Let's talk ground launching........

Hello Again:
Thank you all for the response, it is all very welcome. I do live in
South Texas and we have access to a basically un-used well kept
200'x6000' hard packed grass field. We have recently picked up an
older winch that needs a litte TCL but with a little work will be very
usable. We are also setting up for straight auto-tow and are in the
process of building pulleys for reverse pulley. One of the many
questions I have is this: is a parachute necessary on straight auto-tow
and if so how far from the glider should the parachute be located?
Many more questions later.
Thanks
Rusty

Chris Nicholas wrote:
16 gauge piano wire sounds remarkably thin, unless it was a special high
tensile type. Cotsold GC and Essex GC in the UK used 13 gauge (easier
than 11 gauge to handle, join, etc. but prone to breaks) or later 11
gauge (rarely broke, but harder to tie knots, and needed larger pulley
diameter for reverse pulley). The large diameters required led to
Cotswold going for a non-rotating "pulley" made up from lots of small
rollers round its rim (but it had no guillotine). Essex used two large
rollers, lots of inertia, but it enabled a flat anvil to be between them
so that a spring-loaded chisel could be released to cut the cable in
emergency.

Before reverse pulley, Essex used 13 gauge for straight autotow. It
often broke. Theoretically, the weak link should be weaker than the
cable, but we were using uncalibrated polypropylene rope of uncertain
breaking strain.

Starting over, I would be looking at Dyneema stronger than the highest
rated weak link needed, and the main cable should rarely if ever break.
For reverse pulley, I would look at the Cotswold type but incorporate a
flat part of the "pulley" with an anvil in line with the pivot, like the
Essex set up. The spring loaded chisel would go through the hollow pivot
shaft.

For the benefit of those who have not seen a pulley system, it needs to
pivot about a horizontal axle, and to swing to some extent, to equalise
the angles and allow the cable to run true from the glider (which might
be to one side of the runway, e.g. in a cross wind), into the top of the
pulley, and out from the bottom to the tow vehicle.

Chris N.




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Rusty wrote:
Hello Again:
Thank you all for the response, it is all very welcome. I do live in
South Texas and we have access to a basically un-used well kept
200'x6000' hard packed grass field. We have recently picked up an
older winch that needs a litte TCL but with a little work will be very
usable. We are also setting up for straight auto-tow and are in the
process of building pulleys for reverse pulley. One of the many
questions I have is this: is a parachute necessary on straight auto-tow
and if so how far from the glider should the parachute be located?
Many more questions later.
Thanks
Rusty

We did straight autotows for several years with a product known as
parafil. If there's a similar product, it might be a good option for
some. Some prior postings.

http://tinyurl.com/7em69

Frank

Chris Nicholas wrote:
16 gauge piano wire sounds remarkably thin, unless it was a special high
tensile type. Cotsold GC and Essex GC in the UK used 13 gauge (easier
than 11 gauge to handle, join, etc. but prone to breaks) or later 11
gauge (rarely broke, but harder to tie knots, and needed larger pulley
diameter for reverse pulley). The large diameters required led to
Cotswold going for a non-rotating "pulley" made up from lots of small
rollers round its rim (but it had no guillotine). Essex used two large
rollers, lots of inertia, but it enabled a flat anvil to be between them
so that a spring-loaded chisel could be released to cut the cable in
emergency.

Before reverse pulley, Essex used 13 gauge for straight autotow. It
often broke. Theoretically, the weak link should be weaker than the
cable, but we were using uncalibrated polypropylene rope of uncertain
breaking strain.

Starting over, I would be looking at Dyneema stronger than the highest
rated weak link needed, and the main cable should rarely if ever break.
For reverse pulley, I would look at the Cotswold type but incorporate a
flat part of the "pulley" with an anvil in line with the pivot, like the
Essex set up. The spring loaded chisel would go through the hollow pivot
shaft.

For the benefit of those who have not seen a pulley system, it needs to
pivot about a horizontal axle, and to swing to some extent, to equalise
the angles and allow the cable to run true from the glider (which might
be to one side of the runway, e.g. in a cross wind), into the top of the
pulley, and out from the bottom to the tow vehicle.

Chris N.

