SAFE Winch Launching

At 21:00 19 July 2009, Don Johnstone wrote:
At 20:00 19 July 2009, Del C wrote:
On a very still day the gliders up to DG1000Ts were being accelerated
by
the Skylaunch winch from zero to lift off speed (50-60mph) in about 3
seconds, which is little slower than Bill claims for his US superwinch.
Any faster than this can be dangerous for some types of glider, because
it
can cause excessive pitch up rates. Excessive acceleration can also
bang
down the tails of those gliders that set on their nose wheels or skids
pretty hard onto the ground, with a risk of structural damage!

Derek Copeland

Not if you hold the tail down to prevent that happening. In theory the
faster the acceleration to flying speed the safer the launch, having
effective controls makes all the difference. Being towed down the field
on
the ground accelerating slowly is a recipe for disaster.

Whilst I agree with Don that the ground run acceleration should be
reasonably brisk to give quick aileron control, if it is too rapid some
types of gliders pitch up dangerously quickly, due to the rotational
couple between the cable pull line to the belly hook and the centre of
gravity. This risks a flick spin on rotation, or making recovery from a
low launch failure almost impossible.

This doesn't affect Grob G103s, which I believe is the type Don instructs
in, due to its weight (it's not nicknamed the concrete swan for nothing),
low set wings and hence low centre of gravity, but it does affect lighter
high winged gliders such as the K6 or K8.

We do hold the tail down for some of the more delicate vintage types, but
we often don't have enough helpers at the launch point to do this
additional task on a routine basis. OK if you have lots of ATC Cadets
hanging around with nothing much else to do!

Derek Copeland

On Jul 19, 1:18*pm, johngalloway wrote:
On 19 July, 16:54, bildan wrote:

On Jul 19, 4:30*am, Derek Copeland wrote:

Just to emphasize John's point about a properly set up automatic gearbox
giving smooth and imperceptible gear changes during a winch launch, see if
you can hear the gearchanges in this video of a new Skylaunch winch in
action at Lasham?

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

Derek Copeland

Opening the throttle like a little old lady will mask shifts on any
transmission. *This obviously depends a great deal on the winch
operator opening the throttle very gingerly.

Bill,

You are implying that if the throttle of a Skylaunch winch is advanced
rapidly then the autobox changes will become obvious or a problem or
whatever. *This is simply not the case.

At various times I have test driven a Skylaunch, been inside and
outside the winch looking out for gear changes (because this was
something I was initially wondering about too), and been launched. *I
have seen the throttle advanced rapidly to maximum or advanced slowly
over 3 seconds and it makes no difference to appreciation of
gearchanges. *As a personal example I had a launch recently in which
the driver (watched by a friend in the cab) for some reason pushed the
throttle rapidly through the throttle stop guide for my type and gave
me a very overpowered initial acceleration. *There was absolutely no
detectable gear change effect during the initial (very rapid)
acceleration.

John Galloway

I am very familiar with many old Gerhlein winches that use exactly the
same engine and transmission as the Skylaunch - there is essentially
no difference. Unfortunately, I'm also VERY familiar with the General
Motors TH400 transmission used in the Skylaunch as a consequence of
the old Gerhleins.

Anyone can confirm everything I write below by calling a transmission
shop - or reading a shop technical manual. In my circle it's
considered common knowledge but since this is for the Brits, it's a
long post.

To get some data I borrowed a neighbor's GM Surburban with the view to
videotaping a portable repair shop electronic vehicle scanner display
which shows the shifts. The Surburban uses the same engine and
transmission as the Skylaunch. Unfortunately, the camera couldn't
read the LCD display with the lighting available. I plan to try again
tomorrow with different lighting. I'll post the video on YouTube.

To insure constant throttle, I monitored the throttle position sensor
with the scanner. At 24% throttle, the transmission made the 1-2 &
2-3 up-shifts at 11 and 23 MPH which is normal. On level ground and
with a lightly loaded vehicle, these shifts are VERY smooth and could
easily have been missed without the scanner. Using low power can mask
shifts. Not hearing or feeling them doesn't mean they don't happen or
they don't matter - please continue reading.

