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.