At 17:15 26 July 2009, brianDG303 wrote:
>On Jul 26, 12:15=A0am, Derek Copeland wrote:
>> We Brits get tired of always being airbrushed out of history by
>Hollywood=
>..
>> For example there were more British and British Commonwealth (e.g.
>> Australians, Canadians) troops involved in the D Day landings than US
>> troops, but you might not have noticed this if you watch 'Saving
Private
>> Ryan' and many other similar movies.
>>
>> Throughout WW2 we bombed Germany by night without fighter cover, using
>> bombers such as the Lancaster and the Mosquito, which where less
heavily
>> amoured than a B17, but could carry a much greater weight of bombs as
a
>> result. In fact even the little unarmed twin engined Mosquito bombers
>mad=
>e
>> out of plywood could carry more bombs than a B17. I believe that they
>> didn't show up very well on radar because of their construction, so
they
>> were probably the original 'stealth bomber' =A0
>>
>> On entering the European war the USAAF was warned by the RAF that
>dayligh=
>t
>> bombing raids over Germany would be pretty suicidal, as they had
already
>> found out the hard way, but of course the Americans (as usual) thought
>> they knew best and had better technology. The rest, Schweinfurt etc,
is
>> history!
>>
>> I have to say however that the US bomber crews who took part in such
>raid=
>s
>> must have been very brave men, knowing that their tight, straight and
>lev=
>el
>> formations where sitting ducks for German radar predictive flak guns
and
>=
>a
>> well organised fighter force. It was only towards the end of the war
>when
>> the Mustangs shot down many German fighters that the odds became a
>little
>> more favourable for them.
>>
>> Derek Copeland =A0 =A0
>>
>Derek,
>Taking a single statistic (the number of troops landing on the
>Normandy beaches) may be a fact but obscures the truth. The ritish
>consider the invasion of Normandy to have begun on June 6 and ended on
>August 29 of 1944, and the casualties (Killed, missing, wounded) of
>British, Canadian, and Polish troops (there were very few Australians,
>with about a dozen casualties I think) totaled 83,045 as against the
>US losses of 125,847. These are the British numbers from the War
>Diary, 21st Army Group, but other estimates are similar.
>
>Also:
>Hollywood movies are intended to make money and not portray history.
>
>Your comment about French gratitude, we Americans like to forget that
>without the French we could never have won the war of 1776 and the
>cost to them of that help. We never thanked them much for that either.
>
>Your comment about fighting Germany to a draw is simply not
>supportable. Hitler's direction was always east but he turned west
>when England and France declared war on Germany following his invasion
>of Poland. He defeated France and put England in a box, then turned
>east again. Two fatal errors in judgment, of which he was in the habit
>of making.
>
>
Come to mention it, we Brits have never received much in the way of
gratitude from the Yanks for supporting George W Bush's futile and
counter productive invasions of Iraq and Afghanistan! So much for the
'special relationship'....!

Hitler's Germany tried very hard to invade the UK as they had already
done to Poland, Belgium, Holland and France and were beaten off, losing a
fair proportion of the Luftwaffe in the process. As well as shooting down
many attacking aircraft, the RAF also bombed the invasion fleets in the
French ports pretty well non stop, making the invasion non-viable. These
are historical facts.

Derek Copeland

On Jul 26, 11:45*am, Del C > wrote:
> At 17:15 26 July 2009, brianDG303 wrote:
>
> >On Jul 26, 12:15=A0am, Derek Copeland *wrote:
> >> We Brits get tired of always being airbrushed out of history by
> >Hollywood=
> >..
> >> For example there were more British and British Commonwealth (e.g.
> >> Australians, Canadians) troops involved in the D Day landings than US
> >> troops, but you might not have noticed this if you watch 'Saving
> Private
> >> Ryan' and many other similar movies.
>
> >> Throughout WW2 we bombed Germany by night without fighter cover, using
> >> bombers such as the Lancaster and the Mosquito, which where less
> heavily
> >> amoured than a B17, but could carry a much greater weight of bombs as
> a
> >> result. In fact even the little unarmed twin engined Mosquito bombers
> >mad=
> >e
> >> out of plywood could carry more bombs than a B17. I believe that they
> >> didn't show up very well on radar because of their construction, so
> they
> >> were probably the original 'stealth bomber' =A0
>
> >> On entering the European war the USAAF was warned by the RAF that
> >dayligh=
> >t
> >> bombing raids over Germany would be pretty suicidal, as they had
> already
> >> found out the hard way, but of course the Americans (as usual) thought
> >> they knew best and had better technology. The rest, Schweinfurt etc,
> is
> >> history!
>
> >> I have to say however that the US bomber crews who took part in such
> >raid=
> >s
> >> must have been very brave men, knowing that their tight, straight and
> >lev=
> >el
> >> formations where sitting ducks for German radar predictive flak guns
> and
> >=
> >a
> >> well organised fighter force. It was only towards the end of the war
> >when
> >> the Mustangs shot down many German fighters that the odds became a
> >little
> >> more favourable for them.
>
> >> Derek Copeland =A0 =A0
>
> >Derek,
> >Taking a single statistic (the number of troops landing on the
> >Normandy beaches) may be a fact but obscures the truth. The ritish
> >consider the invasion of Normandy to have begun on June 6 and ended on
> >August 29 of 1944, and the casualties (Killed, missing, wounded) of
> >British, Canadian, and Polish troops (there were very few Australians,
> >with about a dozen casualties I think) totaled 83,045 as against the
> >US losses of 125,847. These are the British numbers from the War
> >Diary, 21st Army Group, but other estimates are similar.
>
> >Also:
> >Hollywood movies are intended to make money and not portray history.
>
> >Your comment about French gratitude, we Americans like to forget that
> >without the French we could never have won the war of 1776 and the
> >cost to them of that help. We never thanked them much for that either.
>
> >Your comment about fighting Germany to a draw is simply not
> >supportable. Hitler's direction was always east but he turned west
> >when England and France declared war on Germany following his invasion
> >of Poland. He defeated France and put England in a box, then turned
> >east again. Two fatal errors in judgment, of which he was in the habit
> >of making.
>
> Come to mention it, we Brits have never received much in the way of
> gratitude from the Yanks for supporting George W Bush's futile and
> counter productive invasions of Iraq and Afghanistan! So much for the
> 'special relationship'....!
>
> Hitler's Germany tried very hard to invade the UK as they had already
> done to Poland, Belgium, Holland and France and were beaten off, losing a
> fair proportion of the Luftwaffe in the process. As well as shooting down
> many attacking aircraft, the RAF also bombed the invasion fleets in the
> French ports pretty well non stop, making the invasion non-viable. These
> are historical facts.
>
> Derek Copeland

Derek,
agree with the facts, just not the conclusions. The UK won the Battle
of Britain (good job that!) but if Hitler's #1 goal had been to defeat
Britain he probably could have done so, I'm not convinced GB 'fought
him to a draw'. Hitler was defeated in large part by the temperature
and terrain of Russia as was Napoleon before him, along with Russia's
ability to take almost unlimited casualties in the process, and Russia
was always the goal.

Perhaps we should leave the Iraq/Afghanistan theater for another day.
Do they winch-launch there?


I'll be over in six weeks walking the ground of the AFalaise if you
can come over we could get into it and enjoy

As interesting as it is the discussion about who did what in the last war
has about as much relevance to gliding and safe winching as a tesion
controlled winch.

The differences are too numerous to mention except that a Spitfire,
Hurricane and Mustang all worked and did a useful job, unlike the mythical
tension controlled winch.

At 18:45 26 July 2009, Del C wrote:

>Hitler's Germany tried very hard to invade the UK as they had already
>done to Poland, Belgium, Holland and France and were beaten off, losing
a
>fair proportion of the Luftwaffe in the process. As well as shooting
down
>many attacking aircraft, the RAF also bombed the invasion fleets in the
>French ports pretty well non stop, making the invasion non-viable. These
>are historical facts.

Germany could have swept up the British troops at Dunkirk,
and then immediately invaded with a pretty good chance of
success. But Hitler dithered, and listened to Goering, and
blew his chance. He really did make quite a few decisions
that, in hindsight at least, were disastrous. We should,
I suppose, be grateful for that.

Jim Beckman

The 'constant tension' theory of winch launching was dreamed up by
someone in the US who has no practical experience of winch launching
whatsoever!

So far nobody has managed to built a true tension winch (which would
measure actual cable tension), so we don't know if the theory would work
or not. The concept seems to have become a bit of a Holy Grail in the US,
which is probably inhibiting the design and building of more conventional
winches that would work just fine.

On the Yahoo Winch Design site I have suggested carrying out some
autotowing experiments, where it would fairly easy to mount an in-line
load cell to find out if CT would work, but this suggestion was rejected
by the above person and his followers as not being relevant due to the
mass and inertia of the towcar. Such an experiment would work in calm
conditions.

