Winching - Reverse Auto Tow

On Thursday, July 21, 2016 at 3:18:23 PM UTC+3, Martin Gregorie wrote:
On Thu, 21 Jul 2016 10:30:00 +0000, Peter Higgs wrote:

That is quite true, except with the winch you have the full runway
length of rope between winch and glider.

With the Car, you can only start with half that distance from car to
glider.

That assumes the end of the rope is anchored at the launch point, which
looks like a worst case scenario. If the anchor is somewhere along the
runway, in theory at least, you can do a lot better. Putting the anchor
at the midpoint with the car starting at the 3/4 mark should launch to a
height of half the rope length.

That doesn't make sense. The anchor point can be anywhere at all at or behind where the car starts from, including next to the glider, or behind it. It's only dead (unused, wasted) rope length from the car to the anchor point..

If you want to be able to reel in (nearly) the entire length of rope after glider release, as is commonly done with a winch, then you're limited to the car starting at most half way along the runway so that the rope is fully retrieved as the car nears the far end of the runway.

It's hard to figure out what release height you might get.

Assuming a standard winch launch gets 33.33% of the runway length in height, and assuming the glider averages the same climb angle with a 2:1 auto launch with the car starting from the runway mid point, then release will occur with the car about 75% of the way down the runway, and the glider at a height 25% of the runway length.

On Thu, 21 Jul 2016 06:18:46 -0700, Bruce Hoult wrote:

On Thursday, July 21, 2016 at 3:18:23 PM UTC+3, Martin Gregorie wrote:
That assumes the end of the rope is anchored at the launch point, which
looks like a worst case scenario. If the anchor is somewhere along the
runway, in theory at least, you can do a lot better. Putting the anchor
at the midpoint with the car starting at the 3/4 mark should launch to
a height of half the rope length.

That doesn't make sense. The anchor point can be anywhere at all at or
behind where the car starts from, including next to the glider, or
behind it. It's only dead (unused, wasted) rope length from the car to
the anchor point.

Draw a diagram: I had to before I could work out what was what.

Lets assume a 4000 ft run and 4000 ft of rope.

With the rope anchored at the launch point, the car will start at the
midway mark because that is when the slack will be out of the rope. Its
equally sure that when the car has driven 1000 ft from there, the glider
will be 1000 ft from the car and so cannot be higher than 25% if the rope
length.

With the rope anchored at the 2000 ft mark, the car has to be 3000 ft
from the launch point for all 4000 ft of rope to be tight. If the car
then drives the 1000 ft to the end of the run, the glider still has 2000
ft of rope between it and the car, so in theory could be at 2000 ft.

As you say, calculating what happens with other anchor points is hard.

Never having seen one of these launches I don't know if that happens or
how far back and lower the glider would be in reality, but I bet the F3J
radio glider boys know all about optimising a single moving pulley launch
because some of them do it all the time, typically with the line anchored
at the launch point (an F3J requirement IIRC) and with two fit guys
pulling on the pulley to fire the model off as high as they can get it.

Assuming a standard winch launch gets 33.33% of the runway length in
height, and assuming the glider averages the same climb angle with a 2:1
auto launch with the car starting from the runway mid point, then
release will occur with the car about 75% of the way down the runway,
and the glider at a height 25% of the runway length.

Exactly so - and if you move the anchor point halfway down the run, the
car will be at the 3/4 point when the slack is out and 3/4 of the line is
still between the car and glider, but what I don't know is how far up the
glider will be when the car gets to the end of the run.

There has to be an optimum anchor point, but, guessing wildly, I suspect
its less than half-way down the run from the glider.


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

On Thursday, July 21, 2016 at 5:31:35 AM UTC-6, Dave Nadler wrote:
On Thursday, July 21, 2016 at 6:30:04 AM UTC-4, Peter Higgs wrote:
That is quite true, except with the winch you have the full runway length
of rope between winch and glider.
With the Car, you can only start with half that distance from car to
glider.

If OP is at Hobbs, there's no lack of space.
With a payout winch, its possible to drive around the corners
of the huge triangular airfield and keep climbing.
Don't know if anybody that does so with a glider, but I did that
with a hang-glider back when Curt Graham had a hang-glider
operation at Hobbs (kinda weird flying around the corner
on a ground launch).

Payout winch keeps line almost always off the ground,
uses more of available space - anybody doing glider (sailplane)
payout launches these days???

