Winch launch speed versus height gain

115 kph is about 63knots, which is close to the ideal
speed for launching a K21 (I reckon 65 knots), which
I guess equals the best L/D speed allowing for the
extra wing loading caused by the cable pull. Any faster
or slower than this will give a less high launch as
the glider is flying less efficiently. 90 kph is pretty
close to the loaded stall speed.

Del Copeland

At 22:24 01 November 2007, Andreas Maurer wrote:

Definitely not with our 280 hp Turbo Diesel winch and
an ASK-21.

90 kp/h gets about 350 meters, 115 kp/h gets over 400
meters.



Bye
Andreas

On 1 Nov., 18:39, "Neil" wrote:
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to my
gliders placarding, will I get higher or lower than a lower speed launch?
I used to consider faster meant higher, but last weekend a most experienced
colleague said you'd end less high, as you spend less time gaining height.
I'm sure there's a set of graphs that would show a polar curve type
trade-off, but is there a simple way of looking at this?

Neil

I have done about 350 winch launches this year and have experienced
that higher launch speeds tend to get more height. In particular I was
surprised by a few launches which were far to fast (beyond the allowed
launch speed) which resulted in a noticeable increase in launch
altitude. I always believed in the "you'd end less high, as you spend
less time gaining height" approach but I might have to rethink this.
I guess it also depends on the glider as a heavy glass ship kann
effectively convert excess speed into height after releasing.

I also believe that you can often trade off a few feet of height gain
for a safer launch;-)

At the risk of stating the obvious, assuming that the
winch/cable angle at the top of the winch launch is
a constant, then the height gained by the top of the
launch is simply related to the length of cable left
unwound.

You can work out the effects of different wind speeds,
glider climb angles, cable pulling in speeds etc but,
in the end, the highest possible launch will always
result from a steep climb at a high glider airspeed
but with a low cable speed. That scenario requires
a significant headwind and a winch that is capable
of pulling with sufficiently powerful, but also controllable,
torque at the required, lowish, cable speed.

John Galloway






On 1 Nov., 18:39, 'Neil' wrote:
Ok, I could probably arrange with the winch driver
to experiment, but is
there any definitive guidance on getting the greatest
height off a winch
launch? (eg. Skylaunch).

i.e. if I'm 'driven' at the higher end of the speed
range acceptable to my
gliders placarding, will I get higher or lower than
a lower speed launch?
I used to consider faster meant higher, but last weekend
a most experienced
colleague said you'd end less high, as you spend less
time gaining height.
I'm sure there's a set of graphs that would show a
polar curve type
trade-off, but is there a simple way of looking at
this?

Neil

At high enough wind speeds, the maximum altitude is actually achievable by
letting cable out, rather than winching it in.

Mike Schumann

"John Galloway" wrote in message
...
At the risk of stating the obvious, assuming that the
winch/cable angle at the top of the winch launch is
a constant, then the height gained by the top of the
launch is simply related to the length of cable left
unwound.

You can work out the effects of different wind speeds,
glider climb angles, cable pulling in speeds etc but,
in the end, the highest possible launch will always
result from a steep climb at a high glider airspeed
but with a low cable speed. That scenario requires
a significant headwind and a winch that is capable
of pulling with sufficiently powerful, but also controllable,
torque at the required, lowish, cable speed.

John Galloway






On 1 Nov., 18:39, 'Neil' wrote:
Ok, I could probably arrange with the winch driver
to experiment, but is
there any definitive guidance on getting the greatest
height off a winch
launch? (eg. Skylaunch).

i.e. if I'm 'driven' at the higher end of the speed
range acceptable to my
gliders placarding, will I get higher or lower than
a lower speed launch?
I used to consider faster meant higher, but last weekend
a most experienced
colleague said you'd end less high, as you spend less
time gaining height.
I'm sure there's a set of graphs that would show a
polar curve type
trade-off, but is there a simple way of looking at
this?

