"Bob Johnson" wrote in message
...
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

I can attest to Bob Johnson's statement that the Permian Soaring Association
winch is a very energetic machine. I took a launch in their L-13 last
November with Bob driving the winch and Craig Freeman coaching me from the
back seat. Bob's spreadsheets and that neck snapping launch go a long way
to convince me that the ubiquitous Chevy 454 is a very good winch engine.
In their case, the 454 is a very appropriate engine.

I still am holding out for a diesel though. Some of the older diesels were
slow to spool up but the newer electronically-controlled, turbocharged,
common-rail diesels are just as snappy as spark ignition engines according
to the operators I have spoken with. The low cost of operation, low
maintenance and massive low-end torque of diesels are real plusses.

If you plan to build a winch for any glider that might show up for a launch,
you have to consider gliders like a ASH 25 at 2200 pounds gross. My single
seat Nimbus could be over 1400 pounds with water ballast. If you add to
that the summer 15,000 foot + density altitudes of many of the very
attractive winch runways in the western USA, the power requirements go way
up.

Someone correctly pointed out that turbocharged diesels will maintain their
power to very high altitudes. However, even with sea level power, at zero
wind and high density altitude, the glider will have to be accelerated to a
far higher groundspeed to reach liftoff airspeed. It's that high cable
speed just after liftoff times the 1G cable tension that adds up to the big
HP demand.

From a practical and perhaps simplistic view, excess horsepower is no
problem since you don't have to use all that is available. Insufficient HP
is a problem you just can't get around.

Bill Daniels