Gary Boggs has extensive experience with this. If his rig is still running strong, a visit to Hobbs may be in order.

On Thursday, July 21, 2016 at 7:03:33 PM UTC+3, Martin Gregorie wrote:
On Thu, 21 Jul 2016 06:18:46 -0700, Bruce Hoult wrote:

On Thursday, July 21, 2016 at 3:18:23 PM UTC+3, Martin Gregorie wrote:
That assumes the end of the rope is anchored at the launch point, which
looks like a worst case scenario. If the anchor is somewhere along the
runway, in theory at least, you can do a lot better. Putting the anchor
at the midpoint with the car starting at the 3/4 mark should launch to
a height of half the rope length.

That doesn't make sense. The anchor point can be anywhere at all at or
behind where the car starts from, including next to the glider, or
behind it. It's only dead (unused, wasted) rope length from the car to
the anchor point.

Draw a diagram: I had to before I could work out what was what.

Lets assume a 4000 ft run and 4000 ft of rope.

With the rope anchored at the launch point, the car will start at the
midway mark because that is when the slack will be out of the rope. Its
equally sure that when the car has driven 1000 ft from there, the glider
will be 1000 ft from the car and so cannot be higher than 25% if the rope
length.

Now consider a 4000 ft run and 2000 ft of rope, with the rope anchored halfway down the runway and the car also starting from the midway point. The analysis is absolutely identical, but you've saved the expense of 2000 ft of rope.

Draw a diagram.


With the rope anchored at the 2000 ft mark, the car has to be 3000 ft
from the launch point for all 4000 ft of rope to be tight. If the car
then drives the 1000 ft to the end of the run, the glider still has 2000
ft of rope between it and the car, so in theory could be at 2000 ft.

The car stops (there's no space in front of it), the glider releases, and you now have 2000 ft of rope flopping to the ground uncontrolled. Doesn't sound like a good idea to me.

Once again: The anchor point can be anywhere at all at or behind where the car starts from, including next to the glider, or behind it. It's only dead (unused, wasted) rope length from the car to the anchor point.

What counts is the length of rope from the glider to the car at the start, and the distance the car has available to drive from there.

The length of rope from the car starting point back to the anchor is absolutely irrelevant to anything .. it just lays there and does not affect the launch in any way.

Assuming a standard winch launch gets 33.33% of the runway length in
height, and assuming the glider averages the same climb angle with a 2:1
auto launch with the car starting from the runway mid point, then
release will occur with the car about 75% of the way down the runway,
and the glider at a height 25% of the runway length.

Exactly so - and if you move the anchor point halfway down the run, the
car will be at the 3/4 point when the slack is out and 3/4 of the line is
still between the car and glider

My analysis didn't specify where the anchor point is. It could be next to the glider, it could be next to the car starting point. Makes no difference at all as long as there is exactly enough rope to go from the glider to the car to the anchor point.

There has to be an optimum anchor point, but, guessing wildly, I suspect
its less than half-way down the run from the glider.

The anchor point makes no difference, as long as it's at least vaguely behind the car starting point.

On Sunday, November 2, 2003 at 1:49:20 PM UTC-5, wrote:
Can anyone direct me to Clubs / Web sites using this method of launching -
Interested in finding out more about this method, particularly from clubs
that operate from gravel/dirt strips

Thank you


John Spargo

Bruce: I can give you some quantitative numbers. In 1966-67 I made ~70 car-pulley tows in a 1:26 at Dansville using an asphalt runway that is almost 4000ft in length. The average tow was to 1300ft with some tows to 1500ft when the wind was optimum. For comparison, in 2009 I gave many instruction winch flights in either a Blanik L13 or a ASK21 using the same runway at Dansville. The average tow again was 1300ft and 1500ft when the wind was favourable. Thus under similar circumstances car pulley and winch give essentially the same height. Winch tows can utilize the full length of the airfield whereas car pulley tows are limited to the length of the paved surface because of the damage caused driving on the grass. Also winch tows are less intrusive than car pulley if the airport has mixed power and glider activity.

Doug C

On Thursday, July 21, 2016 at 5:31:35 AM UTC-6, Dave Nadler wrote:
On Thursday, July 21, 2016 at 6:30:04 AM UTC-4, Peter Higgs wrote:
That is quite true, except with the winch you have the full runway length
of rope between winch and glider.
With the Car, you can only start with half that distance from car to
glider.

