Winch Launch Safety Study

A few points to add to this.

1) The pilot should also be prepared to abandon the launch if a wing drops
during the ground run. In the UK it is recommended that the pilot keeps his
hand on the release knob during the ground run.

2) I always hold the stick in an appropriate setting for the glider type,
generally always forward of centre, and then rest my arm or elbow against
either my thigh or the side of the cockpit. That way I will not
inadvertantly pull the stick back due to the effects of acceleration and
inertia.

3) Always do your straps up as tightly as possible for a winch launch, and
if the rudder pedals are easily adjustable, set them a bit closer than
normal. If you need back cushions, make sure that they are made of a firm
material. Several fatal winch launching accidents in the UK have been
caused by pilots slipping back up the seat, or sinking back into soft foam
cushions, again due to rapid acceleration and inertia. Possibly another
good reason for limiting acceleration rates!

Derek Copeland

At 11:00 27 March 2009, John Roche-Kelly wrote:
I think you may be missing the point here.
The weak link is to protect the glider airframe from exceeding maximum
loading ie towards the top of the launch, with the cable almost vertical
and the wing loading at its maximum. Using these calculations to
determine
the best acceleration at the start of the launch is bad math(s).
The acceleration on the ground should be safe. Too high and the inertia
of
the stick and the pilot's hand will cause backward movement, with
self-evident results. Too slow and aileron authority is not achieved
quickly enough to prevent wing drop and possible cartwheel!
Typically aileron authority is present just below the stall speed so the
acceleration should be sufficient to get to that speed before a wing can
drop, say 2 seconds or so. Now do the math(s) for your glider. Typical
stall speeds are below 35 kt (17 metres per second). This gives an
acceleration of less than 1g which will comfortably be tolerated by any
pilot. If continued the acceleration will have the glider fully flying
and
high enough to begin the rotation into full climb in another second or
two.
Broken weak links at the start of the ground run are generally due to a
snatched All Out. The launch marshal must ensure that there is no slack
in
the cable before giving All Out by waiting for a genuine movement of the
glider. The wing tip holder must move forward with the glider for as
long
as possible. The wing tip holder should abort the launch if he or she
has
to hold the wings level, they should do so naturally or the wing will
drop
on release.

Best wishes

JohnR-K

On 27 Mrz., 12:00, John Roche-Kelly
wrote:
I think you may be missing the point here.
The weak link is to protect the glider airframe from exceeding maximum
loading ie towards the top of the launch, with the cable almost vertical
and the wing loading at its maximum. Using these calculations to determine
the best acceleration at the start of the launch is bad math(s).

Yes, yes, of course. I didn't mean to give the impression I would like
to be accelerated to the limits of the weak link - that would be
quite frightful. But bildan was throwing wrong figures about and
claiming (indirectly) the weak link limits the acceleration to safe
levels.

Marcel

Despite the alleged 'bildan tension spikes' from the automatic gearboxes
fittes to many current winches, in my experience weak link breaks during
the ground run are extremely rare. If you do get a very overpowered
launch, the weak link will normally break towards the end of the rotation
or early in the full climb. The best video example I can find on youtube
is:

http://www.youtube.com/watch?v=jvK1ONl1CqE

This launch was on a diesel powered winch (also favoured by bildan) where
you typically get a rather slow initial ground run acceleration, followed
by a sudden snatch into the air and often a considerable overspeed for
lighter gliders.

The video also shows what happens if you don't lower the nose quickly
enough after a launch failure. The pilot allows the glider to stall, after
which it never regains enough airspeed to round out. The glider (ASW15)
suffered a collapsed undercarriage and other minor damage, and the pilot a
bruised back. Fortunately nothing more serious, as it looks at one point as
if the glider might spin.

Otherwise weak links normally only break near the top of the launch, where
they are doing their job in protecting the airframe.

Derek Copeland


At 16:07 27 March 2009, MaD wrote:
On 27 Mrz., 12:00, John Roche-Kelly
wrote:
I think you may be missing the point here.
The weak link is to protect the glider airframe from exceeding maximum
loading ie towards the top of the launch, with the cable almost
vertical
and the wing loading at its maximum. Using these calculations to
determine
the best acceleration at the start of the launch is bad math(s).

Yes, yes, of course. I didn't mean to give the impression I would like
to be accelerated to the limits of the weak link - that would be
quite frightful. But bildan was throwing wrong figures about and
claiming (indirectly) the weak link limits the acceleration to safe
levels.

Marcel

Also the wing tip runner should hold the wing at the correct height, too
many hold a high wing too low and a low wing too high.


At 11:00 27 March 2009, John Roche-Kelly wrote:
I think you may be missing the point here.
The weak link is to protect the glider airframe from exceeding maximum
loading ie towards the top of the launch, with the cable almost vertical
and the wing loading at its maximum. Using these calculations to
determine
the best acceleration at the start of the launch is bad math(s).
The acceleration on the ground should be safe. Too high and the inertia
of
the stick and the pilot's hand will cause backward movement, with
self-evident results. Too slow and aileron authority is not achieved
quickly enough to prevent wing drop and possible cartwheel!
Typically aileron authority is present just below the stall speed so the
acceleration should be sufficient to get to that speed before a wing can
drop, say 2 seconds or so. Now do the math(s) for your glider. Typical
stall speeds are below 35 kt (17 metres per second). This gives an
acceleration of less than 1g which will comfortably be tolerated by any
pilot. If continued the acceleration will have the glider fully flying
and
high enough to begin the rotation into full climb in another second or
two.
Broken weak links at the start of the ground run are generally due to a
snatched All Out. The launch marshal must ensure that there is no slack
in
the cable before giving All Out by waiting for a genuine movement of the
glider. The wing tip holder must move forward with the glider for as
long
as possible. The wing tip holder should abort the launch if he or she
has
to hold the wings level, they should do so naturally or the wing will
drop
on release.

Best wishes

JohnR-K

"Alan Garside" wrote in message
...
Also the wing tip runner should hold the wing at the correct height, too
many hold a high wing too low and a low wing too high.


At 11:00 27 March 2009, John Roche-Kelly wrote:
I think you may be missing the point here.
The weak link is to protect the glider airframe from exceeding maximum
loading ie towards the top of the launch, with the cable almost vertical
and the wing loading at its maximum. Using these calculations to
determine
the best acceleration at the start of the launch is bad math(s).
The acceleration on the ground should be safe. Too high and the inertia
of
the stick and the pilot's hand will cause backward movement, with
self-evident results. Too slow and aileron authority is not achieved
quickly enough to prevent wing drop and possible cartwheel!
Typically aileron authority is present just below the stall speed so the
acceleration should be sufficient to get to that speed before a wing can
drop, say 2 seconds or so. Now do the math(s) for your glider. Typical
stall speeds are below 35 kt (17 metres per second). This gives an
acceleration of less than 1g which will comfortably be tolerated by any
pilot. If continued the acceleration will have the glider fully flying
and
high enough to begin the rotation into full climb in another second or
two.
Broken weak links at the start of the ground run are generally due to a
snatched All Out. The launch marshal must ensure that there is no slack
in
the cable before giving All Out by waiting for a genuine movement of the
glider. The wing tip holder must move forward with the glider for as
long
as possible. The wing tip holder should abort the launch if he or she
has
to hold the wings level, they should do so naturally or the wing will
drop
on release.

Best wishes

JohnR-K


To the tune of 'Donald whers yoo trooses' (Scottish folk song)

"Let the wing go high let the wing go low"......you get the drift.

JRS