There are a number of constraints in real life winch launching.

1) The minimum airspeed has to be at least 1.3 x the normal stalling speed
(Vs), to avoid the risk of stalling or spinning at the increased wing
loading due to the cable pull. At the high levels of pull suggested this
might increase to 1.4 Vs.

2) The optimum climbing airspeed for best gain of height seems from
practical experience to be in the range 1.5-1.6Vs.

3) Most gliders have a fairly low maximum winch launching speed (Vw),
which is set for structural reasons. There should also be a weak link
(fuse) included in the cable line which will break before the glider does.


4) Many gliders, particularly older ones such as the K13, only have a very
limited speed range in which they will climb safely and well without
exceeding Vw. The stalling speed of a K13 can increase to over 50knots
near the top of the launch, its optimum climb speed is about 56knots and
its Vw is 58knots. Some more modern types such as the K21 are a bit more
speed tolerant.

5) You have to fly the glider in such a manner that you can always
recover from a cable break or winch power failure, and not risk a stall or
flick spin. This entails a fairly shallow initial climb followed by a
controlled rotation rate of not more than 10 degrees per second. I believe
the Germans once managed to kill 12 pilots in one year (1995) by carrying
out what are known as 'kavalier starts' where the glider climbs very
steeply straight off the ground to maximise height. We have also had a few
such accidents in the UK, always on very powerful winches so rapid
acceleration doesn't make them safe.

The theory behind constant tension is you provide a pull or tension that
is close to the breaking strain of the weak link. Thus you maximise the
pull and the height gain in accordance with the Goulthorpe formula:
h = P/W/(1+P/W) x l
where h = height, P= Pull, W = glider weight and l = notional cable run
from the point of rotation.
Thus for a Pull equal to the weight of the glider you would expect to get
a height of 50% of the effective cable length.

However, the above equation is idealised and assumes zero cable weight and
zero drag, and is based on 100% transfer of energy.

For many years I launched on very powerful manually driven Tost winches.
Many of the launches were way over Vw until you signalled too fast, but it
was quite rare to break a weak link in the early part of the climb. I
therefore suspect that the constant tension as a large fraction of the
weak link strength idea would just vastly overspeed the launches. In order
to contain the speed according to the theory, you would have to climb at an
achieved climb angle of about 60 degrees. Most gliders run out of up
elevator well below this angle. Such an angle would also represent more
than a 'kavalier start' as described above!

The other idea in the 'constant tension' theory is that the glider pilot
would control the speed by pulling back harder to slow the launch down and
easing forward to speed up. However I worry that a pilot trying to control
the speed at the same time as the winch is trying to sense and control the
tension would just lead to an oscillating or hunting situation. As a winch
driver myself, I always try to avoid 'chasing the glider pilot' as this
generally makes things worse. If I have to make a speed adjustment I just
move the throttle to a slightly different setting and then hold it still
again. The technique for controlling the airspeed from the glider end does
work on a Skylaunch winch where you are giving a constant power setting and
also works on constant torque Supacat (diesel + fluid flywheel)) winches.
With either type of winch you have to start backing off the throttle
setting near the top of the launch to avoid overspeeding the glider.

We don't know if constant tension would give a constant and appropriate
airspeed, or whether it would need to be varied for different stages of
the launch to achieve this.

Derek Copeland



At 19:45 26 July 2009, Don Johnstone wrote:
>As interesting as it is the discussion about who did what in the last
war
>has about as much relevance to gliding and safe winching as a tesion
>controlled winch.
>
>The differences are too numerous to mention except that a Spitfire,
>Hurricane and Mustang all worked and did a useful job, unlike the
mythical
>tension controlled winch.
>

As I see it the "constant tension" theory relies on being able to measure
the tension being exerted on the glider release at the winch drum. Quite
how this might be achieved is very puzzling and has no relevance to the
information required to give a safe and effective launch.
If you were to say that measuring the tension at the glider release and
using telemetry to pass this information to the winch then that might
indeed work, however if you were going to the trouble of doing that you
might as well send useful information, like the airspeed of the glider, so
the winch driver could maintain a constant speed.
Cable tension during a winch launch has sod all to do with anything except
as an indicator to the winch driver of possible over or underspeed. It is
the speed which is of relevance and importance.

At 13:15 27 July 2009, Del C wrote:
>The 'constant tension' theory of winch launching was dreamed up by
>someone in the US who has no practical experience of winch launching
>whatsoever!
>
>So far nobody has managed to built a true tension winch (which would
>measure actual cable tension), so we don't know if the theory would
work
>or not. The concept seems to have become a bit of a Holy Grail in the
US,
>which is probably inhibiting the design and building of more
conventional
>winches that would work just fine.
>
>On the Yahoo Winch Design site I have suggested carrying out some
>autotowing experiments, where it would fairly easy to mount an in-line
>load cell to find out if CT would work, but this suggestion was rejected
>by the above person and his followers as not being relevant due to the
>mass and inertia of the towcar. Such an experiment would work in calm
>conditions.
>
>There are a number of constraints in real life winch launching.
>
>1) The minimum airspeed has to be at least 1.3 x the normal stalling
speed
>(Vs), to avoid the risk of stalling or spinning at the increased wing
>loading due to the cable pull. At the high levels of pull suggested this
>might increase to 1.4 Vs.
>
>2) The optimum climbing airspeed for best gain of height seems from
>practical experience to be in the range 1.5-1.6Vs.
>
>3) Most gliders have a fairly low maximum winch launching speed (Vw),
>which is set for structural reasons. There should also be a weak link
>(fuse) included in the cable line which will break before the glider
does.
>
>
>4) Many gliders, particularly older ones such as the K13, only have a
very
>limited speed range in which they will climb safely and well without
>exceeding Vw. The stalling speed of a K13 can increase to over 50knots
>near the top of the launch, its optimum climb speed is about 56knots and
>its Vw is 58knots. Some more modern types such as the K21 are a bit more
>speed tolerant.
>
>5) You have to fly the glider in such a manner that you can always
>recover from a cable break or winch power failure, and not risk a stall
or
>flick spin. This entails a fairly shallow initial climb followed by a
>controlled rotation rate of not more than 10 degrees per second. I
believe
>the Germans once managed to kill 12 pilots in one year (1995) by
carrying
>out what are known as 'kavalier starts' where the glider climbs very
>steeply straight off the ground to maximise height. We have also had a
few
>such accidents in the UK, always on very powerful winches so rapid
>acceleration doesn't make them safe.
>
>The theory behind constant tension is you provide a pull or tension that
>is close to the breaking strain of the weak link. Thus you maximise the
>pull and the height gain in accordance with the Goulthorpe formula:
>h = P/W/(1+P/W) x l
>where h = height, P= Pull, W = glider weight and l = notional cable run
>from the point of rotation.
>Thus for a Pull equal to the weight of the glider you would expect to
get
>a height of 50% of the effective cable length.
>
>However, the above equation is idealised and assumes zero cable weight
and
>zero drag, and is based on 100% transfer of energy.
>
>For many years I launched on very powerful manually driven Tost winches.
>Many of the launches were way over Vw until you signalled too fast, but
it
>was quite rare to break a weak link in the early part of the climb. I
>therefore suspect that the constant tension as a large fraction of the
>weak link strength idea would just vastly overspeed the launches. In
order
>to contain the speed according to the theory, you would have to climb at
>an
>achieved climb angle of about 60 degrees. Most gliders run out of up
>elevator well below this angle. Such an angle would also represent more
>than a 'kavalier start' as described above!
>
>The other idea in the 'constant tension' theory is that the glider
pilot
>would control the speed by pulling back harder to slow the launch down
and
>easing forward to speed up. However I worry that a pilot trying to
control
>the speed at the same time as the winch is trying to sense and control
the
>tension would just lead to an oscillating or hunting situation. As a
winch
>driver myself, I always try to avoid 'chasing the glider pilot' as
this
>generally makes things worse. If I have to make a speed adjustment I
just
>move the throttle to a slightly different setting and then hold it still
>again. The technique for controlling the airspeed from the glider end
does
>work on a Skylaunch winch where you are giving a constant power setting
>and
>also works on constant torque Supacat (diesel + fluid flywheel))
winches.
>With either type of winch you have to start backing off the throttle
>setting near the top of the launch to avoid overspeeding the glider.
>
>We don't know if constant tension would give a constant and appropriate
>airspeed, or whether it would need to be varied for different stages of
>the launch to achieve this.
>
>Derek Copeland
>
>
>
>At 19:45 26 July 2009, Don Johnstone wrote:
>>As interesting as it is the discussion about who did what in the last
>war
>>has about as much relevance to gliding and safe winching as a tesion
>>controlled winch.
>>
>>The differences are too numerous to mention except that a Spitfire,
>>Hurricane and Mustang all worked and did a useful job, unlike the
>mythical
>>tension controlled winch.
>>
>

At Feshiebridge, Scotland, AIUI they developed telemetry for
indicating glider airspeed to the winch driver, and it was said to
work very well. IIRC, it did not send an airspeed number in knots, but
rather an indication of too slow, a bit slow, OK, a bit fast, or too
fast (or something like that) which is what the winch driver really
needs to know, they believed. The unit in the glider was calibrated
for the glider type.