The old hydraulic transmissions like the TH400 don't have any "smarts"
other than what the GM engineers designed into them. They just do
what they do. Non-electronic automatic transmissions from all
manufacturers work(ed) essentially the same. Which is not to say they
worked well since we now have electronically controlled transmissions
which work much better.

I selected a stretch of high mountain road (9000 feet elev) with a
level section leading to a moderate hill with an equal descent on the
other side to simulate a glider hitting first a thermal and then sink
during a winch launch.

Holding fixed throttle (not speed), the transmission unlocked the
torque converter clutch just as the vehicle encountered the uphill
grade seen as a jump from 1700 RPM to 2000 RPM. This is effectively a
23% downshift since the torque converter is now slipping and
multiplying torque.

As the vehicle continued up the hill, the transmission shifted out of
overdrive into 3rd gear shown by a 1300 RPM increase in RPM. Finally,
near the top of the hill, the transmission downshifted to 2nd and a
further 1800 RPM increase. The 3-2 down shift is what most people
call "passing gear".

As the vehicle topped the hill and started down, the transmission
quickly up-shifted reversing its actions on the uphill grade.

The transmission was doing exactly what it was designed to do which is
to assist the driver in maintaining speed on a hilly road by changing
gear ratios to keep engine RPM in the power band. Each downshift
increases torque multipication which, in a winch, would be seen as
increasing rope tension. Each up-shift decreases torque multipication
which, in a winch, would be seen as decreasing rope tension - assuming
a fixed throttle.

In a winch, the transmission would see the increasing rope tension
caused by a glider encountering a thermal as a hill and start
downshifting increasing the tension further. This would INCREASE rope
tension in thermals. If the glider hit sink the slackening tension
would be seen as a downhill grade and it would up-shift and DECREASE
rope tension - exactly the opposite of what is needed for a smooth,
safe launch which is to hold tension constant.

That's why I think it is very poor engineering practice to use an
automobile transmission in a glider winch. It's designed to work in
an entirely different universe. The ONLY credible reason to insist on
using one in a glider winch is their low cost and availability. The
Hydrowinch people in Colorado Springs were able to build a
computerized diesel/hydrostatic tension controlled winch for LESS than
the selling price of a Skylaunch.

If people still insist on using automatic transmissions, there are two
or three modifications that can make them less bad. The first is a
"Manual Valve Body" which allows the operator to choose a gear and the
transmission will stay there regardless. This is NOT the same as
putting the gear selector in "2" since the 1-2 up-shift still occurs
in that case. Only the MVB actually prevents automatic shifting.
Unlike getting a heavy Surburban rolling, there is no need for lower
gears when launching a glider so the transmission can be put in
whatever gear is needed for the main part of the launch.

The second modification is to control the torque converter clutch. It
should lock up the torque converter - preventing torque multipication
- just after the throttle advance starts and not unlock until the
throttle is returned to idle.

An MVB opens the door to a third modification which is to replace the
stock gears with extremely close ratio planetary gear sets. These
allow the operator to choose small changes in winch gearing to suit a
range of wind and density altitude conditions.

TH400's can be ordered on-line with all three modifications already
installed for only 3-400 hundred USD more than a stock transmission.
If you're building a winch with an automatic, that would be money well
spent.

If you disagree call a transmission shop - preferably one that deals
with drag racers - and get the facts.

bildan wrote:
On Jul 19, 4:30 am, Derek Copeland wrote:
Just to emphasize John's point about a properly set up automatic gearbox
giving smooth and imperceptible gear changes during a winch launch, see if
you can hear the gearchanges in this video of a new Skylaunch winch in
action at Lasham?

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

Derek Copeland

Opening the throttle like a little old lady will mask shifts on any
transmission. This obviously depends a great deal on the winch
operator opening the throttle very gingerly.

It's one of the things that attracts a certain kind of person to
soaring. It's called skill, and developing it as a winch driver is as
rewarding as being on the other end of the string. (though I still
prefer being winched, rather than winching)

The "job well done" feeling after a shift on the winch is one of the
rewards that the whiners, and dumb downers miss completely.

Is it desirable to have a powerful, smooth controllable winch -
Definitely. Is it neccessary for safety and operations to have the
perfect winch? I can't say because we can't even agree on what is
desirable beyond that is should be powerful enough, smooth enough and
controllable enough. And the "enough" part is pretty debatable.

