Winch Launch Safety Study

On Mar 21, 9:29*pm, wrote:
Bill,
I also wonder if you have considered gusts and turbulence on elevator
authority. The winch RPM speed is not affected by this and will
continue accelerating if that 's what you want, when gusts or
turbulence affect the elevator. Even Tension controlled winches may
not be able to reduce tension quickly enough if this happens. That's
why the initial tension should not be too high to begin with.

RPM is of interest only as far as it is necessary to protect the
engine. It is of no interest in the launch profile. Properly
engineered automatic tension control winches can for all practical
purposes INSTANTLY reduce or increase tension in response to gusts.

I would like to hear your description of how winch settings should be
with some metrics. I know you advocate high initial tow acceleration
launches. But that doesn't really tell me the specifics.

Tension, and therefore acceleration, is limited by the prescribed weak
link strength to no more than about 1.2 G. George Moore has
extensively studied this and shows that a slight tension reduction at
rotation is needed although more actual measurements are needed to
validate that.

On Mar 22, 4:00*am, Del C wrote:
As far I can find out, Bill has only done a few hundred launches on rather
underpowered and overgeared old US Gehrlein type winches, plus a couple of
launches on his 'US Superwinch' in a Grob G103 before the drum was
crushed by the synthetic cable, something else I warned him about! The
G103, being low winged and quite heavy, is not prone to over-rotation
accidents anyway, as identified in the Aerokourier report.

I have personally witnessed several vastly overpowered launches involving
K6 and K8 gliders, and have sat through 3 myself, in a K8, a Standard
Cirrus and a DG101. They really do go into a near vertical climb, often
despite the best efforts of the pilot to control the rotation.
Particularly in the DG case I was lucky not to join the accidents
statistics, as I slipped back up the seat as the glider rotated and was
only able to keep the stick just off the backstop with my fingertips.

Just about everyone in Europe, where we we have a lot of winch launching
experience, disagrees with Bill's views. As to engineering data, I have
seen none whatsoever from Bill, whereas I have supplied quite a lot plus
illustrative videos on the Yahoo Winch Design Group. *

If you know the position of the belly hook and the centres of gravity and
pressure in a given glider, it should be possible to calculate the
rotational couple for various levels of pull, and at what level it will
overpower the elevator.

Derek Copeland

At 01:24 22 March 2009, bildan wrote:

On Mar 20, 7:00=A0am, Derek Copeland *wrote:
As I have tried to explain to Bill on numerous occasions, and on
various
forums, the uncontrollable over-rotation you get from an over-powered
winch launch is caused by the pull line to the belly hook being below
the
glider's centre of gravity and centre of pressure. This causes a
rotation
for mechanical rather than aerodynamic control reasons. This is why
high
winged gliders, such as the K6 and K8 are most at risk.

If you get such a launch, even holding the stick hard forward all the
tim=
e
from 'take up slack' will not prevent the over-rotation, although it
might slightly reduce your chances of instant death from a flick spin.

Such events can be easily avoided by by controlling the winch so that
the
ground run acceleration is not more than about 1.0g (or less for the
type=
s
mentioned above). This will still get you airborne and climbing within
about 3-4 seconds, which most pilots find quite fast enough! It will
also
make very little difference to the achieved height.

Derek Copeland

At 22:41 19 March 2009, bildan wrote:

As the glider leaves the ground, the inertial rotation will begin but
if the acceleration continues, the elevator effectiveness will also
continue to increase with the square of the airspeed. =A0Rotation
can't
happen instantly because the glider has mass and rotational inertia.
In fact, the pilot has to start backing off the down elevator to
allow
the glider to rotate into the climb.

Now, contrast this with a slow acceleration. =A0The glider staggers
into
the air and the nose-up inertial couple starts the rotation but the
low speed and acceleration doesn't provide adequate control. =A0The
nose
rises as the pilot struggles to control it with inadequate
airspeed.....

I've collected stories on this type of accident for decades and they
ALWAYS happen with slow acceleration.

And just as often I've challenged you to produce ANY engineering data
to support your mere opinion. *You have not and I believe you cannot.

Derek, I have more experience with ground launch than you are likely
to achieve in your lifetime.