It needs somebody with first hand experience of it to tell more, and I
don’t know if it has been kept going.

Chris N.

I suspect fitting each and every glider with a telemetry transmitter
would be prohibitively expensive and resisted by most. A member of my
club did this as an experimental demonstration and I was able to drive
the winch to the appropriate airspeed. Getting accurate airspeed from
a rope mounted device for the whole fleet could be problematic.
Tension telemetry would be much easier to construct and ruggedize and
limiting tension by glider type (and loading) is doable, probably more
easily with hydraulically or electrically driven drums than with the
reciprocating and rotating weight of IC engines in a direct drive
(including automatic transmissions and drive trains) where airspeed
output would be more easily used. Tension control should allow for
wind gradients and shears but the control algorithms need to smooth
the changes to avoid surges and hunting. Manually driven winches
should not be discounted, but I have some ideas about standardization
of controls and operating methods.

Frank Whiteley


On Jul 27, 9:30*am, Don Johnstone > wrote:
> As I see it the "constant tension" theory relies on being able to measure
> the tension being exerted on the glider release at the winch drum. Quite
> how this might be achieved is very puzzling and has no relevance to the
> information required to give a safe and effective launch.
> If you were to say that measuring the tension at the glider release and
> using telemetry to pass this information to the winch then that might
> indeed work, however if you were going to the trouble of doing that you
> might as well send useful information, like the airspeed of the glider, so
> the winch driver could maintain a constant speed.
> Cable tension during a winch launch has sod all to do with anything except
> as an indicator to the winch driver of possible over or underspeed. It is
> the speed which is of relevance and importance.
>
> At 13:15 27 July 2009, Del C wrote:
>
> >The 'constant tension' theory of winch launching was dreamed up by
> >someone in the US who has no practical experience of winch launching
> >whatsoever!
>
> >So far nobody has managed to built a true tension winch (which would
> >measure actual cable tension), so we don't know if the theory would
> work
> >or not. The concept seems to have become a bit of a Holy Grail in the
> US,
> >which is probably inhibiting the design and building of more
> conventional
> >winches that would work just fine.
>
> >On the Yahoo Winch Design site I have suggested carrying out some
> >autotowing experiments, where it would fairly easy to mount an in-line
> >load cell to find out if CT would work, but this suggestion was rejected
> >by the above person and his followers as not being relevant due to the
> >mass and inertia of the towcar. Such an experiment would work in calm
> >conditions.
>
> >There are a number of constraints in real life winch launching.
>
> >1) The minimum airspeed has to be at least 1.3 x the normal stalling
> speed
> >(Vs), to avoid the risk of stalling or spinning at the increased wing
> >loading due to the cable pull. At the high levels of pull suggested this
> >might increase to 1.4 Vs.
>
> >2) The optimum climbing airspeed for best gain of height seems from
> >practical experience to be in the range 1.5-1.6Vs.
>
> >3) Most gliders have a fairly low maximum winch launching speed (Vw),
> >which is set for structural reasons. There should also be a weak link
> >(fuse) included in the cable line which will break before the glider
> does.
>
> >4) Many gliders, particularly older ones such as the K13, only have a
> very
> >limited speed range in which they will climb safely and well without
> >exceeding Vw. The stalling speed of a K13 can increase to over 50knots
> >near the top of the launch, its optimum climb speed is about 56knots and
> >its Vw is 58knots. Some more modern types such as the K21 are a bit more
> >speed tolerant.
>
> >5) You have to fly the glider in such a manner *that you can always
> >recover from a cable break or winch power failure, and not risk a stall
> or
> >flick spin. This entails a fairly shallow initial climb followed by a
> >controlled rotation rate of not more than 10 degrees per second. I
> believe
> >the Germans once managed to kill 12 pilots in one year (1995) by
> carrying
> >out what are known as 'kavalier starts' where the glider climbs very
> >steeply straight off the ground to maximise height. We have also had a
> few
> >such accidents in the UK, always on very powerful winches so rapid
> >acceleration doesn't make them safe.
>
> >The theory behind constant tension is you provide a pull or tension that
> >is close to the breaking strain of the weak link. Thus you maximise the
> >pull and the height gain in accordance with the Goulthorpe formula:
> >h = P/W/(1+P/W) x l
> >where h = height, P= Pull, W = glider weight and l = notional cable run
> >from the point of rotation.
> >Thus for a Pull equal to the weight of the glider you would expect to
> get
> >a height of 50% of the effective cable length.
>
> >However, the above equation is idealised and assumes zero cable weight
> and
> >zero drag, and is based on 100% transfer of energy.
>
> >For many years I launched on very powerful manually driven Tost winches.
> >Many of the launches were way over Vw until you signalled too fast, but
> it
> >was quite rare to break a weak link in the early part of the climb. I
> >therefore suspect that the constant tension as a large fraction of the
> >weak link strength idea would just vastly overspeed the launches. In
> order
> >to contain the speed according to the theory, you would have to climb at
> >an
> >achieved climb angle of about 60 degrees. Most gliders run out of up
> >elevator well below this angle. Such an angle would also represent more
> >than a 'kavalier start' as described above!
>
> >The other idea in the 'constant tension' theory is that the glider
> pilot
> >would control the speed by pulling back harder to slow the launch down
> and
> >easing forward to speed up. However I worry that a pilot trying to
> control
> >the speed at the same time as the winch is trying to sense and control
> the
> >tension would just lead to an oscillating or hunting situation. As a
> winch
> >driver myself, I always try to avoid 'chasing the glider pilot' as
> this
> >generally makes things worse. If I have to make a speed adjustment I
> just
> >move the throttle to a slightly different setting and then hold it still
> >again. The technique for controlling the airspeed from the glider end
> does
> >work on a Skylaunch winch where you are giving a constant power setting
> >and
> >also works on constant torque Supacat (diesel + fluid flywheel))
> winches.
> >With either type of winch you have to start backing off the throttle
> >setting near the top of the launch to avoid overspeeding the glider. *
>
> >We don't know if constant tension would give a constant and appropriate
> >airspeed, or whether it would need to be varied for different stages of
> >the launch to achieve this.
>
> >Derek Copeland
>
> >At 19:45 26 July 2009, Don Johnstone wrote:
> >>As interesting as it is the discussion about who did what in the last
> >war
> >>has about as much relevance to gliding and safe winching as a tesion
> >>controlled winch.
>
> >>The differences are too numerous to mention except that a Spitfire,
> >>Hurricane and Mustang all worked and did a useful job, unlike the
> >mythical
> >>tension controlled winch.

Don Johnstone wrote:
> ...
> If you were to say that measuring the tension at the glider release and
> using telemetry to pass this information to the winch then that might
> indeed work, however if you were going to the trouble of doing that you
> might as well send useful information, like the airspeed of the glider, so
> the winch driver could maintain a constant speed.
> Cable tension during a winch launch has sod all to do with anything except
> as an indicator to the winch driver of possible over or underspeed. It is
> the speed which is of relevance and importance.
>

We have recently tested the Launch Assistent that is sold by Skylaunch,
http://www.skylaunchuk.com/index.htm
and have found that is can be (as the name indicates) an *assistant* to
the winch driver to help him/her judge the speed of the plane. It helps
escpecially unexperienced winch drivers, or in adverse conditions like
shearing winds within the launch.

After 20 years of experience as a winch driver and winch instructor
(Tost winch) I still believe a well instructed and experienced winch
driver (and all winch drivers should have a certain minimum of launches
per year) is able to judge and control the launch as good (or even
better) than any automated (tension-controlled) system, that in the end
also relies on the correct behavior of the pilot instead of the winch
driver.

