On Tuesday, May 21, 2013 8:10:22 AM UTC-6, WB wrote:
In article ,

Chris Nicholas wrote:



It is possible and highly desirable to fit a guillotine to a pulley system.

My club had considerable experience with reverse pulley for many years when

we had a hard runway, and developed it to a great degree.



Method: We had 2 pulley wheels in a frame which pivoted about a horizontal

axis, and also mounted so that it could swing sideways. This enabled the

cable to run true from glider to one pulley, and from the other pulley to the

tow vehicle. Both pulleys were framed in lead-in guards. The horizontal pivot

was hollow. A spring loaded chisel-edged cutter ran through it. This could be

released from the cab of the truck on which the pulley system was mounted. It

would hit the cable, against an anvil mounted between the two pulleys. It

worked.





Sounds like an excellent setup. If we ever do groundlaunch again, we

will have to put together a guillotine system like that. Your guillotine

sounds almost identical to the one Glen Lawler put on the Eagle Winch.

It was a spring loaded chisel firing against an anvil. A hydraulic jack

was used to cock the thing. Made a heck of bang when fired. It would

shear steel rope like it was made of air. Not sure how well it worked on

Spectra, but I would expect that it had no trouble with it, especially

with any tension on the line.

I suggest a cheaper and safer guillotine is a simple air cylinder powered by a portable air tank. I bought a new 2" bore Bimba cylinder on eBay for $15 and an air tank with pressure gauge from Harbor Freight for $25. A "pop-open" push-button air valve and some air hose completes the system.

A 2" cylinder produces exactly 3.1316 pounds-force for every PSI. The tank holds over 100 PSI so the cylinder can drive a chisel blade with at least 313 Lbs-F which WILL cut a rope. Checking the gauge on the tank assures you have air pressure. If necessary, refill with any shop air compressor. Unlike a steel spring, compressed air doesn't rust or lose strength with age..

Why is it safer? You can de-energize by just removing the air hose to the guillotine so there's no chance of losing a finger. Spring powered guillotines resemble bear traps and have to be relaxed VERY CAREFULLY to work on them.