No, Derek, Only YOU disagree. All you are doing is "Bible Pounding"
hoping that by repeating the same thing over and over ever more loudly
people will accept it on faith. I think people are smart enough to
demand proof. I accept nothing on faith. I want engineering
measurements to support each and every detail.

Furthermore you are the sales representative for a particularly bad
winch design seeking to discredit all other approaches any way you
can. If you aren't being paid for this, you should demand to be.

On Mar 20, 7:00*am, Derek Copeland wrote:
As I have tried to explain to Bill on numerous occasions, and on various
forums, the uncontrollable over-rotation you get from an over-powered
winch launch is caused by the pull line to the belly hook being below the
glider's centre of gravity and centre of pressure. This causes a rotation
for mechanical rather than aerodynamic control reasons. This is why high
winged gliders, such as the K6 and K8 are most at risk.

I understand this exactly and have wrote about it for many years.
Almost all gliders currently in use have no risk at all of
"mechanical" over-rotation. Does a G103 have "Uncontrollable Over-
rotation"?

The "Over powered" launches you speak of are strictly limited by the
weak link to slightly over one G which is a trivial value. Nothing
violent happens at one G unless the pilot initiates it.

At 16:35 24 March 2009, bildan wrote:

Derek, I have more experience with ground launch than you are likely
to achieve in your lifetime.

No, Derek, Only YOU disagree. All you are doing is "Bible Pounding"
hoping that by repeating the same thing over and over ever more loudly
people will accept it on faith. I think people are smart enough to
demand proof. I accept nothing on faith. I want engineering
measurements to support each and every detail.

Furthermore you are the sales representative for a particularly bad
winch design seeking to discredit all other approaches any way you
can. If you aren't being paid for this, you should demand to be.

Bill,

1) So how many winch launches HAVE you done? I have made over 5000 autotow
and winch launches at a number of sites over a 28 year period, both solo
and as an instructor (combined that is).

2) What engineering measurements can you provide? To the best of my
knowledge, nobody has yet found a 100% successful way of measuring winch
cable tension. The cable speeds are too high for Rolling Line
Tensiometers, so this generally has to be derived from torque or throttle
settings.

3) Other than being a satisfied user of Tost and Skylaunch winches, I have
no financial connections to any manufacturer.

Derek Copeland

Bill said:
"... the tension should be the maximum safe value."

OK, let me try this again. Maybe you'll understand this question:

1. In your opinion, what is the maximum safe value expressed in g, for
he initial launch phase?
2. Who else agrees with your position that the initial launch phase
should be aggressive? In this thread alone, nobody agrees with you.
Where are all these people? Mr. George Moore has also said he
advocates a slower launch than you do on the Yahoo groups site.
"Bill has advocated higher ground acceleration rates than I am
generally comfortable with."

I haven't heard a single person support what you advocate. Whatever
you find, please with verifiable quotes.

- And I don't know were your get your sense of what rude is, but
publicly and falsely claiming I am misrepresenting my identity without
any proof on your part what so ever, certainly is rude behavior.

No a Grob G103 is not prone to 'uncontrollable over-rotation' after
lifting off on a winch launch, because it has low set wings, hence a low
centre of gravity, a slightly forward set belly hook, and it's quite
heavy. Depending on the model, it either launches on a relatively weak red
or brown link, so it is prone to weak link failures, as is identified in
the Aerokourier report. So you need to be careful about overpowering it
for a different reason.

However there are many types that are prone to over-rotation, particularly
K6, K7, K8, K13, Standard Cirrus, and many other types of single seater.

In that it is very rare to break a weak link during the ground run,
however violent, it is likely that you can get much faster acceleration
than 1.2g. I think this is because of the fact that the glider is on
wheels and unloads the weak link as it rolls and accelerates forward. If
you where pulling against a concrete block set into the ground, you would
break the weak link every time at the same force. If the weak link does
break as a result of an overpowered launch, it usually does so sometime
during or just after the rotation, which is at the worst possible time! If
you drive a winch (which I do) you can feel the load on the cable increase
as the glider rotates, even if the throttle or tension setting remains
constant.