--
Peter Scholz
ASW 24 JEB

Skylaunch sell a telemetry system called 'Launch Assistant' which relays
the actual airspeed of the glider to an LCD display mounted somewhere in
the view of the driver. It costs a few hundred dollars in total. See:

http://www.skylaunchuk.com/

Derek Copeland


At 16:49 27 July 2009, Chris Nicholas wrote:
>
>At Feshiebridge, Scotland, AIUI they developed telemetry for
>indicating glider airspeed to the winch driver, and it was said to
>work very well. IIRC, it did not send an airspeed number in knots, but
>rather an indication of too slow, a bit slow, OK, a bit fast, or too
>fast (or something like that) which is what the winch driver really
>needs to know, they believed. The unit in the glider was calibrated
>for the glider type.
>
>It needs somebody with first hand experience of it to tell more, and I
>don=92t know if it has been kept going.
>
>Chris N.
>
>

At 17:23 27 July 2009, Peter Scholz wrote:
>Don Johnstone wrote:
>> ...
>> If you were to say that measuring the tension at the glider release
and
>> using telemetry to pass this information to the winch then that might
>> indeed work, however if you were going to the trouble of doing that
you
>> might as well send useful information, like the airspeed of the
glider,
>so
>> the winch driver could maintain a constant speed.
>> Cable tension during a winch launch has sod all to do with anything
>except
>> as an indicator to the winch driver of possible over or underspeed. It
>is
>> the speed which is of relevance and importance.
>>
>
>We have recently tested the Launch Assistent that is sold by Skylaunch,
>http://www.skylaunchuk.com/index.htm
>and have found that is can be (as the name indicates) an *assistant* to
>the winch driver to help him/her judge the speed of the plane. It helps
>escpecially unexperienced winch drivers, or in adverse conditions like
>shearing winds within the launch.
>
>After 20 years of experience as a winch driver and winch instructor
>(Tost winch) I still believe a well instructed and experienced winch
>driver (and all winch drivers should have a certain minimum of launches
>per year) is able to judge and control the launch as good (or even
>better) than any automated (tension-controlled) system, that in the end
>also relies on the correct behavior of the pilot instead of the winch
>driver.
>
>--
>Peter Scholz
>ASW 24 JEB


Well, there you have it, problem solved by superior and relevant British
engineering and at reasonable cost.
Tension controlled winches are obsolete already as we have jumped a
stage.
Any move to automatic winch driving would be a big big mistake, a good,
well trained winch driver is the best way of ensuring safety.
Automatic takeoff, automatic landing, automatic crash.

Peter Scholz wrote:
> Don Johnstone wrote:
>> ...
>> If you were to say that measuring the tension at the glider release and
>> using telemetry to pass this information to the winch then that might
>> indeed work, however if you were going to the trouble of doing that you
>> might as well send useful information, like the airspeed of the
>> glider, so
>> the winch driver could maintain a constant speed.
>> Cable tension during a winch launch has sod all to do with anything
>> except
>> as an indicator to the winch driver of possible over or underspeed. It is
>> the speed which is of relevance and importance.
>>
>
> We have recently tested the Launch Assistent that is sold by Skylaunch,
> http://www.skylaunchuk.com/index.htm
> and have found that is can be (as the name indicates) an *assistant* to
> the winch driver to help him/her judge the speed of the plane. It helps
> escpecially unexperienced winch drivers, or in adverse conditions like
> shearing winds within the launch.
>
> After 20 years of experience as a winch driver and winch instructor
> (Tost winch) I still believe a well instructed and experienced winch
> driver (and all winch drivers should have a certain minimum of launches
> per year) is able to judge and control the launch as good (or even
> better) than any automated (tension-controlled) system, that in the end
> also relies on the correct behavior of the pilot instead of the winch
> driver.
>
> --
> Peter Scholz
> ASW 24 JEB

There has been some interesting scientific research beeing done on this
topic by the Akaflieg group of the University of Karlsruhe (Germany)
some years ago. It would go to far describing it in detail, but one
diagram where they measured a winch launch is quite interesting:

http://www.akaflieg.uni-karlsruhe.de/projekte/asts/Der%20Gesamte%20Schlepp.pdf

The parameters measured were:
Height (blue)
Airspeed (magenta)
Torque at winch drum axle (dark blue)
elevator position (green)
Acceleration in x-direction (brown)
Acceleration in z-direction (yellow)

It shows that what appears to be a relative smooth winch launch, looking
at airspeed and height, has a quite significant variation in torque,
elevator position and acceleration.

The findings of this sientific work in one simple sentence: A simple
"constant tension" cannot cope with all the parameters that influence a
winch launch and that are dependent on eacht other.

So the (also economically) best approach would be to aid the winch
driver doing his job right instead of inventing a highly sophisticated
fuzzy logic system that may take into account all parameters to act as
well as a winch driver.

The goal is not to have winch launches that are all perfect and one as
optimal as the other, but the goal has to be to have safe winch launches
with an acceptable performance. And safety lies within a quite large
corridor.

--
Peter Scholz
ASW 24 JEB

Back to metrics - if you are measuring the wrong thing, the best you can
hope for is that it is irrelevant...

So - for a "good" winch, there are a couple of things you may want to
measure.

How much does it cost?
- Capital to purchase (and how long it lasts)
- Operating cost to service and run
- Repair cost when something breaks (including damage to the gliding fleet)
- How fast can it launch relative to requirement

Is it safe?
- How easy is it to control the acceleration?
- How easy is it to achieve the correct speed in all phases of the launch?
- How well does the set up accommodate for unexpected events (big
thermal, windshear, pilot error)

So far my experience and inclination tend to support the theory that the
key requirements to satisfy the above favour simplicity and human
control. I am a computer / automation professional, but there are some
things I would prefer a human doing. Driving and controlling the winch
is one of those. There are too many variables to concern yourself with.

As an exercise - Let's test a theory. (in the empirical sciences the
difference between a theory and an idea being that a theory can be
disproved by observation and deduction).

Lets say that my theory is that relying on a single metric for control
of a winch - specifically cable tension as measured anywhere on the
cable or drum is safe.


OK - can we disprove that? -

Let's say for argument that the pilot fails to rotate appropriately. For
any number of reasons. Constant tension must be applied in this model,
so energy transfer continues to be done and the glider speed increases
as there is no increase in potential energy.
After a very short period the glider is past Vw and the pilot dare not
rotate. If the pilot is incapable of, or is slow at releasing (for
whatever reason) the speed will continue to increase, as the available
landing area is consumed at an ever increasing rate. Clearly this is
not a safe situation.

Let's argue a different approach - Now let's say for argument that the
belief that the control over tension in the cable is so good that we
have disregarded the weak link specification and are relying on the
ability of the system to regulate tension. Now we follow a launch where
the cable predictably hooks on some grass causing a bow in the run. At
the all out the grass resists the considerable lateral pressure
momentarily, the winch achieves designed tension. Then the rope/wire
breaks free of the grass and the bow becomes slack cable. In attempting
to maintain tension the winch accelerates, removing the slack. At some
point in time the cable becomes straight, all slack has been absorbed
and the cable tension rapidly increases past the design tension.
Consider the reaction time of the system, given the rotational inertia
of the drum and transmission, to say nothing of the whip action on the
cable as the wave travels toward the aircraft. Once again I fail to see
how this is going to be safe.

In this case the judgement available in a manual control system
increases safety - you can't rely on automation to magically create
safety.

So what can we deduce?

Basically you are trying to measure how well a complex and potentially
dangerous operation is progressing. In a constantly changing medium,
with multiple sources of error and variance (not least caused by the
multiple human inputs) I know it is very tempting to believe that there
is one thing you have to worry about and it will all work out perfectly.
Regrettably this is a little like perfect landings. Rumour has it there
are only three things you have to get right. Problem is no-one can agree
on which three things...

In a winch launch one needs to decide on what to do based on aircraft
speed, height, position relative to the available runways, terrain and
traffic. Always considering the capabilities of the aircraft, pilot,
winch driver and not least the prevailing weather.

Clearly - Relying on one metric is dangerous oversimplification.
Now a tension limited winch may be a good thing, and a winch that can
smooth the tension in the cable to avoid spikes would be desirable.
And certainly I have seen some scary old manual winches. Funny thing is
- as long as you have people who communicate about what the performance
and experience is, and who learn and adapt to the vagaries of whatever
winch they are using. It tends to work. Usually surprisingly well.

So - in reality the technically complex winches use a lot of technology,
and then rely on the same judgement that a lot simpler and cheaper winch
uses.

To quote Hydrowinch
"The Hydrostart winch still runs on the original automatic force and
speed control software. A manual override is just one of the regulatory
safety features that have been there since the winch is in operation.
Because when it comes to safety, we can only rely on the winch driver's
judgement. The automatic control system is not running the winch. It's
there to assist the winch driver maintaining a constant quality and
launch performance."

Is this system better and safer - From an engineering perspective ,
definitely. Is is better value for money and safer than the person using
it? Unfortunately not.

Now - if people put as much effort into building and using the things as
is getting put into this debate - we would be doing well.

So far - lots of attempts to substitute technology have been
unsuccessful at displacing simple , robust semi manual systems with
proven reliability and controlability. There may be a prefect winch
design out there, and so far the evidence indicates that this is
something less than over engineered.