Neil







--
Posted via a free Usenet account from http://www.teranews.com

As I have never winch launched I would like to know.
At which 'point" do you let the cable out and what would be the wind
speed to carry the extra load of the cable and still climb.
Would it be, wind speed = glider stall speed, plus safety margin,
plus some extra speed to carry the cable and cable drag, hence 55m/h
would be the wind speed for a 15 meter class glider. Could the wind
speed be less and still climb?
An other question.
In the early launch phase would the winch have to generate at least
the load that corresponds to the lifting force for a given speed of
that glider, plus the winding-in speed of the cable to sustained
flight?
If it is windy the take-up speed of the cable is less but the load is
it still the same is that assumption correct?
Udo


On Nov 6, 9:25 am, "Mike Schumann"
wrote:
At high enough wind speeds, the maximum altitude is actually achievable by
letting cable out, rather than winching it in.

Mike Schumann

"John Galloway" wrote in message

...





At the risk of stating the obvious, assuming that the
winch/cable angle at the top of the winch launch is
a constant, then the height gained by the top of the
launch is simply related to the length of cable left
unwound.

You can work out the effects of different wind speeds,
glider climb angles, cable pulling in speeds etc but,
in the end, the highest possible launch will always
result from a steep climb at a high glider airspeed
but with a low cable speed. That scenario requires
a significant headwind and a winch that is capable
of pulling with sufficiently powerful, but also controllable,
torque at the required, lowish, cable speed.

John Galloway

Mike,

That is 'kiting' and is a whole different ball game
that can only work in very strong winds. In 30 years
at a club doing 8000 winch launches a year I have never
witnessed it - although the even-older-than-me members
tell tales of it. The main disincentive at our site
is the risk of excessive lengths of cable being blown
over power lines, trees or structures before it can
be reeled in.

John


At 14:30 06 November 2007, Mike Schumann wrote:
At high enough wind speeds, the maximum altitude is
actually achievable by
letting cable out, rather than winching it in.

Mike Schumann

'John Galloway' wrote in message
...
At the risk of stating the obvious, assuming that
the
winch/cable angle at the top of the winch launch is
a constant, then the height gained by the top of the
launch is simply related to the length of cable left
unwound.

You can work out the effects of different wind speeds,
glider climb angles, cable pulling in speeds etc but,
in the end, the highest possible launch will always
result from a steep climb at a high glider airspeed
but with a low cable speed. That scenario requires
a significant headwind and a winch that is capable
of pulling with sufficiently powerful, but also controllable,
torque at the required, lowish, cable speed.

John Galloway






On 1 Nov., 18:39, 'Neil' wrote:
Ok, I could probably arrange with the winch driver
to experiment, but is
there any definitive guidance on getting the greatest
height off a winch
launch? (eg. Skylaunch).

i.e. if I'm 'driven' at the higher end of the speed
range acceptable to my
gliders placarding, will I get higher or lower than
a lower speed launch?
I used to consider faster meant higher, but last weekend
a most experienced
colleague said you'd end less high, as you spend less
time gaining height.
I'm sure there's a set of graphs that would show a
polar curve type
trade-off, but is there a simple way of looking at
this?

Neil







--
Posted via a free Usenet account from http://www.teranews.com

"Udo" wrote in message
ups.com...
As I have never winch launched I would like to know.
At which 'point" do you let the cable out and what would be the wind
speed to carry the extra load of the cable and still climb.
Would it be, wind speed = glider stall speed, plus safety margin,
plus some extra speed to carry the cable and cable drag, hence 55m/h
would be the wind speed for a 15 meter class glider. Could the wind
speed be less and still climb?
An other question.
In the early launch phase would the winch have to generate at least
the load that corresponds to the lifting force for a given speed of
that glider, plus the winding-in speed of the cable to sustained
flight?
If it is windy the take-up speed of the cable is less but the load is
it still the same is that assumption correct?
Udo

It could work like this. Obviously, the wind has to be very strong aloft
for it to work.

The pilot is mid-launch on a very windy day and he's on the radio yelling
for less speed from the winch. The winch driver slows down the drum but the
pilot keeps asking for less speed - it seems there is a strong wind layer
aloft.

Eventually, as the winch driver keeps slowing the drum it comes to a
complete stop yet the pilot is still asking for less speed. The winch
driver shrugs, puts the winch in reverse and starts paying out cable. The
pilot hangs on to the cable since he sees he is still climbing. This can
continue until the winch runs out of cable - which, hopefully, is well
attached to the drum.