Have a look at the following video showing a K13 being winch launched:

http://www.youtube.com/watch?v=KUsqw0OwMZA

Note that after a slightly protracted 'take up slack' the tailwheel goes
down onto the ground when the winch driver opens the throttle and stays
there until the glider lifts off, if anything slightly mainwheel first.
This is despite the elevator being held slightly lower than neutral (stick
forward of centre), as it should be. If you have a K13 available, try
sitting two 180lb men plus parachutes in it and then push down down on the
tail until the tailwheel touches the ground. You will find that this
requires quite a lot of force, which illustrates just how powerful the
rotational couple must be.

Derek Copeland


At 16:48 24 March 2009, bildan wrote:
On Mar 20, 7:00=A0am, Derek Copeland wrote:
As I have tried to explain to Bill on numerous occasions, and on
various
forums, the uncontrollable over-rotation you get from an over-powered
winch launch is caused by the pull line to the belly hook being below
the
glider's centre of gravity and centre of pressure. This causes a
rotation
for mechanical rather than aerodynamic control reasons. This is why
high
winged gliders, such as the K6 and K8 are most at risk.

I understand this exactly and have wrote about it for many years.
Almost all gliders currently in use have no risk at all of
"mechanical" over-rotation. Does a G103 have "Uncontrollable Over-
rotation"?

The "Over powered" launches you speak of are strictly limited by the
weak link to slightly over one G which is a trivial value. Nothing
violent happens at one G unless the pilot initiates it.

Originally Posted by

Bill said:
"... the tension should be the maximum safe value."

OK, let me try this again. Maybe you'll understand this question:

1. In your opinion, what is the maximum safe value expressed in g, for
he initial launch phase?
2. Who else agrees with your position that the initial launch phase
should be aggressive? In this thread alone, nobody agrees with you.
Where are all these people? Mr. George Moore has also said he
advocates a slower launch than you do on the Yahoo groups site.
"Bill has advocated higher ground acceleration rates than I am
generally comfortable with."

I haven't heard a single person support what you advocate. Whatever
you find, please with verifiable quotes.

- And I don't know were your get your sense of what rude is, but
publicly and falsely claiming I am misrepresenting my identity without
any proof on your part what so ever, certainly is rude behavior.

I would support a fair bit of what Bill says, which may be why my previos post has been ignored.

Many of our sports members fall into the old dogs and new tricks area, I have a feeling the more experience one has in anything, the more they push against change, especially as we grow older.

I must disagree with Dereks' statement on measuring tension as well, it is a simple thing to do. Perhaps it hasnt been done, sure, but its not hard. (Caveat- I sell loadcells and measurement equipment for a living)

As I have stated, If we can identify we have a problem (we do, people have died) why would we not change? Technology is allowing change, embrace it.
If, with respect of time, we see we were wrong and can change back, what harm? At least we tried.

We can set up winches to do any damn thing we like, every time, regardless of wind gusts, temperature changes, altitute differences, ballast, number of pilots, student requirements, winchperson ability, emergency airspace violations etc, etc. So lets!

If you dis-agree, dont fly off the new winch, simple!


Bagger

In the UK, Holland and Germany about two-thirds of glider launches are done
by winch, so we have a fair bit of experience in this technique. Prior to
about the early 1980s winches were fairly asthmatic things, but the sort
of ideas that Bill is advocating now where tried out as more powerful, big
engined winches such as the Tost and Van Gelder, became available, and
where quickly found to be somewhat dangerous! As the Americans are at last
starting to get into winching, I am just trying to stop them re-inventing a
rather dangerous wheel. All you have to do in reality is to slightly
restrict the power given to those types of glider that can't safely use
it!

Even a fully automated, computerised winch can fall foul of finger trouble
in inputing the launch data, so even there it is best to err slightly on
the size of caution.

Bill has suggested that slowly accelerated launches are more likely to
cause flick spins. That being the case we should have had plenty of these
when we autotowed, where the acceleration is very slow, but we didn't!

If you have a system or a gadget that you can clamp to a winch to directly
measure cable tension, I for one would like to know about it. RLTs seem to
be limited to about 40mph maximum cable speed, which is not enough. The
other approach is to mount a load cell in the glider's hook mount, or at
the glider end of the cable with a radio transmitter to transmit data back
to the winch. The former would be rather expensive for glider owners and
for clubs with a lot of gliders, while the latter would be prone to
breakages when dropped from 2000ft!