Again I submit - the metrics that matter are safety and economy.
For safety you need reliability, and controlability.

For economy you need simplicity, robustness and maximum use of "off the
shelf" components.

The only place I could possibly see justifying a technological super
winch, would be in a very high launch intensity 7 days a week operation.

If anyone can, and desires to make a better winch than any of the
commercial alternatives out there, profitably. Please do so - there are
customers who would love to make you commercially successful.

If you want to , and can afford to use/build something as far into the
overkill region as a Hydrostart, be grateful and enjoy the toys. Just
don't expect great economy/commercial success. As a technocrat - I would
love one. As a club member it would be a financial, maintenance and
operational disaster. Our best winch driver loves spending hours a day
getting the best out of our ancient single drum - but he can't use a
computer... Personally, I would love to be able to put a new "Skylaunch"
style winch at his disposal. It's the same reason the much maligned
Windows OS dominates desktops. It is not the "best" but it works for
most...

Bruce

Damn - I'm feeding trolls....

Don Johnstone wrote:
> As I see it the "constant tension" theory relies on being able to measure
> the tension being exerted on the glider release at the winch drum. Quite
> how this might be achieved is very puzzling and has no relevance to the
> information required to give a safe and effective launch.
> If you were to say that measuring the tension at the glider release and
> using telemetry to pass this information to the winch then that might
> indeed work, however if you were going to the trouble of doing that you
> might as well send useful information, like the airspeed of the glider, so
> the winch driver could maintain a constant speed.
> Cable tension during a winch launch has sod all to do with anything except
> as an indicator to the winch driver of possible over or underspeed. It is
> the speed which is of relevance and importance.
>
> At 13:15 27 July 2009, Del C wrote:
>> The 'constant tension' theory of winch launching was dreamed up by
>> someone in the US who has no practical experience of winch launching
>> whatsoever!
>>
>> So far nobody has managed to built a true tension winch (which would
>> measure actual cable tension), so we don't know if the theory would
> work
>> or not. The concept seems to have become a bit of a Holy Grail in the
> US,
>> which is probably inhibiting the design and building of more
> conventional
>> winches that would work just fine.
>>
>> On the Yahoo Winch Design site I have suggested carrying out some
>> autotowing experiments, where it would fairly easy to mount an in-line
>> load cell to find out if CT would work, but this suggestion was rejected
>> by the above person and his followers as not being relevant due to the
>> mass and inertia of the towcar. Such an experiment would work in calm
>> conditions.
>>
>> There are a number of constraints in real life winch launching.
>>
>> 1) The minimum airspeed has to be at least 1.3 x the normal stalling
> speed
>> (Vs), to avoid the risk of stalling or spinning at the increased wing
>> loading due to the cable pull. At the high levels of pull suggested this
>> might increase to 1.4 Vs.
>>
>> 2) The optimum climbing airspeed for best gain of height seems from
>> practical experience to be in the range 1.5-1.6Vs.
>>
>> 3) Most gliders have a fairly low maximum winch launching speed (Vw),
>> which is set for structural reasons. There should also be a weak link
>> (fuse) included in the cable line which will break before the glider
> does.
>>
>> 4) Many gliders, particularly older ones such as the K13, only have a
> very
>> limited speed range in which they will climb safely and well without
>> exceeding Vw. The stalling speed of a K13 can increase to over 50knots
>> near the top of the launch, its optimum climb speed is about 56knots and
>> its Vw is 58knots. Some more modern types such as the K21 are a bit more
>> speed tolerant.
>>
>> 5) You have to fly the glider in such a manner that you can always
>> recover from a cable break or winch power failure, and not risk a stall
> or
>> flick spin. This entails a fairly shallow initial climb followed by a
>> controlled rotation rate of not more than 10 degrees per second. I
> believe
>> the Germans once managed to kill 12 pilots in one year (1995) by
> carrying
>> out what are known as 'kavalier starts' where the glider climbs very
>> steeply straight off the ground to maximise height. We have also had a
> few
>> such accidents in the UK, always on very powerful winches so rapid
>> acceleration doesn't make them safe.
>>
>> The theory behind constant tension is you provide a pull or tension that
>> is close to the breaking strain of the weak link. Thus you maximise the
>> pull and the height gain in accordance with the Goulthorpe formula:
>> h = P/W/(1+P/W) x l
>> where h = height, P= Pull, W = glider weight and l = notional cable run
>>from the point of rotation.
>> Thus for a Pull equal to the weight of the glider you would expect to
> get
>> a height of 50% of the effective cable length.
>>
>> However, the above equation is idealised and assumes zero cable weight
> and
>> zero drag, and is based on 100% transfer of energy.
>>
>> For many years I launched on very powerful manually driven Tost winches.
>> Many of the launches were way over Vw until you signalled too fast, but
> it
>> was quite rare to break a weak link in the early part of the climb. I
>> therefore suspect that the constant tension as a large fraction of the
>> weak link strength idea would just vastly overspeed the launches. In
> order
>> to contain the speed according to the theory, you would have to climb at
>> an
>> achieved climb angle of about 60 degrees. Most gliders run out of up
>> elevator well below this angle. Such an angle would also represent more
>> than a 'kavalier start' as described above!
>>
>> The other idea in the 'constant tension' theory is that the glider
> pilot
>> would control the speed by pulling back harder to slow the launch down
> and
>> easing forward to speed up. However I worry that a pilot trying to
> control
>> the speed at the same time as the winch is trying to sense and control
> the
>> tension would just lead to an oscillating or hunting situation. As a
> winch
>> driver myself, I always try to avoid 'chasing the glider pilot' as
> this
>> generally makes things worse. If I have to make a speed adjustment I
> just
>> move the throttle to a slightly different setting and then hold it still
>> again. The technique for controlling the airspeed from the glider end
> does
>> work on a Skylaunch winch where you are giving a constant power setting
>> and
>> also works on constant torque Supacat (diesel + fluid flywheel))
> winches.
>> With either type of winch you have to start backing off the throttle
>> setting near the top of the launch to avoid overspeeding the glider.
>>
>> We don't know if constant tension would give a constant and appropriate
>> airspeed, or whether it would need to be varied for different stages of
>> the launch to achieve this.
>>
>> Derek Copeland
>>
>>
>>
>> At 19:45 26 July 2009, Don Johnstone wrote:
>>> As interesting as it is the discussion about who did what in the last
>> war
>>> has about as much relevance to gliding and safe winching as a tesion
>>> controlled winch.
>>>
>>> The differences are too numerous to mention except that a Spitfire,
>>> Hurricane and Mustang all worked and did a useful job, unlike the
>> mythical
>>> tension controlled winch.
>>>

Look at what MEL does -

http://www.machinefabriek-el.nl/content_16.asp

This is the manufacturer to the reasonably conventional "Leopard" winch
and of the "van Gelder" - probably the most sophisticated winch actually
working.

I wonder what proportion they are made in.

But anyway - as examples.
Note the engines are Volvo Penta diesel...
And they measure lots of things, and still get manually driven - albeit
with exquisite control.

Interestingly there are reports of clubs reverting from van Gelder to
Skylaunch (or equivalent) with retrieve setups with better launch rates.
Something to do with complexity and maintainability and cost. Any one
with actual experience?