If OP is at Hobbs, there's no lack of space.
With a payout winch, its possible to drive around the corners
of the huge triangular airfield and keep climbing.
Don't know if anybody that does so with a glider, but I did that
with a hang-glider back when Curt Graham had a hang-glider
operation at Hobbs (kinda weird flying around the corner
on a ground launch).

Payout winch keeps line almost always off the ground,
uses more of available space - anybody doing glider (sailplane)
payout launches these days???

Gary Boggs, NW Sky Sports, is the only one I'm aware doing this in recent years. He's now in Peoria, AZ. Not sure his rig made the trip from Oregon.

I did a lot of auto tow launching with the Bath & Wilts club at Keevil in the late 60s and 70s. We used F100s initially, then a variety of trucks and lorries.
We started with piano wire but moved to Parafil after the RAF resurfaced the main runway with a very abrasive surface that wore out piano wire very rapidly - in 8 launches on one occasion.

We tried reverse pulley but it wasn't successful. Our inexperience meant that it was difficult to know when the glider was at the top of the launch and stop and if the pilot hung on the cable would break. From what I've read here we were probably trying too hard and should have backed off a lot earlier.

With auto tow on one runway we would turn to go along the peri track to extend the run. This was fun because the glider was now pulling at an angle and the heavier two seaters would lift the back of the truck and move it sideways - it was a bit like driving a wheelbarrow.

Chris Rowland

Does anyone have particularly bad experiences with pulleys used like this. I am talking about the pulleys themselves. Has someone found a particular diameter that is too small. Obviously larger is better for both bearing speed and rope bending, but there are limitations on cost and availability....particular for the trial run I'm thinking about. I am considering a trial run with a swiveling pulley on the receiver hitch of a pickup, no guides, just the pulley, with around 8,000' of 1/4" poly hollow braid, flying a 1-26. That should prove the launch height, assuming the rope doesn't break on the first launch. I'm not sure what to expect at the pulley end, and don't want the rope jumping out of the sheave, catching and breaking. I doubt it will, but have no experience to back it up.

On Tuesday, 26 July 2016 02:12:58 UTC+1, wrote:
Does anyone have particularly bad experiences with pulleys used like this.. I am talking about the pulleys themselves. Has someone found a particular diameter that is too small. Obviously larger is better for both bearing speed and rope bending, but there are limitations on cost and availability....particular for the trial run I'm thinking about. I am considering a trial run with a swiveling pulley on the receiver hitch of a pickup, no guides, just the pulley, with around 8,000' of 1/4" poly hollow braid, flying a 1-26. That should prove the launch height, assuming the rope doesn't break on the first launch. I'm not sure what to expect at the pulley end, and don't want the rope jumping out of the sheave, catching and breaking. I doubt it will, but have no experience to back it up.

Hi, I wrote an article "The Expedition Pilot's guide to launching" in the Dec2013/Jan 2014 edition of the UK Sailplane and Gliding magazine. It may be of interest. I use 12mm diameter high density polypropylene rope (Skyrope from Skylaunch) on snatch blocks with, initally steel pulleys on plain bearings 110mm dia. The bearings cooked in spite of lots of grease! These have been modified for regular use to nylon pulleys with steel ball bearings. The steel flaps or cheeks of the snatch blocks keep the rope where it should be. I use either a 2 to 1 or 3 to one system to keep the tow speed down ( we use some rough fields). If you are serious then I can send you a copy of the article and details of the kit, as well as the links to YouTube videos of some launches in the Lake District (UK) using 2 to 1 pulley system, with one pulley on a ground anchor and the other on the car's tow hitch (with the rope tail to another ground anchor). Everything used is inexpensive, and it works. Pete Whitehead

I would get a 15 to 17 inch rim from a junk yard. Cheap, steel, plain. Then, get a stub axle and hub from Tractor Supply or the like with at least a 2000 lb load rating. No need for guides. No need for swivels. Axis of rotation for the wheel to be horizontal, running side to side. Your pull off angles to the side (for the anchor, or the glider while climbing) will never be more than a few degrees, and the rope will not want to climb out of the deepest part of the wheel. Don't add more complication than is needed. With 8000 feet of ramp, you probably don't need much more than 6000 feet of rope.

If you are anchoring the pulley (say, to a parked car), still no need for a swivel. Keep your life simple!

Just my two cents worth.

Steve Leonard