Winch Launch Safety Study

"This discussion always gets the "Safety Nazis" wringing their hands
and wailing every time. ( But never, ever, producing any hard data.)
"

Bill, for once, please, answer the simple question:

What the initial tension, measured in G that you consider ideal on
initial launch? Are you afraid to answer this question that I am now
asking of you for the third time already? You can't complain about
others not providing data (which is not true) if you refuse to even
begin to do so yourself. So put up already.

Can I add that after a very sucessful 6 month trial with a loaned
secondhand Skylaunch winch, Lasham Gliding Society has ordered 2 new ones
that will be arriving shortly.

Lasham is the largest and probably most professional gliding club in the
UK, so its Committee and Management would not have not have entered into
this major financial investment lightly or without considering the
alternatives. I am not a member of the Management or the Committee by the
way.

Can I further add that this winch will smoothly launch anything from
lightweight little vintage single seaters up to big and heavy DG1000Ts,
Duo Discus turbos, and ASH25 turbos. As John says below, the automatic
gearbox changes up into top very early during the ground run and normally
stays there for the rest of the launch. The gearchanges are imperceptable
to the pilot and we have not found a problem with weak links breaking
during the ground run, or at any other stage of the launch for that
matter.

Derek Copeland

P.S. I still want to know how many winch launches Bill Daniels has
actually taken? He demands exact data from others, but won't give out any
himself!

At 00:15 26 March 2009, John Galloway wrote:
At 16:43 25 March 2009, bildan wrote:

Everyone has experienced the imprecise surging when backing a car with
an automatic transmission to align a tow ball with a trailer hitch.
Imagine trying to control the acceleration a 1000 pound glider with a
drive train intended for a 6000 pound road vehicle.

Anyone who thinks any of this is not true, needs to produce some valid
measurements to the contrary. I believe validated data.

Bill,

I have been involved in a lot of discussion a debate here in Scotland
abut
the merits or otherwise of Skylaunch winches and I have been launched by
one and have launched about 8 gliders with one. As you well know
because
you have been told this on another forum the auto box is a complete
non-issue. It changes into third during the ground run and stays in
fixed
ratio top gear throughout the launch - only exeptionally changing down
under very heavy loading during the main part of the launch. The early
upwards gear changes are undetectable to the glider pilot.

I don't know what you consider to be validated data if not 40 odd
winches
over many years of use without problems with controllability related to
the
auto box. I can understand your wish to promote the merits of tension
controlled winches but to do so by denigrating a clearly successful
alternative design reveals more about your mindset than the winch in
question. It is a shame that you have no practical experience of the
Skylaunch which in our club trials worked equally successfully for K8s
to
Duo Disci

I am pretty sure that the long term future of winching will rest with
much
more complex designs but there is none currently available that is
proven
by experience in terms of time of use and numbers built. The Hydrostart
is certainly not yet convincing and is very expensive and, correct me if
I
am wrong, the US version is not launching yet. Considering the cost of
winches, and the fact that once a club becomes winch orientated then
proven reliabilty is critical, then I would reckon that it will be 5-10
years before it becomes wise to risk the purchase of what is now an
experimental winch design. That is not to say that the the US tension
controlled winch will not be successful from the start - just that it is
better to let others act as the early adopters.

John Galloway

To get the absolute maximum acceleration possible for a glider, just
divide a gliders flying weight into its specified weak link strength.
(Tost weak links are now calibrated to +or- 5%) That value is always
around 1.2G - if you don't believe it, read your manual.


Hmmm... Must really go and check the manuals. Or my maths.

IIRC mine (a newer AS model) says 750 or 800daN allowable, my flying
weight is normally around 390kg. So that's close to 2g.
We use 1000daN weak links for the ASK21 (empty 360kg according to AS
homepage), so with two occupants around 540kg. That's also around
1.9g!

Regards
Marcel Dünner

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

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

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

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

A Yahoo groups forum on Glider Winch engineering. Some posts review tension
control, ?? .......
http://dir.groups.yahoo.com/group/wi...eer/message/36
http://dir.groups.yahoo.com/group/wi...eer/message/38

and even one thinking about using battery power?
http://dir.groups.yahoo.com/group/wi...eer/message/40
Did anyone get a electric battery launch before?

David.


At 08:30 28 March 2009, Derek Copeland wrote:
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