Bruce

Bruce wrote:
> Back to metrics - if you are measuring the wrong thing, the best you can
> hope for is that it is irrelevant...
>
> So - for a "good" winch, there are a couple of things you may want to
> measure.
>
> How much does it cost?
> - Capital to purchase (and how long it lasts)
> - Operating cost to service and run
> - Repair cost when something breaks (including damage to the gliding fleet)
> - How fast can it launch relative to requirement
>
> Is it safe?
> - How easy is it to control the acceleration?
> - How easy is it to achieve the correct speed in all phases of the launch?
> - How well does the set up accommodate for unexpected events (big
> thermal, windshear, pilot error)
>
> So far my experience and inclination tend to support the theory that the
> key requirements to satisfy the above favour simplicity and human
> control. I am a computer / automation professional, but there are some
> things I would prefer a human doing. Driving and controlling the winch
> is one of those. There are too many variables to concern yourself with.
>
> As an exercise - Let's test a theory. (in the empirical sciences the
> difference between a theory and an idea being that a theory can be
> disproved by observation and deduction).
>
> Lets say that my theory is that relying on a single metric for control
> of a winch - specifically cable tension as measured anywhere on the
> cable or drum is safe.
>
>
> OK - can we disprove that? -
>
> Let's say for argument that the pilot fails to rotate appropriately. For
> any number of reasons. Constant tension must be applied in this model,
> so energy transfer continues to be done and the glider speed increases
> as there is no increase in potential energy.
> After a very short period the glider is past Vw and the pilot dare not
> rotate. If the pilot is incapable of, or is slow at releasing (for
> whatever reason) the speed will continue to increase, as the available
> landing area is consumed at an ever increasing rate. Clearly this is
> not a safe situation.
>
> Let's argue a different approach - Now let's say for argument that the
> belief that the control over tension in the cable is so good that we
> have disregarded the weak link specification and are relying on the
> ability of the system to regulate tension. Now we follow a launch where
> the cable predictably hooks on some grass causing a bow in the run. At
> the all out the grass resists the considerable lateral pressure
> momentarily, the winch achieves designed tension. Then the rope/wire
> breaks free of the grass and the bow becomes slack cable. In attempting
> to maintain tension the winch accelerates, removing the slack. At some
> point in time the cable becomes straight, all slack has been absorbed
> and the cable tension rapidly increases past the design tension.
> Consider the reaction time of the system, given the rotational inertia
> of the drum and transmission, to say nothing of the whip action on the
> cable as the wave travels toward the aircraft. Once again I fail to see
> how this is going to be safe.
>
> In this case the judgement available in a manual control system
> increases safety - you can't rely on automation to magically create safety.
>
> So what can we deduce?
>
> Basically you are trying to measure how well a complex and potentially
> dangerous operation is progressing. In a constantly changing medium,
> with multiple sources of error and variance (not least caused by the
> multiple human inputs) I know it is very tempting to believe that there
> is one thing you have to worry about and it will all work out perfectly.
> Regrettably this is a little like perfect landings. Rumour has it there
> are only three things you have to get right. Problem is no-one can agree
> on which three things...
>
> In a winch launch one needs to decide on what to do based on aircraft
> speed, height, position relative to the available runways, terrain and
> traffic. Always considering the capabilities of the aircraft, pilot,
> winch driver and not least the prevailing weather.
>
> Clearly - Relying on one metric is dangerous oversimplification.
> Now a tension limited winch may be a good thing, and a winch that can
> smooth the tension in the cable to avoid spikes would be desirable.
> And certainly I have seen some scary old manual winches. Funny thing is
> - as long as you have people who communicate about what the performance
> and experience is, and who learn and adapt to the vagaries of whatever
> winch they are using. It tends to work. Usually surprisingly well.
>
> So - in reality the technically complex winches use a lot of technology,
> and then rely on the same judgement that a lot simpler and cheaper winch
> uses.
>
> To quote Hydrowinch
> "The Hydrostart winch still runs on the original automatic force and
> speed control software. A manual override is just one of the regulatory
> safety features that have been there since the winch is in operation.
> Because when it comes to safety, we can only rely on the winch driver's
> judgement. The automatic control system is not running the winch. It's
> there to assist the winch driver maintaining a constant quality and
> launch performance."
>
> Is this system better and safer - From an engineering perspective ,
> definitely. Is is better value for money and safer than the person using
> it? Unfortunately not.
>
> Now - if people put as much effort into building and using the things as
> is getting put into this debate - we would be doing well.
>
> So far - lots of attempts to substitute technology have been
> unsuccessful at displacing simple , robust semi manual systems with
> proven reliability and controlability. There may be a prefect winch
> design out there, and so far the evidence indicates that this is
> something less than over engineered.
>
> Again I submit - the metrics that matter are safety and economy.
> For safety you need reliability, and controlability.
>
> For economy you need simplicity, robustness and maximum use of "off the
> shelf" components.
>
> The only place I could possibly see justifying a technological super
> winch, would be in a very high launch intensity 7 days a week operation.
>
> If anyone can, and desires to make a better winch than any of the
> commercial alternatives out there, profitably. Please do so - there are
> customers who would love to make you commercially successful.
>
> If you want to , and can afford to use/build something as far into the
> overkill region as a Hydrostart, be grateful and enjoy the toys. Just
> don't expect great economy/commercial success. As a technocrat - I would
> love one. As a club member it would be a financial, maintenance and
> operational disaster. Our best winch driver loves spending hours a day
> getting the best out of our ancient single drum - but he can't use a
> computer... Personally, I would love to be able to put a new "Skylaunch"
> style winch at his disposal. It's the same reason the much maligned
> Windows OS dominates desktops. It is not the "best" but it works for
> most...
>
> Bruce
>
> Damn - I'm feeding trolls....
>
> Don Johnstone wrote:
>> As I see it the "constant tension" theory relies on being able to measure
>> the tension being exerted on the glider release at the winch drum. Quite
>> how this might be achieved is very puzzling and has no relevance to the
>> information required to give a safe and effective launch.
>> If you were to say that measuring the tension at the glider release and
>> using telemetry to pass this information to the winch then that might
>> indeed work, however if you were going to the trouble of doing that you
>> might as well send useful information, like the airspeed of the
>> glider, so
>> the winch driver could maintain a constant speed.
>> Cable tension during a winch launch has sod all to do with anything
>> except
>> as an indicator to the winch driver of possible over or underspeed. It is
>> the speed which is of relevance and importance.
>>
>> At 13:15 27 July 2009, Del C wrote:
>>> The 'constant tension' theory of winch launching was dreamed up by
>>> someone in the US who has no practical experience of winch launching
>>> whatsoever!
>>>
>>> So far nobody has managed to built a true tension winch (which would
>>> measure actual cable tension), so we don't know if the theory would
>> work
>>> or not. The concept seems to have become a bit of a Holy Grail in the
>> US,
>>> which is probably inhibiting the design and building of more
>> conventional
>>> winches that would work just fine.
>>>
>>> On the Yahoo Winch Design site I have suggested carrying out some
>>> autotowing experiments, where it would fairly easy to mount an in-line
>>> load cell to find out if CT would work, but this suggestion was rejected
>>> by the above person and his followers as not being relevant due to the
>>> mass and inertia of the towcar. Such an experiment would work in calm
>>> conditions.
>>>
>>> There are a number of constraints in real life winch launching.
>>>
>>> 1) The minimum airspeed has to be at least 1.3 x the normal stalling
>> speed
>>> (Vs), to avoid the risk of stalling or spinning at the increased wing
>>> loading due to the cable pull. At the high levels of pull suggested this
>>> might increase to 1.4 Vs.
>>>
>>> 2) The optimum climbing airspeed for best gain of height seems from
>>> practical experience to be in the range 1.5-1.6Vs.
>>>
>>> 3) Most gliders have a fairly low maximum winch launching speed (Vw),
>>> which is set for structural reasons. There should also be a weak link
>>> (fuse) included in the cable line which will break before the glider
>> does.
>>>
>>> 4) Many gliders, particularly older ones such as the K13, only have a
>> very
>>> limited speed range in which they will climb safely and well without
>>> exceeding Vw. The stalling speed of a K13 can increase to over 50knots
>>> near the top of the launch, its optimum climb speed is about 56knots and
>>> its Vw is 58knots. Some more modern types such as the K21 are a bit more
>>> speed tolerant.
>>>
>>> 5) You have to fly the glider in such a manner that you can always
>>> recover from a cable break or winch power failure, and not risk a stall
>> or
>>> flick spin. This entails a fairly shallow initial climb followed by a
>>> controlled rotation rate of not more than 10 degrees per second. I
>> believe
>>> the Germans once managed to kill 12 pilots in one year (1995) by
>> carrying
>>> out what are known as 'kavalier starts' where the glider climbs very
>>> steeply straight off the ground to maximise height. We have also had a
>> few
>>> such accidents in the UK, always on very powerful winches so rapid
>>> acceleration doesn't make them safe.
>>>
>>> The theory behind constant tension is you provide a pull or tension that
>>> is close to the breaking strain of the weak link. Thus you maximise the
>>> pull and the height gain in accordance with the Goulthorpe formula:
>>> h = P/W/(1+P/W) x l where h = height, P= Pull, W = glider weight and
>>> l = notional cable run
>>> from the point of rotation.
>>> Thus for a Pull equal to the weight of the glider you would expect to
>> get
>>> a height of 50% of the effective cable length.
>>>
>>> However, the above equation is idealised and assumes zero cable weight
>> and
>>> zero drag, and is based on 100% transfer of energy.
>>> For many years I launched on very powerful manually driven Tost winches.
>>> Many of the launches were way over Vw until you signalled too fast, but
>> it
>>> was quite rare to break a weak link in the early part of the climb. I
>>> therefore suspect that the constant tension as a large fraction of the
>>> weak link strength idea would just vastly overspeed the launches. In
>> order
>>> to contain the speed according to the theory, you would have to climb at
>>> an
>>> achieved climb angle of about 60 degrees. Most gliders run out of up
>>> elevator well below this angle. Such an angle would also represent more
>>> than a 'kavalier start' as described above!
>>>
>>> The other idea in the 'constant tension' theory is that the glider
>> pilot
>>> would control the speed by pulling back harder to slow the launch down
>> and
>>> easing forward to speed up. However I worry that a pilot trying to
>> control
>>> the speed at the same time as the winch is trying to sense and control
>> the
>>> tension would just lead to an oscillating or hunting situation. As a
>> winch
>>> driver myself, I always try to avoid 'chasing the glider pilot' as
>> this
>>> generally makes things worse. If I have to make a speed adjustment I
>> just
>>> move the throttle to a slightly different setting and then hold it still
>>> again. The technique for controlling the airspeed from the glider end
>> does
>>> work on a Skylaunch winch where you are giving a constant power setting
>>> and
>>> also works on constant torque Supacat (diesel + fluid flywheel))
>> winches.
>>> With either type of winch you have to start backing off the throttle
>>> setting near the top of the launch to avoid overspeeding the glider.
>>> We don't know if constant tension would give a constant and appropriate
>>> airspeed, or whether it would need to be varied for different stages of
>>> the launch to achieve this.
>>>
>>> Derek Copeland
>>>
>>>
>>>
>>> At 19:45 26 July 2009, Don Johnstone wrote:
>>>> As interesting as it is the discussion about who did what in the last
>>> war
>>>> has about as much relevance to gliding and safe winching as a tesion
>>>> controlled winch.
>>>> The differences are too numerous to mention except that a Spitfire,
>>>> Hurricane and Mustang all worked and did a useful job, unlike the
>>> mythical
>>>> tension controlled winch.
>>>>

