Almost perfect payout winch launch.

In article ,
Tony wrote:



If you're using a pulley why not just have a release on the tow vehicle?

Hi Tony,

I was unclear about the pulley launch. The pulley is on the tow vehicle.
One end of the line is anchored, the line goes over the pulley to the
glider. The tow vehicle is pulling from the middle of the rope, going in
the same direction as the glider. The advantages are that acceleration
at the glider is almost as fast as a winch launch and the tow car only
has to go 25-30 mph maximum to launch the glider. No gear changes
required, and the low vehicle speed means it can be done on less than
paved surfaces. Launching with 4000 feet of dacron rope and an old LTD
with 500 lbs of bricks in the trunk used to get our Ka-8 to 2000' if we
had a bit of headwind.

A release can be put at the anchor point, but that's a long way from
where the action is.

There are some other disadvantages to this type of ground launch as
well. Turn around time is fairly long. Switching ends of the rope after
each launch can speed things up especially if the anchor point is
another vehicle. Rope recovery can be problematic since a chute is
usually not part of the rope end hardware, so the rope tends to fall a
ways downwind.

On Monday, May 20, 2013 9:52:58 AM UTC-5, WB wrote:
In article , Tony wrote: If you're using a pulley why not just have a release on the tow vehicle? Hi Tony, I was unclear about the pulley launch. The pulley is on the tow vehicle. One end of the line is anchored, the line goes over the pulley to the glider. The tow vehicle is pulling from the middle of the rope, going in the same direction as the glider. The advantages are that acceleration at the glider is almost as fast as a winch launch and the tow car only has to go 25-30 mph maximum to launch the glider. No gear changes required, and the low vehicle speed means it can be done on less than paved surfaces. Launching with 4000 feet of dacron rope and an old LTD with 500 lbs of bricks in the trunk used to get our Ka-8 to 2000' if we had a bit of headwind. A release can be put at the anchor point, but that's a long way from where the action is. There are some other disadvantages to this type of ground launch as well. Turn around time is fairly long. Switching ends of the rope after each launch can speed things up especially if the anchor point is another vehicle. Rope recovery can be problematic since a chute is usually not part of the rope end hardware, so the rope tends to fall a ways downwind.

ah i see, i was thinking of a fixed pulley.

On Monday, May 20, 2013 11:00:54 AM UTC-4, Tony wrote:
On Monday, May 20, 2013 9:52:58 AM UTC-5, WB wrote:

In article , Tony wrote: If you're using a pulley why not just have a release on the tow vehicle? Hi Tony, I was unclear about the pulley launch. The pulley is on the tow vehicle. One end of the line is anchored, the line goes over the pulley to the glider. The tow vehicle is pulling from the middle of the rope, going in the same direction as the glider. The advantages are that acceleration at the glider is almost as fast as a winch launch and the tow car only has to go 25-30 mph maximum to launch the glider. No gear changes required, and the low vehicle speed means it can be done on less than paved surfaces. Launching with 4000 feet of dacron rope and an old LTD with 500 lbs of bricks in the trunk used to get our Ka-8 to 2000' if we had a bit of headwind. A release can be put at the anchor point, but that's a long way from where the action is. There are some other disadvantages to this type of ground launch as well. Turn around time is fairly long. Switching ends of the rope after each launch can speed things up especially if the anchor point is another vehicle. Rope recovery can be problematic since a chute is usually not part of the rope end hardware, so the rope tends to fall a ways downwind.



ah i see, i was thinking of a fixed pulley.

Yes, fixed pulley has some advantages: quick turnaround, can use a chute, driver
is facing the action. The disadvantage is that you drag the whole rope the
length of the field at speed. I would think that would wear out Spectra
pretty fast. There's some places that use multiple pulleys that can
mitigate some of that. Check out the pulleylaunch Yahoo group for that.

Matt

On Monday, May 20, 2013 10:02:54 AM UTC-6, wrote:
On Monday, May 20, 2013 11:00:54 AM UTC-4, Tony wrote:

On Monday, May 20, 2013 9:52:58 AM UTC-5, WB wrote:



In article , Tony wrote: If you're using a pulley why not just have a release on the tow vehicle? Hi Tony, I was unclear about the pulley launch. The pulley is on the tow vehicle. One end of the line is anchored, the line goes over the pulley to the glider. The tow vehicle is pulling from the middle of the rope, going in the same direction as the glider. The advantages are that acceleration at the glider is almost as fast as a winch launch and the tow car only has to go 25-30 mph maximum to launch the glider. No gear changes required, and the low vehicle speed means it can be done on less than paved surfaces. Launching with 4000 feet of dacron rope and an old LTD with 500 lbs of bricks in the trunk used to get our Ka-8 to 2000' if we had a bit of headwind. A release can be put at the anchor point, but that's a long way from where the action is. There are some other disadvantages to this type of ground launch as well. Turn around time is fairly long.. Switching ends of the rope after each launch can speed things up especially if the anchor point is another vehicle. Rope recovery can be problematic since a chute is usually not part of the rope end hardware, so the rope tends to fall a ways downwind.







ah i see, i was thinking of a fixed pulley.



Yes, fixed pulley has some advantages: quick turnaround, can use a chute, driver

is facing the action. The disadvantage is that you drag the whole rope the

length of the field at speed. I would think that would wear out Spectra

pretty fast. There's some places that use multiple pulleys that can

mitigate some of that. Check out the pulleylaunch Yahoo group for that.