FWIW the universal standard on winches seems to be zero to full power
(for the situation) in 3 to 4 seconds - with the focus on smoothly
increasing power so as to prevent uncontrollable acceleration in the
glider.

Our Tost winches were originally fitted with Powerglide gearboxes that were
locked in top gear as a Tost modification.

A trial was carried out about 4 years ago by fitting one of them with a
very slightly modified, 3 speed, shifting TH400 gearbox supplied by
Skylaunch, which we found gave no problems at all and had several
advantages, in that it can safely be run backwards (as long as you leave
the engine running to give oil pressure) which we needed for retrieve
winching, better acceleration for the heavier gliders, and less gearbox
oil over-heating. As a result of this trial, both of our Tosts were so
fitted. The overall gearing was such that the upshift gear changes occured
during the ground run and the main part of the launch is done in top gear.
The same applies to our new Skylaunch winches.

In August 2008 our club hired a 'pre-owned' Skylaunch winch and ran that
for an extended trial period. Compared with the Tosts we found it to be
very easy to drive and to give smooth, nicely speeded launches, with non
of the problems suggested by Bill! As a result of this trial the club
commitee decided to buy two of them, and to sell one of the Tosts, which
we have already done. We still have one as a back up, but it hasn't come
out of the MT hangar for months. If a club is looking for a half decent
secondhand winch, perhaps they should make an offer to Lasham? If it was
fitted with the Skylaunch throttle system it would be three-quarters
decent.

In answer to Bill Daniel's other point, you can bang open the throttles
of the above winches, or of our new Skylaunches by over-riding the
throttle dampers, as fast as you want without causing harsh gear changes,
but then you over-accelerate the gliders, and bang the tails down for nose
sitting gliders, such as K13s, Grob G103 and K21s, too hard with a risk of
structural damage. Again that's due to that pesky belly hook to c of g
rotational couple!

Comparing a Gerhlein winch to a Skylaunch is somewhat like comparing a
Ford Model T to their latest models. Similar basic components but
developed over many years.

I believe the Hydrostart winch, on which the Hydrowinch is based would
cost something like 500,000 Euros with all new components, compared with
about 90,000 Euros for an all new Skylaunch 2 in Europe. Shipping costs
and import duties make it more expensive in the States, so it might be
worth making them under license over there. All of the development work
has already been done.

Derek Copeland


At 01:40 20 July 2009, bildan wrote:
On Jul 19, 1:18=A0pm, johngalloway wrote:
On 19 July, 16:54, bildan wrote:

On Jul 19, 4:30=A0am, Derek Copeland wrote:

Just to emphasize John's point about a properly set up automatic
gear=
box
giving smooth and imperceptible gear changes during a winch
launch,
s=
ee if
you can hear the gearchanges in this video of a new Skylaunch
winch
i=
n
action at Lasham?

http://www.youtube.com/watch?v=3DriqhzcXZqzg

Derek Copeland

Opening the throttle like a little old lady will mask shifts on any
transmission. =A0This obviously depends a great deal on the winch
operator opening the throttle very gingerly.

Bill,

You are implying that if the throttle of a Skylaunch winch is advanced
rapidly then the autobox changes will become obvious or a problem or
whatever. =A0This is simply not the case.

At various times I have test driven a Skylaunch, been inside and
outside the winch looking out for gear changes (because this was
something I was initially wondering about too), and been launched.
=A0I
have seen the throttle advanced rapidly to maximum or advanced slowly
over 3 seconds and it makes no difference to appreciation of
gearchanges. =A0As a personal example I had a launch recently in which
the driver (watched by a friend in the cab) for some reason pushed the
throttle rapidly through the throttle stop guide for my type and gave
me a very overpowered initial acceleration. =A0There was absolutely no
detectable gear change effect during the initial (very rapid)
acceleration.

John Galloway

I am very familiar with many old Gerhlein winches that use exactly the
same engine and transmission as the Skylaunch - there is essentially
no difference. Unfortunately, I'm also VERY familiar with the General
Motors TH400 transmission used in the Skylaunch as a consequence of
the old Gerhleins.