At 20:39 27 July 2009, Bruce wrote:
>Look at what MEL does -
>
>http://www.machinefabriek-el.nl/content_16.asp
>
>This is the manufacturer to the reasonably conventional "Leopard" winch

>and of the "van Gelder" - probably the most sophisticated winch
actually
>working.
>
>I wonder what proportion they are made in.
>
>But anyway - as examples.
>Note the engines are Volvo Penta diesel...
>And they measure lots of things, and still get manually driven - albeit
>with exquisite control.
>
>Interestingly there are reports of clubs reverting from van Gelder to
>Skylaunch (or equivalent) with retrieve setups with better launch rates.

>Something to do with complexity and maintainability and cost. Any one
>with actual experience?
>
>Bruce
>
I flew off a Munster Van Gelder winch for 10 years and when it was working
it gave the smoothest launches I have ever had. It was fitted with
automatic drum engagement which was permanently switched off as the
drivers could do the selection much more efficiently. The control systems
were very very complex and it required many hours of maintenance during
the week to make sure it would run for the weekend. If it had been a
private club it would never have worked but the Royal Air Force had the
manpower to keep it maintained. Despite this many of the advanced systems
did not work. The winch drivers however were well trained and in the main
skillful so they worked round many of the minor problems. The winch was a
perfect example of a complex and technically advanced machine which did
not stand up to the rigors of being operated in the real world, it was
just too complex. Following that I flew for 7 years at a club using a
Skylaunch. The ability to accelerate the glider was not much less than the
MVG but it was nowhere near as smooth. The engineering was simple, one
could say agricultural, but that was it's main saving, there was nothing
complex to go wrong. The winch was made up of well tried and test indusrty
standard units which worked even with minimal servicing and I do mean
minimal. The only critisism I would make is that some of the engineering
was not agricultural enough to stand up to the abuse of club member winch
drivers. Bits fell off from time to time but the the winch engine,
transmission and drums continued to work and work well.

The MVG winch and the Skylaunch winch do the same job but the MVG does it
with much less effort. The MVG has 6 drums and it was a minor miracle if
they were all available for use. It drank deisel like there was no
tomorrow.
The Skylaunch has two drums and you could purchase 2 Skylaunch winches = 4
drums for the same amount the RAF paid for the MVG 15-20 years ago.

My current club operates a Supercat winch modified by Skylaunch to take
their engine, transmission and control. It is certainly as good as a
standard Skylaunch and has almost no downtime. They all run on LPG. (It's
what passes for cheap fuel in the UK)
With winches I believe that the KISS principle is essential

I understand that the Van Gelder (MVG) winch at Dunstable (UK) is taken out
of service for half a day each week for routine maintenance and for one
week a year for a major overhaul. This done during their competition week
when they only aerotow.

In comparison, the Skylaunch is much like a modern automobile in that you
just check the levels and give it a daily inspection (DI) every day, and
change the oil, filters and the cables every so many thousand launches.

One of the reasons Lasham decided to change from Tost to Skylaunch (apart
from better launches) was that our long serving maintenance engineer
reached retirement age and the Tosts required quite a lot of servicing and
maintenance, and an annual rebuild which took about a month each. We did
these in the winter, but we still operate then, so if anything went wrong
with the winch in service we had no backup.

When we first started winch launching we tested a 6-drum MVG winch, which
as a driver I found really impressive with lots of flashing lights and
hydraulic and pneumatic systems. However it was very expensive and it was
felt that it was rather putting all our eggs in one basket. Particularly
when we (not me BTW) had a foul up which wrapped a cable many times around
the common drive shaft and put the whole thing out of operation for nearly
two hours. In the end we decided to buy two much more basic two drum Tosts
on the grounds that if you had a major foul up or a problem on one, you
could continue to launch with the other.

Incidentally I believe that the World Record height for a glider winch
launch (over 1500m) is currently held by the relatively simple MEL Leopard
winch, and was previously held by a slightly modified Tost fitted with
higher capacity drums. See:

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

http://www.youtube.com/watch?v=-VlRd9-wxQI

Derek Copeland


At 22:45 27 July 2009, Don Johnstone wrote:
>At 20:39 27 July 2009, Bruce wrote:
>>Look at what MEL does -
>>
>>http://www.machinefabriek-el.nl/content_16.asp
>>
>>This is the manufacturer to the reasonably conventional "Leopard"
winch
>
>>and of the "van Gelder" - probably the most sophisticated winch
>actually
>>working.
>>
>>I wonder what proportion they are made in.
>>
>>But anyway - as examples.
>>Note the engines are Volvo Penta diesel...
>>And they measure lots of things, and still get manually driven - albeit

>>with exquisite control.
>>
>>Interestingly there are reports of clubs reverting from van Gelder to
>>Skylaunch (or equivalent) with retrieve setups with better launch
rates.
>
>>Something to do with complexity and maintainability and cost. Any one
>>with actual experience?
>>
>>Bruce
>>
>I flew off a Munster Van Gelder winch for 10 years and when it was
working
>it gave the smoothest launches I have ever had. It was fitted with
>automatic drum engagement which was permanently switched off as the
>drivers could do the selection much more efficiently. The control
systems
>were very very complex and it required many hours of maintenance during
>the week to make sure it would run for the weekend. If it had been a
>private club it would never have worked but the Royal Air Force had the
>manpower to keep it maintained. Despite this many of the advanced
systems
>did not work. The winch drivers however were well trained and in the
main
>skillful so they worked round many of the minor problems. The winch was
a
>perfect example of a complex and technically advanced machine which did
>not stand up to the rigors of being operated in the real world, it was
>just too complex. Following that I flew for 7 years at a club using a
>Skylaunch. The ability to accelerate the glider was not much less than
the
>MVG but it was nowhere near as smooth. The engineering was simple, one
>could say agricultural, but that was it's main saving, there was
nothing
>complex to go wrong. The winch was made up of well tried and test
indusrty
>standard units which worked even with minimal servicing and I do mean
>minimal. The only critisism I would make is that some of the engineering
>was not agricultural enough to stand up to the abuse of club member
winch
>drivers. Bits fell off from time to time but the the winch engine,
>transmission and drums continued to work and work well.
>
>The MVG winch and the Skylaunch winch do the same job but the MVG does
it
>with much less effort. The MVG has 6 drums and it was a minor miracle if
>they were all available for use. It drank deisel like there was no
>tomorrow.
>The Skylaunch has two drums and you could purchase 2 Skylaunch winches =
4
>drums for the same amount the RAF paid for the MVG 15-20 years ago.
>
>My current club operates a Supercat winch modified by Skylaunch to take
>their engine, transmission and control. It is certainly as good as a
>standard Skylaunch and has almost no downtime. They all run on LPG.
(It's
>what passes for cheap fuel in the UK)
>With winches I believe that the KISS principle is essential
>

Yesterday, launching into a moderate headwind at Lasham on a Skylaunch
winch, we were getting better than 2000ft launches from a 1200 metre run
in K13 and K21 training gliders. The best launch in a K21 was 2500ft.

This was using 4.5mm stranded steel cable, so we might have got a couple
of hundred feet higher using lightweight synthetic cables.

There were no cable or weak link breaks, frightening incidents, or launch
failures of any sort, despite rather gusty conditions.

