On Friday, December 28, 2018 at 8:33:58 PM UTC-7, John Foster wrote:
On Sunday, April 29, 2018 at 4:22:59 PM UTC-6, Frank Whiteley wrote:
On Sunday, April 29, 2018 at 3:30:06 AM UTC-6, Paul T wrote:
At 20:43 28 April 2018, Chris Rowland wrote:
I did most of my ab initio training and learning to be an instructor
o
autotow.
I'd suggest avoiding reverse pulley because it's difficult for both
the to
car driver and pilot to know when to finish the launch. With
straigh
autotow it's easy, stop sufficiently before the end of the runway
that yo
can drive forward and lay the cable out.
Another issue is cross winds. The cable will drift downwind and
looking a
Ronan on Google Earth there are fields with irrigation equipment
there. Th
farmers will take a dim view of the launch cable being dragged
throug
their irrigation kit.
Chris
Don't see what the problem is at all with reverse pulley - had many
launches that way - the other end of the runway is just as easily
visible to the tow car driver and as speed decays the glider pilot
pulls off - think you creating an issue where none exists.
If you have a straight reverse pulley system and set it up properly,
with removable strops t both ends the cable is waiting for the next
glider, the car drives back and connects to the other end of the cable
and your ready to launch again.
Some reverse pulley systems where just way over the top -KISS is
the answer. Doubt these guys will be doing hundreds of launches a
day.
Crosswinds are something every ground launching site has to
contend with and 1000's of sites around the world seem to manage
ok with proper training - seem to remember the advice was to have
at least 80m width of clear land to launch from.
http://coloradosoaring.org/thinking_...ey/default.htm
I've had a couple of chats with John Foster. There are raised runway lights. Reverse pulley allows a lot more control of the line than direct auto tow, so could be an option. Today, UHMWPE ropes, spectra, dyneema, or polyolefin drag line might work for reverse pulley, though I'm unaware of an operation doing so.
Frank Whiteley
Sorry to dig up this old thread, but now that winter has set in, I'm starting to think and plan more on this project. Do you happen to know where one could get one of these "polyolefin drag lines"? I've looked around a bit, but haven't seen any links for such. I'm also considering various designs for the pulley system. The one that you have linked from the Cotswold GC in Great Britain looks like it would take some effort to build. I've wondered about conscripting an old motorcycle wheel for this purpose and welding up a frame with guides for it to attach to a tow hitch of a pick-up truck. Any proven designs out there like this?
The Essex GC one had a reverse pulley set up. However the rig had a lot of stored energy in the pulley wheels. So a wire break could involve quite a mess. I launched on this rig a few times. I think the Cotswold rig was better. In both iterations, solid wire needs considerably more safety area than other methods.
The Cotswold GC was 200 members and 70 gliders. They also owned tow planes, mostly for wave days.
Now, they did pack in the reverse-pulley for a winch. Not sure exactly why, but cost was not the first consideration.
Frank Whiteley