Anyone can confirm everything I write below by calling a transmission
shop - or reading a shop technical manual. In my circle it's
considered common knowledge but since this is for the Brits, it's a
long post.

To get some data I borrowed a neighbor's GM Surburban with the view to
videotaping a portable repair shop electronic vehicle scanner display
which shows the shifts. The Surburban uses the same engine and
transmission as the Skylaunch. Unfortunately, the camera couldn't
read the LCD display with the lighting available. I plan to try again
tomorrow with different lighting. I'll post the video on YouTube.

To insure constant throttle, I monitored the throttle position sensor
with the scanner. At 24% throttle, the transmission made the 1-2 &
2-3 up-shifts at 11 and 23 MPH which is normal. On level ground and
with a lightly loaded vehicle, these shifts are VERY smooth and could
easily have been missed without the scanner. Using low power can mask
shifts. Not hearing or feeling them doesn't mean they don't happen or
they don't matter - please continue reading.

The old hydraulic transmissions like the TH400 don't have any
"smarts"
other than what the GM engineers designed into them. They just do
what they do. Non-electronic automatic transmissions from all
manufacturers work(ed) essentially the same. Which is not to say they
worked well since we now have electronically controlled transmissions
which work much better.

I selected a stretch of high mountain road (9000 feet elev) with a
level section leading to a moderate hill with an equal descent on the
other side to simulate a glider hitting first a thermal and then sink
during a winch launch.

Holding fixed throttle (not speed), the transmission unlocked the
torque converter clutch just as the vehicle encountered the uphill
grade seen as a jump from 1700 RPM to 2000 RPM. This is effectively a
23% downshift since the torque converter is now slipping and
multiplying torque.

As the vehicle continued up the hill, the transmission shifted out of
overdrive into 3rd gear shown by a 1300 RPM increase in RPM. Finally,
near the top of the hill, the transmission downshifted to 2nd and a
further 1800 RPM increase. The 3-2 down shift is what most people
call "passing gear".

As the vehicle topped the hill and started down, the transmission
quickly up-shifted reversing its actions on the uphill grade.

The transmission was doing exactly what it was designed to do which is
to assist the driver in maintaining speed on a hilly road by changing
gear ratios to keep engine RPM in the power band. Each downshift
increases torque multipication which, in a winch, would be seen as
increasing rope tension. Each up-shift decreases torque multipication
which, in a winch, would be seen as decreasing rope tension - assuming
a fixed throttle.

In a winch, the transmission would see the increasing rope tension
caused by a glider encountering a thermal as a hill and start
downshifting increasing the tension further. This would INCREASE rope
tension in thermals. If the glider hit sink the slackening tension
would be seen as a downhill grade and it would up-shift and DECREASE
rope tension - exactly the opposite of what is needed for a smooth,
safe launch which is to hold tension constant.

That's why I think it is very poor engineering practice to use an
automobile transmission in a glider winch. It's designed to work in
an entirely different universe. The ONLY credible reason to insist on
using one in a glider winch is their low cost and availability. The
Hydrowinch people in Colorado Springs were able to build a
computerized diesel/hydrostatic tension controlled winch for LESS than
the selling price of a Skylaunch.

If people still insist on using automatic transmissions, there are two
or three modifications that can make them less bad. The first is a
"Manual Valve Body" which allows the operator to choose a gear and the
transmission will stay there regardless. This is NOT the same as
putting the gear selector in "2" since the 1-2 up-shift still occurs
in that case. Only the MVB actually prevents automatic shifting.
Unlike getting a heavy Surburban rolling, there is no need for lower
gears when launching a glider so the transmission can be put in
whatever gear is needed for the main part of the launch.

The second modification is to control the torque converter clutch. It
should lock up the torque converter - preventing torque multipication
- just after the throttle advance starts and not unlock until the
throttle is returned to idle.

An MVB opens the door to a third modification which is to replace the
stock gears with extremely close ratio planetary gear sets. These
allow the operator to choose small changes in winch gearing to suit a
range of wind and density altitude conditions.

TH400's can be ordered on-line with all three modifications already
installed for only 3-400 hundred USD more than a stock transmission.
If you're building a winch with an automatic, that would be money well
spent.