Matt

Yes, dragging a rope will wear it out. The car doing the dragging will also wear out fairly quickly. Auto tow is like drag racing - it puts a lot of strain on a car.

Of course, start-up costs for auto tow are lower than a winch which makes it attractive but in the medium term (Say two years) a winch is much cheaper to operate. There are about 1500 clubs worldwide which use ground launch but only a handful use auto tow. They've found a winch is quicker, cheaper, safer and gets the glider higher using less space.

By the time you've replaced a few ropes and tow cars, a winch starts looking pretty cheap.

In article ,
Bill D wrote:

Matt

Yes, dragging a rope will wear it out. The car doing the dragging will also
wear out fairly quickly. Auto tow is like drag racing - it puts a lot of
strain on a car.

Of course, start-up costs for auto tow are lower than a winch which makes it
attractive but in the medium term (Say two years) a winch is much cheaper to
operate. There are about 1500 clubs worldwide which use ground launch but
only a handful use auto tow. They've found a winch is quicker, cheaper,
safer and gets the glider higher using less space.

By the time you've replaced a few ropes and tow cars, a winch starts looking
pretty cheap.

Yep, we did that. We did the pulley ground launch until the club's
founder, Glen Lawler, built the "Eagle Winch". We happily used it for
several years before a change if airfield made winch use untenable
(crossing runway, not enough runway length). Last I heard, the winch was
at Philly Gliding Council. I miss it. We once launched half a contest
grid with it. The other poor, benighted sods without a ground launch
endorsement had to suffer aerotow.


Speaking of Glen's winch, it had a wide drum requiring an active level
wind mechanism to lay the line on evenly. Glen's level wind was a neat
bit of engineering involving a slotted bar that cammed the guide back
and forth across the drum. Have seen some pretty expensive winches that
had level winds mechanisms that did the job, but were clearly not as
precise as Glen's. Given that, if designing a winch, I'd go for simple
with a large diameter drum that would not need an active level wind.

It is possible and highly desirable to fit a guillotine to a pulley system. My club had considerable experience with reverse pulley for many years when we had a hard runway, and developed it to a great degree.

Method: We had 2 pulley wheels in a frame which pivoted about a horizontal axis, and also mounted so that it could swing sideways. This enabled the cable to run true from glider to one pulley, and from the other pulley to the tow vehicle. Both pulleys were framed in lead-in guards. The horizontal pivot was hollow. A spring loaded chisel-edged cutter ran through it. This could be released from the cab of the truck on which the pulley system was mounted. It would hit the cable, against an anvil mounted between the two pulleys. It worked.

Reason: Cable hang-ups at the glider end are not unknown. One fatal accident in the UK in the 1970’s arose from this (either release hook did not work, or cable wrapped round wheel, on a winch launch). With the cable taut, the glider described an arc from nearly above the winch to the ground. A non-fatal accident from a similar cause was addressed by the pilot circling over the winch while descending, straightening up with slack in the cable near the ground and landing downwind.

Mitigation: Plastic hose round the strop from weak link/drogue to glider prevents hang-up round the wheel/axle, but faulty cable release in the glider still needs the safety of a guillotine.

Chris N

In article ,
Chris Nicholas wrote:

It is possible and highly desirable to fit a guillotine to a pulley system.
My club had considerable experience with reverse pulley for many years when
we had a hard runway, and developed it to a great degree.

Method: We had 2 pulley wheels in a frame which pivoted about a horizontal
axis, and also mounted so that it could swing sideways. This enabled the
cable to run true from glider to one pulley, and from the other pulley to the
tow vehicle. Both pulleys were framed in lead-in guards. The horizontal pivot
was hollow. A spring loaded chisel-edged cutter ran through it. This could be
released from the cab of the truck on which the pulley system was mounted. It
would hit the cable, against an anvil mounted between the two pulleys. It
worked.


Sounds like an excellent setup. If we ever do groundlaunch again, we
will have to put together a guillotine system like that. Your guillotine
sounds almost identical to the one Glen Lawler put on the Eagle Winch.
It was a spring loaded chisel firing against an anvil. A hydraulic jack
was used to cock the thing. Made a heck of bang when fired. It would
shear steel rope like it was made of air. Not sure how well it worked on
Spectra, but I would expect that it had no trouble with it, especially
with any tension on the line.

Matt

Yes, dragging a rope will wear it out. The car doing the dragging will also
wear out fairly quickly. Auto tow is like drag racing - it puts a lot of
strain on a car.

Of course, start-up costs for auto tow are lower than a winch which makes it
attractive but in the medium term (Say two years) a winch is much cheaper to
operate. There are about 1500 clubs worldwide which use ground launch but
only a handful use auto tow. They've found a winch is quicker, cheaper,
safer and gets the glider higher using less space.

By the time you've replaced a few ropes and tow cars, a winch starts looking
pretty cheap.


We shortened the life of a Nissan Pathfinder transmission autolaunching
at remote locations. Our primary launch car at home was straight out of
a scrap yard. It was an old LTD with a big motor, maybe a 460. I think
it actually only ran on 5 cylinders though. The transmission was crap
but it worked in low gear and reverse. That was all we needed. Oh, and
the 500 lbs of salvaged brick wall that we put into the trunk to hold
the back end down when the glider was at the top of the climb.