 59 kts, yet not really safe on a winch launch below 55 kts. This
is a fully aerobatic, inverted flight glider!!!
With the Skylaunch, perhaps others, the throttle stop is set to suit the
wind and the glider. The driver then advances the throttle lever to that
stop over a second or two. I would like to see a completely computerised
system, whereby the wind profile and the glider are selected, and the
driver just presses a button to launch, and all the parameters are built
in, including initial acceleration, surely not that difficult with modern
technology. Obviously there must be a dead man's handle.
Dave