When using steel wire and wheels/pulleys, the diameter of the
wheels/pulleys should be 60 times the diameter of the wire to prevent
work hardening. That's why 7/7 wire rope works with much small
diameter rollers and guides on winches.

See http://tinyurl.com/c3pd5

Frank Whiteley

On Fri, 2 Sep 2005 10:15:14 UTC, Chris Nicholas
wrote:

: For reverse pulley, I would look at the Cotswold type but incorporate a
: flat part of the "pulley" with an anvil in line with the pivot, like the
: Essex set up. The spring loaded chisel would go through the hollow pivot
: shaft.

Who operates the guillotine in these systems? Do you need someone
stationed by the pulley, or is there some sort of remote actuation?

Personally, I think it's time we stopped messing about with spring
loaded cutters and went to explosive ones, but that's incidental here!

Ian

Ian Johnston wrote:
On Fri, 2 Sep 2005 10:15:14 UTC, Chris Nicholas
wrote:

: For reverse pulley, I would look at the Cotswold type but incorporate a
: flat part of the "pulley" with an anvil in line with the pivot, like the
: Essex set up. The spring loaded chisel would go through the hollow pivot
: shaft.

Who operates the guillotine in these systems? Do you need someone
stationed by the pulley, or is there some sort of remote actuation?

Personally, I think it's time we stopped messing about with spring
loaded cutters and went to explosive ones, but that's incidental here!

Ian
The Cotswold Reverse Pulley had no guillotine and the reasoning was
that none was needed. The design was such that the tow vehicle end
would release if there was a release failure and the glider would pull
wire and tackle back through the pulley, as needed. IIRC, there were
two release failures in the 30 years of operation and that both
recovered okay.

Frank Whiteley

Yes, you need a drogue, at least for piano wire cable. If not, it drops
into a terrible snarl-up. Dyneema/Spectra, I don't know - ask people who
have tried it.

For lengths and hardware on the cable, I have seen many different
variations. The most complex was at Dunstable, UK some years ago, which
included many features for which I could understand the reason,
including a long shock rope between drogue and rings. I believe that the
safest arrangement is short (2-6 feet), plastic-tube-covered strop from
Tost rings to Tost weak link; weak link with easy-change connections;
long strop (30-80 feet) from weak link to drogue (to keep billowing
drogue well in front of glider in a power failure situation); swivel;
and then main cable.

It is an official BGA "Recommended Practice" that the shock rope should
be stiffened with plastic hose or similar, to prevent it wrapping round
the wheel axle and being unable to release. There are, however, many
more aspects of the hardware that could usefully be standardised, or at
least listed for guidance so that if people do something different it
should be a conscious decision with good reason, not just ignorance or
lack of experience.

No doubt someone from Dunstable will correct the following if I got it
wrong or it has changed, but my notes of their assembly were as follows,
starting at the glider end:

1. Tost rings

2. wire rope a few feet long.

3. ferrule to secure end of 2 into a loop.

4. plastic hose over 2.

5. ferrule to secure other end of 2 into a loop.

6. oval link with flat section on one side.

7. quick-release hook mating with 6.

8. shackle.

9. weak link assembly.

10. shackle.

11. shock rope about 80 feet long.

12. shackle.

13. triangular ring on end of drogue.

14. drogue.

15. metal end fitting on drogue.

16. shackle.

17. plate on shackle to take the wear.

18. swivel.

19. shackle.

20. oval link with flat section on one side.

21. quick-release hook mating with 20.

22. loop of main winch cable.

23. first ferrule securing 22.

24. plate on loop to take the wear.

25. second ferrule securing 22 and 24.

Most of the hardware is standard off-the shelf stuff. The "plate . . .
to take the wear" looked like a special, and it was oval, about 2x3
inches and 1/4 inch thick (50x75 mm, 6 mm thick) and had two holes
through which the legs of the shackle projected. It had the effect of
being the largest diameter thing on the assembly, so would be the one to
take the wear from running over the ground, hence protecting swivel
etc..

I hope this helps.

Chris N.








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On Fri, 02 Sep 2005 13:35:49 +0000, Chris Nicholas wrote:

I'm not from Dunstable but.....

I think items 7 and 10 should be swapped so the weak link is part of the
wire strop assembly and item 4 should be selected so its colour matches
the colour of the weak link.

