Winching - Reverse Auto Tow

On Tuesday, July 19, 2016 at 10:25:55 AM UTC-6, Steve Leonard wrote:
On Tuesday, July 19, 2016 at 10:22:07 AM UTC-5, wrote:

I'm not sure I see much advantage of a 2:1 system (assuming you mean the reverse-driving vehicle has a pulley as well). Wouldn't you still be dragging 4,000 ft of rope behind the tow vehicle (from the fixed pulley)? It hardly seems worth the extra rigging trouble...but I've never done it either.. My primary concern is rope wear, and I'm not seeing much improvement with that. Please let me know what I am missing.

Stephen

End of rope is anchored to the ground. Rope goes around pulley on the launch car, then back to the glider. Car travels half the speed of the glider (2:1 system). The only rope moving relative to the ground during the launch is the rope between the pulley and the glider. And similar to a winch launch, all that rope becomes airborne pretty quickly.

Steve Leonard

Thanks Steve. I was thinking about the rope being fixed at the end of the runway opposite the glider, going around a pulley on the tow vehicle, then back to a pulley next to the fixed end (again...opposite the glider). I was thinking that the only advantage was mechanical (1/2 speed). Now it's clear to me.

During the 1960's and early 1970's the Dansville (NY) Soaring Club primarily used the car-pulley system as described above by Steve. The anchor was in the grass adjacent to the runway and midfield. The cars drove on the runway to avoid tearing up the grass. The system worked very well at a cost of $1 per tow and tow rope wear was reasonable, although rope breaks were quite common. Having a Chrysler dealer as a club member who provided old and large V8 junk cars, with excellent cooling systems, was essential to the fiscal viability of the car-pully operation. About 9" high runway lights were installed in the early 1970's which required addition of thin tube tripods that covered each light to allow the rope to slip over the light rather than tearing up the light. Later the runway lights were replaced with ones that are about 2ft high which made car-pulley launches not viable.

On Tuesday, July 19, 2016 at 10:25:55 AM UTC-6, Steve Leonard wrote:
On Tuesday, July 19, 2016 at 10:22:07 AM UTC-5, wrote:

I'm not sure I see much advantage of a 2:1 system (assuming you mean the reverse-driving vehicle has a pulley as well). Wouldn't you still be dragging 4,000 ft of rope behind the tow vehicle (from the fixed pulley)? It hardly seems worth the extra rigging trouble...but I've never done it either.. My primary concern is rope wear, and I'm not seeing much improvement with that. Please let me know what I am missing.

Stephen

End of rope is anchored to the ground. Rope goes around pulley on the launch car, then back to the glider. Car travels half the speed of the glider (2:1 system). The only rope moving relative to the ground during the launch is the rope between the pulley and the glider. And similar to a winch launch, all that rope becomes airborne pretty quickly.

Steve Leonard

That will probably give the most rope life for UHMWPE or dacron ropes.

http://linearcomposites.net/media/pa...e_study_13.pdf
Used 500m lengths of this for autotow and got 1500ft launches with L-13 and G-103. Doesn't like pulleys I'm told. Another poster said they had frequent breaks. Wasn't my experience. Rather heavy.

Frank Whiteley

End of rope is anchored to the ground. Rope goes around pulley on the
launch car, then back to the glider. Car travels half the speed of the
glide r (2:1 system). The only rope moving relative to the ground during
the launch is the rope between the pulley and the glider. And similar to a
winch =
launch, all that rope becomes airborne pretty quickly.

There may be a snag to that....

The amount of rope between the glider and the car is shortening all the
time, and the pilot is alive at the start of the tow ?

On Thursday, July 21, 2016 at 8:15:08 PM UTC+12, Peter Higgs wrote:
End of rope is anchored to the ground. Rope goes around pulley on the
launch car, then back to the glider. Car travels half the speed of the
glide r (2:1 system). The only rope moving relative to the ground during
the launch is the rope between the pulley and the glider. And similar to a
winch =
launch, all that rope becomes airborne pretty quickly.

There may be a snag to that....

The amount of rope between the glider and the car is shortening all the
time, and the pilot is alive at the start of the tow ?

Exactly the same as with a winch, you mean?

Except in this case the winch is moving.

On Thu, 21 Jul 2016 08:06:34 +0000, Peter Higgs wrote:

End of rope is anchored to the ground. Rope goes around pulley on the
launch car, then back to the glider. Car travels half the speed of the
glide r (2:1 system). The only rope moving relative to the ground during
the launch is the rope between the pulley and the glider. And similar to
a winch =
launch, all that rope becomes airborne pretty quickly.

There may be a snag to that....

The amount of rope between the glider and the car is shortening all the
time, and the pilot is alive at the start of the tow ?

That looks similar to the winch situation to me: in both cases the
effective rope gets shorter during the launch.

- with a winch you get roughly 1/3 the height of the rope length
in calm conditions, so 2/3 of the cable has been wound in at
release, and a lot more if there's wind to help the glider kite
while the winch slows down.

- on a 2:1 factor auto tow the height:rope length ratio must depend
on where the anchor peg is along the runway. If its at the launch
point the height gain will be poor, but if its half-way down the
run, the worst case would be launching to 1/2 the height of the
rope length and, like the winch, a lot higher with wind to help.

The main disadvantages compared with a two drum winch is that the launch
rate will be lower (cable must be retrieved after every launch vs after
every two launches) and each retrieve will be slower because the tow car
needs to:

- detach from the cable
- find the end
- tow that back to the launch point
- go back up the field and put the cable back on his pulley

compared with:

- drive the cable truck to the winch (or follow the first launch down)
- hook both cables on
- drive back to the launch point

Did I miss anything?


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

There may be a snag to that....

The amount of rope between the glider and the car is shortening all the
time, and the pilot is alive at the start of the tow ?

That looks similar to the winch situation to me: in both cases the
effective rope gets shorter during the launch.

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.

There may be a snag to that....

The amount of rope between the glider and the car is shortening all the
time, and the pilot is alive at the start of the tow ?

That looks similar to the winch situation to me: in both cases the
effective rope gets shorter during the launch.

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.

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???

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. However, this is all theoretical because
I've never done an auto-tow or seen it done: most of my flying is done
from a winch.

So, here are some questions for those who have used the 2:1 auto-tow
system. I'd enjoy seeing the answers as they'd help me get my head around
how the system works in practise:

- where is the stationary end of the rope anchored along the runway?
- what ratio of launch height:rope length is usual on a calm day?
- on a windy day?
- does the glider ever tend to lift the rear of the tow vehicle,
allowing wheel spin, etc?


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