If you disagree call a transmission shop - preferably one that deals
with drag racers - and get the facts.

OK Bill so would you confirm that:

1. You have never seen a skylaunch winch
2. Therefore you have never driven a Skylaunch winch
3. Therefore you have never seen a launch carried out by a Skylaunch
winch
4 In fact the closest you have ever been to a Skylaunch winch is over 5000
miles.
Hardly makes you particularly knowledgeable about Skylaunch winches does
it?

I have no comment to make concerning the operation or construction of any
winch made in the USA, I am sure they are adequate. My only suggestion is
that a "tension controlled" winch is about the craziest idea I have ever
heard, not least because, thankfully, it would never work.

Don,

Bill should have seen plenty of videos of Skylaunch winches in action
(I've made quite a few), all of which show nice well controlled launches.
The dodgy lauches are all on Tosts or homebuilds.

Constant Tension winches might just work, as it not too dissimilar in
principle to Constant Torque, which has been used before, but this is
still unproven. My worry about it is that it can be affected by what the
glider pilot does at the other end of a long and slightly elastic cable.

I don't know why Bill has to keep attacking Skylaunch, who are well
regarded in European gliding circles and produce a good solid product.
Maybe he regards them as a threat to his potential US winch building
empire! I should point out to him that most winch manufacturing in Europe
is done as a sideline to other engineering activities by gliding
enthusiasts; this includes Skylaunch.

Derek Copeland

At 10:15 20 July 2009, Don Johnstone wrote:
OK Bill so would you confirm that:

1. You have never seen a skylaunch winch
2. Therefore you have never driven a Skylaunch winch
3. Therefore you have never seen a launch carried out by a Skylaunch
winch
4 In fact the closest you have ever been to a Skylaunch winch is over
5000
miles.
Hardly makes you particularly knowledgeable about Skylaunch winches does
it?

I have no comment to make concerning the operation or construction of
any
winch made in the USA, I am sure they are adequate. My only suggestion
is
that a "tension controlled" winch is about the craziest idea I have
ever
heard, not least because, thankfully, it would never work.

At 21:45 19 July 2009, Del C wrote:

Whilst I agree with Don that the ground run acceleration should be
reasonably brisk to give quick aileron control, if it is too rapid some
types of gliders pitch up dangerously quickly, due to the rotational
couple between the cable pull line to the belly hook and the centre of
gravity. This risks a flick spin on rotation, or making recovery from a
low launch failure almost impossible.

This doesn't affect Grob G103s, which I believe is the type Don
instructs
in, due to its weight (it's not nicknamed the concrete swan for
nothing),
low set wings and hence low centre of gravity, but it does affect
lighter
high winged gliders such as the K6 or K8.

We do hold the tail down for some of the more delicate vintage types,
but
we often don't have enough helpers at the launch point to do this
additional task on a routine basis. OK if you have lots of ATC Cadets
hanging around with nothing much else to do!


There really is no conflict here, the gliders that are likely to suffer
from to brisk acceleration are generally lighter and high winged. The have
an advantage on two fronts in that there is less inertia to overcome so
they do not need the "extra" power to accelerate and of course being
high winged a wing drop is less likely to result in the wing touching the
ground. They can therefore be launched safely with less initial power.
On the other hand, modern glass gliders tend to be heavier and do need the
extra power to accelerate quickly but once this acceleration phase is over
they actually need less power to move them through the air so the throttle
technique needs to be different and this is where knowing what glider you
are launching is important.
On a Skylaunch I find that with wooden gliders and some lighter glass
gliders the throttle needs to be advanced to the adjustable stop. With
heavy 2 seaters the throttle needs go go through the stop and then return
as soon as the glider is moving. The "extra" power is only needed to
overcome the inertia. Many drivers to not provide enough power quick
enough for heavier gliders, maybe because of the caution needed for
lighter ones and not being taught to recognise the difference. The pilot
needs to play his part and establish a positive rate of climb to prevent
overspeed.
As far as holding the tail down, I would have thought this preferable to
having to accept a slower acceleration with the attendant risk of wing
drop/yaw.
We did not hold down the tail of Grob 103s, we did the Janus.
The concrete swan was actually the Astir Del :-)

When launching heavy glass two seaters such as the K21 or DG1000 on a
Skylaunch I just put the power setting in A or A+ depending on type and
advance the throttle to the preset stop as quickly as it will allow me to.
Only if the glider fails to take off within about 4 seconds would I push
the throttle through the spring loaded stop.

