On Wednesday, January 2, 2019 at 12:59:47 AM UTC-7, John Foster wrote:
On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote:
On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote:

There is nothing new under the sun when it comes to ground launching,
auto tow, winch, whatever. It's pretty much all been tried. Derek Piggot
wrote a book that is a great resource for learning about ground launch
in it's many forms. Unfortunately, it appears to be out of print.

ITYM "Gliding - A handbook on Soaring Flight"

Edition 7, which I have (blue cover showing a DG-800B with its motor
out), has two chapters on ground launching and is currently on offer from
Amazon for $3.60. His books may be out of print, but you can easily find
copies. Amazon even has a Derek Piggott author page.


--
Martin | martin at
Gregorie | gregorie dot org

That books looks promising. Thanks for the link.

With regard to the pulley: what diameter would it need to be? I've seen somewhere that a higher grade of UHMWPE--New England STS-12 (formerly Endura 12), recommends a sheave:rope diameter ratio of 8:1. That would mean for a 1/8" rope, one could get away with a sheave of only 1" in a pulley. Somehow that just doesn't seem like a good idea in this application though, but I don't know. So I'm asking.

If this were the case then, one could simply order these items off Amazon and be done with it:
https://www.amazon.com/Smittybilt-27...s=snatch+block
https://www.amazon.com/dp/B01I25Z5F4...v_ov_lig_dp_it

8 inches is okay, but there are other reverse pulley considerations. If you want the wheel to track the glider climb and drift, as in the old Cotswold system, a larger diameter is probably better. It was an effective 50" radius using using small rollers to reduce any stored energy in the system, which was an issue with the Essex GC system. With UHMWPE rope, you want to eliminate both stored energy and the ability for slack rope to tuck into any gaps or result in loops that might impact on the ground or equipment. Larger rope types might help with some of this, but there are always compromises of performance and price. UV resistence, abrasive resistence, fatigue (as a result of loading cycles), and ease of handling (including splicing) are all considerations.

This might be a suitable substitute for UHMWPE ropes for reverse pulley, http://www.novabraid.com/rope/oletec-12/ though they make no claims on abrasion resistance. 3/8" might be so heavy as to cause abrasive issues. This was true on the Cotswold system using solid wire. 10 gauge was heavy enough to cause excessive wear on the "memory loops" on the wire, so 13 gauge was found to give the best performance. Use of solid wire is not recommended at public use airports wherever you are because a large clear zone is needed in case of wire breaks. Many of these new ropes have negligible stretch, thus no recoil issues. Solid wire and steel wire ropes have significant recoil hazards.

Frank Whiteley