No doubt someone from Dunstable will correct the following if I got it
wrong or it has changed, but my notes of their assembly were as follows,
starting at the glider end:

1. Tost rings

2. wire rope a few feet long.

3. ferrule to secure end of 2 into a loop.

4. plastic hose over 2.

5. ferrule to secure other end of 2 into a loop.

6. oval link with flat section on one side.

7. quick-release hook mating with 6.

8. shackle.

9. weak link assembly.

10. shackle.

11. shock rope about 80 feet long.

12. shackle.

13. triangular ring on end of drogue.

14. drogue.

15. metal end fitting on drogue.

16. shackle.

17. plate on shackle to take the wear.

18. swivel.

19. shackle.

20. oval link with flat section on one side.

21. quick-release hook mating with 20.

22. loop of main winch cable.

23. first ferrule securing 22.

24. plate on loop to take the wear.

25. second ferrule securing 22 and 24.

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

Martin Gregorie wrote [snip] " . . .I think items 7 and 10 should be
swapped so the weak link is part of the wire strop assembly and item 4
should be selected so its colour matches the colour of the weak link."

Some clubs, including mine, do that - change the strop with weak link
attached, to suit the glider. Some have several weak links on the cable
and just switch the same strop from one to another. Some may just change
the weak link, with quick releases either side, so only one strop is
needed.

Chris N.






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On Fri, 02 Sep 2005 21:56:11 +0000, Chris Nicholas wrote:

Martin Gregorie wrote [snip] " . . .I think items 7 and 10 should be
swapped so the weak link is part of the wire strop assembly and item 4
should be selected so its colour matches the colour of the weak link."

Some clubs, including mine, do that - change the strop with weak link
attached, to suit the glider. Some have several weak links on the cable
and just switch the same strop from one to another. Some may just change
the weak link, with quick releases either side, so only one strop is
needed.

Chris N.

Apologies, Chris. I thought that you'd gotten confused with all the
shackles - the sort of thing I'd do.

The only club I've visited that swapped the weak link but not the strop
was Auckland, NZ - and they use a really long strop, at least 5 m, and
aero-tow rope in place of steel cable on the winch.

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

In message , Chris Nicholas
writes
Martin Gregorie wrote [snip] " . . .I think items 7 and 10 should be
swapped so the weak link is part of the wire strop assembly and item 4
should be selected so its colour matches the colour of the weak link."

Some clubs, including mine, do that - change the strop with weak link
attached, to suit the glider. Some have several weak links on the cable
and just switch the same strop from one to another. Some may just change
the weak link, with quick releases either side, so only one strop is
needed.

Fairly common practice that I have seen at all of the clubs I regularly
fly from (Cotswold, Mynd, Port Moak) go Tost Rings - shock rope - weak
link - quick change link.

The logic for this is that if you do break the weak link then you stand
a chance of finding the tost rings as they will have the shock rope that
is usually covered by a brightly coloured plastic pipe.

The shock rope length is about 6 to 10 feet long, port moak's is
shorter. Some clubs also choose coloured pipe to match the weak link
colour.

For What It's Worth. I fly from Cotswold and witnessed the last couple
of years of the reverse pulley system. It was simple to use but -

It was extremely tough on the vehicles with high maintenance costs and
effort;
The single strand wire broke very readily;
It was hard to get a good launch for heavier gliders;
The knots had to be cut out and re-made every morning before flying;
There was a significant dip in the launch just after rotation as the
truck gearbox changed gear.

We averaged 1,000 to 1,500 ft launches but did get to much higher on
occasion. (1 Mile Runway). We replaced the system with a Skylaunch
winch using stranded steel wire. This is much more repeatable and gets
launches between 1,400 and 1,800 feet with a much greater availability.

We fly gliders ranging from K8s to Duo Discus's and get good launches
with lots of good cross countries. We do have a tug on site which gets
used a fair amount but most people winch. One of our full cats managed
to get 30 mins with a T31 on Friday so it can't be that bad and he only
came down thinking that the owner (me) wanted it back.

Seriously, winching works well if you have a ridge within a straight
glide and if you have reasonable thermal sources around the airfield but
do get good instruction on it as it is easy to get into very bad habits
masked by the power of modern winches which will then bite you.

Hope this helps

Robin
Chris N.






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--
Robin Birch