You have to be a little bit more gentle with the earlier versions of the
Grob Twin Astir and G103 because they only launch on red weak links. I
think that any type of Grob two-seater has the 'concrete swan' nickname,
even though it was originally applied to the Twin Astir.

For lighter gliders such as the K13 I use a lower power setting and
advance the throttle to the preset stop over a count of 3. This is only to
give a slightly more gentle and progressive acceleration and not to bang
their tails on the ground too hard.

Derek Copeland

At 11:15 20 July 2009, Don Johnstone wrote:
At 21:45 19 July 2009, Del C wrote:

Whilst I agree with Don that the ground run acceleration should be
reasonably brisk to give quick aileron control, if it is too rapid some
types of gliders pitch up dangerously quickly, due to the rotational
couple between the cable pull line to the belly hook and the centre of
gravity. This risks a flick spin on rotation, or making recovery from a
low launch failure almost impossible.

This doesn't affect Grob G103s, which I believe is the type Don
instructs
in, due to its weight (it's not nicknamed the concrete swan for
nothing),
low set wings and hence low centre of gravity, but it does affect
lighter
high winged gliders such as the K6 or K8.

We do hold the tail down for some of the more delicate vintage types,
but
we often don't have enough helpers at the launch point to do this
additional task on a routine basis. OK if you have lots of ATC Cadets
hanging around with nothing much else to do!


There really is no conflict here, the gliders that are likely to suffer
from to brisk acceleration are generally lighter and high winged. The
have
an advantage on two fronts in that there is less inertia to overcome so
they do not need the "extra" power to accelerate and of course being
high winged a wing drop is less likely to result in the wing touching
the
ground. They can therefore be launched safely with less initial power.
On the other hand, modern glass gliders tend to be heavier and do need
the
extra power to accelerate quickly but once this acceleration phase is
over
they actually need less power to move them through the air so the
throttle
technique needs to be different and this is where knowing what glider
you
are launching is important.
On a Skylaunch I find that with wooden gliders and some lighter glass
gliders the throttle needs to be advanced to the adjustable stop. With
heavy 2 seaters the throttle needs go go through the stop and then
return
as soon as the glider is moving. The "extra" power is only needed to
overcome the inertia. Many drivers to not provide enough power quick
enough for heavier gliders, maybe because of the caution needed for
lighter ones and not being taught to recognise the difference. The pilot
needs to play his part and establish a positive rate of climb to prevent
overspeed.
As far as holding the tail down, I would have thought this preferable to
having to accept a slower acceleration with the attendant risk of wing
drop/yaw.
We did not hold down the tail of Grob 103s, we did the Janus.
The concrete swan was actually the Astir Del :-)

Derek Copeland wrote:
....
In answer to Bill Daniel's other point, you can bang open the throttles
of the above winches, or of our new Skylaunches by over-riding the
throttle dampers, as fast as you want without causing harsh gear changes,
but then you over-accelerate the gliders, and bang the tails down for nose
sitting gliders, such as K13s, Grob G103 and K21s, too hard with a risk of
structural damage. Again that's due to that pesky belly hook to c of g
rotational couple!...
Derek Copeland

There is another factor worth considering in the matter of launches.

An automatic gearbox / transmission is intended to transfer as much
horse power as possible from engine to axle.

Maximizing HP in this way involves a LARGE torque at slow speed,
tapering to a low torque at high speed.

You have mentioned that the objective of a glider launch is holding the
tension constant. This is a different objective altogether!
This calls for a ramped HP, so that either a ramped throttle application
to achieve flight speed is needed, at which point that HP is held - or
as a possible alternative: running an engine at constant (max) HP, but
throwing away excess power during the ramp to flight speed.

Brian W

Don Johnstone wrote:
... a "tension controlled" winch is about the craziest idea I have ever
heard, not least because, thankfully, it would never work.

Why not?

Brian W