Winch Physics

This has been covered in these pages before, but it may be timely to
post it again in view of the coming fuel price squeeze and the increased
interest in winching.

This Excel spreadsheet explains mathematically why a winch system
comprised of lighter linear (rope) and rotational elements will
significantly out-accelerate a more-massively built winch. Read petrol
powered vs. Diesel powered.

The Diesel, despite its other admitted advantages (or perhaps because of
them) will take longer to "wind up". The diesel engine is more massive
than a petrol engine in the crankshaft and flywheel, and in all other
moving parts. I do not know the exact masses of the two types of prime
movers. Perhaps someone out there can contribute this information. The
dry weights of the two power plants might be sufficient information.

This longer "wind up" period results in fewer "G's" being applied to the
sailplane being launched during the acceleration from rest to flying
speed and the subsequent start of the pull-up and climb.

We find with our 454 c.i. petrol engine-powered and Plasma rope-equipped
winch that our Blanik L-13 with two souls on board (1100 lb-mass) will
be flying before we can get the throttle fully advanced. We can easily
break a 1000-lb weak link during acceleration, but can't do so with a
1360-lb "blue" link.

Quicker than this I do not know how you could go.

The numbers add up to close to 1 "G" for the heavy two-place. Since
these maths are on a spreadsheet, all items comprising the entire system
can be changed to fit your particular situation. And all units have been
worked out on both the "English" and metric systems.

My spreadsheet had nothing to do with Craig Freeman's excellent winch
design for the Permian Soaring Asscociation. Rather, I did the
spreadsheet to find out just why it was so excellent.

http://www.permiansoaring.us/ (See "Special Projects")

The Excel spreadsheet is available as an email attachment. Let me know
if you would like me to send you one.

Cheers,

Bob Johnson Midland, Texas