The trick is for the winch driver to maintain a constant tension on the
cable and for the pilot not to release just because he has reached the usual
release height. In fact, if the winch computer controls the cable tension
automatically, the winch may reverse without driver intervention.

Bill Daniels

I didn't mean to imply that this is something that you would ever encounter
during normal operations. This was just a theoretical exercise to show the
effect of extreme headwinds on optimal cable speed.

Mike Schumann

"John Galloway" wrote in message
...
Mike,

That is 'kiting' and is a whole different ball game
that can only work in very strong winds. In 30 years
at a club doing 8000 winch launches a year I have never
witnessed it - although the even-older-than-me members
tell tales of it. The main disincentive at our site
is the risk of excessive lengths of cable being blown
over power lines, trees or structures before it can
be reeled in.

John


At 14:30 06 November 2007, Mike Schumann wrote:
At high enough wind speeds, the maximum altitude is
actually achievable by
letting cable out, rather than winching it in.

Mike Schumann

'John Galloway' wrote in message
...
At the risk of stating the obvious, assuming that
the
winch/cable angle at the top of the winch launch is
a constant, then the height gained by the top of the
launch is simply related to the length of cable left
unwound.

You can work out the effects of different wind speeds,
glider climb angles, cable pulling in speeds etc but,
in the end, the highest possible launch will always
result from a steep climb at a high glider airspeed
but with a low cable speed. That scenario requires
a significant headwind and a winch that is capable
of pulling with sufficiently powerful, but also controllable,
torque at the required, lowish, cable speed.

John Galloway






On 1 Nov., 18:39, 'Neil' wrote:
Ok, I could probably arrange with the winch driver
to experiment, but is
there any definitive guidance on getting the greatest
height off a winch
launch? (eg. Skylaunch).

i.e. if I'm 'driven' at the higher end of the speed
range acceptable to my
gliders placarding, will I get higher or lower than
a lower speed launch?
I used to consider faster meant higher, but last weekend
a most experienced
colleague said you'd end less high, as you spend less
time gaining height.
I'm sure there's a set of graphs that would show a
polar curve type
trade-off, but is there a simple way of looking at
this?

Neil







--
Posted via a free Usenet account from http://www.teranews.com







--
Posted via a free Usenet account from http://www.teranews.com

John Galloway wrote:

That is 'kiting' and is a whole different ball game
that can only work in very strong winds.

You also need a winch that can reverse. We have a Supacat that I'm told
would be damaged it you tried to reverse it.

I can put numbers on the wind speed needed for kiting. The only time
I've seen the Supacat stop during a launch. It was Dec 31, 2000, a very
windy day with 3 inches of snow on the field. We were flying the ASK-21.
Wind speed at the top of the launch was 50 kts - I trimmed to 50 and was
stationary above the field. The winch stopped almost as soon as the K21
rotated into a full climb. It climbed out at 80 kts - the only time I've
ever seen a K21 reach Vwinch.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Kiting:
=20
I have never kited anyone on our winch. I do wonder whether it would be nec=
essary to take the winch out of gear in order to pay out the cable and what=
effect that would have on the pilot.
=20
I imaging a series of payouts with the glider lowering the nose during the =
procedure, followed by take-in sessions, and finally some swearing when the=
winch driver realises that he has now lost control of a very long length o=
f cable.
=20
For a glider with stall speed 40 kts and optimum winch speed ?1.5 x stall s=
peed =3D 60 knots.
If the cable is hanging down 45 degrees below the horizon, and the glider i=
s pointing 40 degrees above the horizon, then I anticipate an upper level w=
ind speed of about 45 kts+ is needed for kiting.
=20
I think we launch fine up to about 20 kts ground wind speed. I have launche=
d in 25kts but the instructors are starting to put the toys away, and I thi=
nk we have stopped launching at 30 kts. So not too much wind gradient need=
ed, but it does require the pilot and winch driver not to break the weak li=
nk on the initial climb.
=20
Imagine reacting rapidly to a broken weak link when pointed skywards at 100=
ft, with a 30 kt headwind!
=20
Rory
=20
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