Derek Copeland


At 09:59 25 March 2009, bagmaker wrote:

I would support a fair bit of what Bill says, which may be why my
previos post has been ignored.

Many of our sports members fall into the old dogs and new tricks area,
I have a feeling the more experience one has in anything, the more they
push against change, especially as we grow older.

I must disagree with Dereks' statement on measuring tension as well, it
is a simple thing to do. Perhaps it hasnt been done, sure, but its not
hard. (Caveat- I sell loadcells and measurement equipment for a
living)

As I have stated, If we can identify we have a problem (we do, people
have died) why would we not change? Technology is allowing change,
embrace it.
If, with respect of time, we see we were wrong and can change back,
what harm? At least we tried.

We can set up winches to do any damn thing we like, every time,
regardless of wind gusts, temperature changes, altitute differences,
ballast, number of pilots, student requirements, winchperson ability,
emergency airspace violations etc, etc. So lets!

If you dis-agree, dont fly off the new winch, simple!


Bagger




--
bagmaker

On Mar 25, 3:59*am, bagmaker
wrote:
;687487 Wrote:





Bill said:
"... the tension should be the maximum safe value."

OK, let me try this again. Maybe you'll understand this question:

1. In your opinion, what is the maximum safe value expressed in g, for
he initial launch phase?
2. Who else agrees with your position that the initial launch phase
should be aggressive? In this thread alone, nobody agrees with you.
Where are all these people? Mr. George Moore has also said he
advocates a slower launch than you do on the Yahoo groups site.
"Bill has advocated higher ground acceleration rates than I am
generally comfortable with."

I haven't heard a single person support what you advocate. Whatever
you find, please with verifiable quotes.

- And I don't know were your get your sense of what rude is, but
publicly and falsely claiming I am misrepresenting my identity without
any proof on your part what so ever, certainly is rude behavior.

I would support a fair bit of what Bill says, which may be why my
previos post has been ignored.

Many of our sports members fall into the old dogs and new tricks area,
I have a feeling the more experience one has in anything, the more they
push against change, especially as we grow older.

I must disagree with Dereks' statement on measuring tension as well, it
is a simple thing to do. Perhaps it hasnt been done, sure, but its not
hard. (Caveat- I sell loadcells and measurement equipment for a
living)

As I have stated, If we can identify we have a problem (we do, people
have died) why would we not change? Technology is allowing change,
embrace it.
If, with respect of time, we see we were wrong and can change back,
what harm? At least we tried.

We can set up winches to do any damn thing we like, every time,
regardless of wind gusts, temperature changes, altitute differences,
ballast, number of pilots, student requirements, winchperson ability,
emergency airspace violations etc, etc. So lets!

If you dis-agree, dont fly off the new winch, simple!

Bagger

--
bagmaker

Thanks for that.

This discussion always gets the "Safety Nazis" wringing their hands
and wailing every time. ( But never, ever, producing any hard data.)
The thing is - it's mostly a trivial "tempest in a teapot".

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. If you try
to accelerate the glider with more force than that, the link breaks in
the takeoff roll and the glider never gets airborne.

Since even the most conservative old fart thinks than .8 to .9 G is OK
for most gliders, this whole frightful affair is all about an
approximately .3G range which is buried in the 'noise'. Most pilots
can't detect the difference.

I've had brand new Tost weak links fail in the rotation phase on many
occasions as a result of too much cable tension from one of those
"underpowered US winches". I was nowhere near the limit of down
elevator authority. The most recent involved a 2-33 whose CG is at
least 3 feet above the hook and whose tiny horizontal tail severely
limits down elevator authority.

Again, the disclaimer, there are a very few mostly old gliders with a
problem which thankfully are very rare in the US. Pilots of these
should check with knowledgeable people for the special launching
technique required. Virtually all gliders in the US winch just fine.

I strongly suspect the problem is isolated to the UK, where they do
fly old gliders, and has to do with a particular new 'powerful winch'
which is capable of enormous force in first gear and which shifts to
second gear at some unknown and uncontrollable point during the
rotation phase. The tension data which IS available for this winch
looks pretty scary.

Dereks voluminous criticism of computer controlled automatic tension
winches stems from the fact that HIS favorite winch has no such
controls and he's afraid that US winch builders using Automatic
Tension Control will steal the market.

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.

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