Derek Copeland

At 13:15 31 July 2009, Del C wrote:
>Yesterday, launching into a moderate headwind at Lasham on a Skylaunch
>winch, we were getting better than 2000ft launches from a 1200 metre run
>in K13 and K21 training gliders. The best launch in a K21 was 2500ft.
>
>This was using 4.5mm stranded steel cable, so we might have got a couple
>of hundred feet higher using lightweight synthetic cables.
>
>There were no cable or weak link breaks, frightening incidents, or
launch
>failures of any sort, despite rather gusty conditions.
>
>Derek Copeland
>
Good grief Del, give it up. I am sure the yanks are as bored of this
thread as we are.

We have the Skylaunch telemetry installed in one of our ships as a
trial, and have found it to be a very useful tool for the winch
driver. The winch cab display "lights up" at about the time of
rotation and a quick scan of the glider airspeed is very useful in
assessing the airspeed trend during the climb. It is particularly
useful as the glider begins the round out as an airspeed cue during
the reduction in line tension. The low cost makes this a very nice
innovation and we plan to install the units in our other club gliders.

Bob


On Jul 27, 1:45�pm, Derek Copeland > wrote:
> Skylaunch sell a telemetry system called 'Launch Assistant' which relays
> the actual airspeed of the glider to an LCD display mounted somewhere in
> the view of the driver. It costs a few hundred dollars in total. See:
>
> http://www.skylaunchuk.com/
>
> Derek Copeland
>
> At 16:49 27 July 2009, Chris Nicholas wrote:
>
>
>
>
>
> >At Feshiebridge, Scotland, AIUI they developed telemetry for
> >indicating glider airspeed to the winch driver, and it was said to
> >work very well. IIRC, it did not send an airspeed number in knots, but
> >rather an indication of too slow, a bit slow, OK, a bit fast, or too
> >fast (or something like that) which is what the winch driver really
> >needs to know, they believed. The unit in the glider was calibrated
> >for the glider type.
>
> >It needs somebody with first hand experience of it to tell more, and I
> >don=92t know if it has been kept going.
>
> >Chris N.- Hide quoted text -
>
> - Show quoted text -

At 18:00 31 July 2009, Jim White wrote:
>At 13:15 31 July 2009, Del C wrote:
>>Yesterday, launching into a moderate headwind at Lasham on a Skylaunch
>>winch, we were getting better than 2000ft launches from a 1200 metre
run
>>in K13 and K21 training gliders. The best launch in a K21 was 2500ft.
>>
>>This was using 4.5mm stranded steel cable, so we might have got a
couple
>>of hundred feet higher using lightweight synthetic cables.
>>
>>There were no cable or weak link breaks, frightening incidents, or
>launch
>>failures of any sort, despite rather gusty conditions.
>>
>>Derek Copeland
>>
>Good grief Del, give it up. I am sure the yanks are as bored of this
>thread as we are.
>
Just because you can't winch launch at Booker Gliding Club because of all
the helicopters and light aircraft you share Wycombe Air Park with...!

I'm only trying to convert the Colonials (and Booker pilots) to the true
faith. Why don't you move a few miles and fly at Bicester or Lasham where
they do winch launch? Bicester is almost the perfect winch launching site,
being approximately circular so that they can always launch into wind.

Del C

Some years ago, using the published statistics, I calculated the "launch
cost per hour flown", for the major and some smaller clubs. The best
value ones were Talgarth, Aboyne and Booker, all aerotow only sites. You
average more minutes per £ from an aerotow than from a winch launch.

At 04:45 01 August 2009, Derek Copeland wrote:
>At 18:00 31 July 2009, Jim White wrote:
>>At 13:15 31 July 2009, Del C wrote:
>>>Yesterday, launching into a moderate headwind at Lasham on a Skylaunch
>>>winch, we were getting better than 2000ft launches from a 1200 metre
>run
>>>in K13 and K21 training gliders. The best launch in a K21 was 2500ft.
>>>
>>>This was using 4.5mm stranded steel cable, so we might have got a
>couple
>>>of hundred feet higher using lightweight synthetic cables.
>>>
>>>There were no cable or weak link breaks, frightening incidents, or
>>launch
>>>failures of any sort, despite rather gusty conditions.
>>>
>>>Derek Copeland
>>>
>>Good grief Del, give it up. I am sure the yanks are as bored of this
>>thread as we are.
>>
>Just because you can't winch launch at Booker Gliding Club because of
all
>the helicopters and light aircraft you share Wycombe Air Park with...!
>
>I'm only trying to convert the Colonials (and Booker pilots) to the
true
>faith. Why don't you move a few miles and fly at Bicester or Lasham
where
>they do winch launch? Bicester is almost the perfect winch launching
site,
>being approximately circular so that they can always launch into wind.
>
>Del C
>

Chris Rollings wrote:
> Some years ago, using the published statistics, I calculated the "launch
> cost per hour flown", for the major and some smaller clubs. The best
> value ones were Talgarth, Aboyne and Booker, all aerotow only sites. You
> average more minutes per £ from an aerotow than from a winch launch.
>
<Related background conversation snipped...>

This stat doesn't surprise me a bit. IMHO, the key word is the "You"
beginning the ending sentence...and the implications "one" draws from it.

Aerotow/winching are completely different models, both in capital
exposure and launch pricing...not to mention fun/currency/etc.

Having logged only aerotows since ~1972, I find I'm averaging a skoshe
over 2 hours and 20 minutes per launch over 1133 tows. Pretty darned
good for an instructor, huh? (If only I were one...)

There's no doubt in my mind my per-launch flight-average would be
considerably lower had I exclusively winched, both for the reason
implicit in Chris' post, and, because there's no doubt in my mind I'd've
taken considerable snaps those days I rigged, and never aerotowed
because I thought it was dead and didn't want to spend the big (U.S.)
bux for an aerotow. How one prices their winch launches *will* have an
effect on their launch clientele's spending behaviors.

What my per-winch-launch cost might've been I'll never know...

Winching is Great Phun. I can remember one winter gaining several
thousand feet, from a 900' snap, near sunset, in a Schweizer Dragmaster
(aka 2-33). No way would I even have been out at the airfield on a day
like that had we not been winching.

Regards,
Bob - seeks to use stats wisely - W.

On Aug 2, 12:30*am, Chris Rollings > wrote:
> Some years ago, using the published statistics, I calculated the "launch
> cost per hour flown", for the major and some smaller clubs. *The best
> value ones were Talgarth, Aboyne and Booker, all aerotow only sites. *You
> average more minutes per £ from an aerotow than from a winch launch.
>
> At 04:45 01 August 2009, Derek Copeland wrote:
>
>
>
> >At 18:00 31 July 2009, Jim White wrote:
> >>At 13:15 31 July 2009, Del C wrote:
> >>>Yesterday, launching into a moderate headwind at Lasham on a Skylaunch
> >>>winch, we were getting better than 2000ft launches from a 1200 metre
> >run
> >>>in K13 and K21 training gliders. The best launch in a K21 was 2500ft.
>
> >>>This was using 4.5mm stranded steel cable, so we might have got a
> >couple
> >>>of hundred feet higher using lightweight synthetic cables.
>
> >>>There were no cable or weak link breaks, frightening incidents, or
> >>launch
> >>>failures of any sort, despite rather gusty conditions.
>
> >>>Derek Copeland *
>
> >>Good grief Del, give it up. I am sure the yanks are as bored of this
> >>thread as we are.
>
> >Just because you can't winch launch at Booker Gliding Club because of
> all
> >the helicopters and light aircraft you share Wycombe Air Park with...!
>
> >I'm only trying to convert the Colonials (and Booker pilots) to the
> true
> >faith. Why don't you move a few miles and fly at Bicester or Lasham
> where
> >they do winch launch? Bicester is almost the perfect winch launching
> site,
> >being approximately circular so that they can always launch into wind.
>
> >Del C

On Aug 2, 12:30*am, Chris Rollings > wrote:
> Some years ago, using the published statistics, I calculated the "launch
> cost per hour flown", for the major and some smaller clubs. *The best
> value ones were Talgarth, Aboyne and Booker, all aerotow only sites. *You
> average more minutes per £ from an aerotow than from a winch launch.
>

"There are three kinds of lies: lies, damned lies, and statistics."

At 06:30 02 August 2009, Chris Rollings wrote:
>Some years ago, using the published statistics, I calculated the
"launch
>cost per hour flown", for the major and some smaller clubs. The best
>value ones were Talgarth, Aboyne and Booker, all aerotow only sites.
You
>average more minutes per £ from an aerotow than from a winch launch.
>
>
A slightly unfair comparison, when you consider that two of the above
mentioned sites have ridges and wave to aid long flights and when winch
launching is used mostly for training flights.

Derek Copeland