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Safety of winch launch vrs. aero tow?



 
 
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  #51  
Old October 28th 03, 09:52 PM
Mike Borgelt
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On Tue, 28 Oct 2003 10:26:06 -0800, "Gary Boggs"
wrote:

I really appreciate all this good input, thank you all for responding. Now
for a new twist, one of our members has built a "pay out winch". A pay out
winch is a drum with a break on it. The glider hooks up about 200' behind
the tow vehicle, and as the glider climbs, the line spools out. Does
anybody have any experience with this type of launch? How much runway do
you need for this type of launch, how high can you get, ect?

Boggs


Don't know about that one but car tows generally aren't as good as a
winch as the initial accleration is much slower. You are accelerating
the car as well as the glider. The winch motor only accelerates the
glider and wire.

The car doesn't last very long in that sort of duty either.

Mike Borgelt
  #52  
Old October 28th 03, 10:11 PM
John Galloway
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Your on your own there I think.

John Galloway


At 18:36 28 October 2003, Gary Boggs wrote:
I really appreciate all this good input, thank you
all for responding. Now
for a new twist, one of our members has built a 'pay
out winch'. A pay out
winch is a drum with a break on it. The glider hooks
up about 200' behind
the tow vehicle, and as the glider climbs, the line
spools out. Does
anybody have any experience with this type of launch?
How much runway do
you need for this type of launch, how high can you
get, ect?

Boggs





  #53  
Old October 28th 03, 10:40 PM
Bill Daniels
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"Gary Boggs" wrote in message
...
I really appreciate all this good input, thank you all for responding.

Now
for a new twist, one of our members has built a "pay out winch". A pay

out
winch is a drum with a break on it. The glider hooks up about 200' behind
the tow vehicle, and as the glider climbs, the line spools out. Does
anybody have any experience with this type of launch? How much runway do
you need for this type of launch, how high can you get, ect?

Boggs


I've done lots of auto tows and winch launches but no payout winch launches.
But, I have done some back of the envelope calculating for payout winches.
Payout winches seem to work fine for hang gliders where the towing speeds
are far lower than sailplanes. The speeds needed for sailplanes really jack
up the numbers.

Assuming no wind, (Given enough wind, anything works - even a large stake.)
the tow car has to accelerate to the normal towing speed plus the payout
rate. The normal glider airspeed at the beginning of the climb will be
about 55 - 60 Knots. Correcting this for True Airspeed, depending on
density altitude, may be 70 - 75 MPH on the tow car speedometer. To pay out
enough wire to make the effort worthwhile, (Say, 2500 feet in 60 seconds)
the payout rate will be about 45FPS or 30MPH which brings the tow car speed
to 105MPH - a bit fast for my taste. Now the tow car speed will decrease as
the glider climbs so the distance required will be less than that covered at
100MPH for one minute. But you have to add in the distance to accelerate
and stop the tow car.

Juggle the numbers for yourself but it looks like you will need a 12,000
foot runway and really fast car - or lots of headwind. Consider also that a
heavy two-seater will demand nearly 250 HP at the tow hook and a wire
tension of about 1300 pounds. Your tow car had better be heavy as well as
fast.

This starts to make a standard winch launch look good.

Bill Daniels

  #54  
Old October 28th 03, 10:55 PM
Bob Mowry
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Beware of the raw statistics.

How about this one:

100% of 2003 US glider fatalities occur after aerotow.

Sounds like a good tag line for a winch manufacturer advertisement

-bob
  #55  
Old October 29th 03, 12:26 AM
Adrian Jansen
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I was lucky enough to get a kite launch one day. We had about 35 Kts of
wind on the ground, and someone suggested we try a launch. An instructor
and I climbed into a Blanick L13, launched ( *very* short run ! ) and
climbed to 4300 ft still on the wire. Of course we needed the expert
cooperation of the winch driver, who eased off the power as we got about 500
ft, then payed out cable to let us climb. At the end, it was mostly the
weight of cable ( single strand high tensile steel wire ) which determined
the max height, although there wasnt much wire left on the drum.

--
Regards,

Adrian Jansen
J & K MicroSystems
Microcomputer solutions for industrial control
"Stefan" wrote in message
...
Bob Johnson wrote:

Your ability to get 600 m releases with a winch on a 1200 m strip seems
extraordinary.


It all depends on the wind. With zero wind, the rule of thumb is that
you get approximately 1/3 the cable lengh. More with headwind, much more
with strong headwind. With extraordirarily strong headwind, you can even
kite. (Yes, it has been done.)

Stefan



  #56  
Old October 29th 03, 04:02 AM
Tim Ward
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"Gary Boggs" wrote in message
...
I really appreciate all this good input, thank you all for responding.

Now
for a new twist, one of our members has built a "pay out winch". A pay

out
winch is a drum with a break on it. The glider hooks up about 200' behind
the tow vehicle, and as the glider climbs, the line spools out. Does
anybody have any experience with this type of launch? How much runway do
you need for this type of launch, how high can you get, ect?

Boggs


I have quite a bit -- in hang gliders. It works best with lots of road,
runway, or dry lake.
We typically got about 2/3 of the paid-out line in altitude. With 6000 feet
of 3/16 inch polyprop, we could get 4000 feet.
More typically, we'd tow until we hit a thermal somewhere above 500 feet.

If you don't have a dry lake handy, you can "step tow". The tow car stops
at the end of the road, and turns around (either a U turn or a "Y" turn), as
the glider also turns around, being careful not to wrap the rope around the
wing.
When the glider is more-or-less turned around, the tow car starts again.
Rinse, lather, repeat. The downwind run takes much less time.
This might not work in sailplanes. In hang gliders, we were using a
three-ring release, which doesn't back-release.

Tim Ward


  #57  
Old October 29th 03, 04:02 AM
Eric Greenwell
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In article , mowry86
@hotmail.com says...
Beware of the raw statistics.


How about this one:

100% of 2003 US glider fatalities occur after aerotow.

Sounds like a good tag line for a winch manufacturer advertisement


Unfortunately, not true: some have occurred after self-launch, and I
know there have been some ground launch fatalities (how recently, I
can't remember)
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)
  #58  
Old October 29th 03, 04:16 AM
Bob Johnson
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Eggert --

Those are really good numbers for your winch.

With V8 300 HP (GMC 454 c.i., 7.4 L), and 5000 ft (1550 m) Plasma line
laid out, we are getting the rule of thumb 1/3 cable length releases of
1700 ft (525 m). This is into 10-15 kt wind. Much over that, we leave
the Blanik in the barn!

BJ
Midland, Texas







Eggert Ehmke wrote:

Bob Johnson wrote:

Mr. Ehmke --

Your ability to get 600 m releases with a winch on a 1200 m strip seems
extraordinary. Is your cable length just 1200 m also or is it greater
than your strip length?


That's 1200 m of cable laid out, with a V8 240 HP engine at the other end.
What I told is the normal range - with strong wind aligned to the runway we
had 750 m (2460 feet) agl with a double seated ASK21. I did not see this
launch, but it sounds reasonable. 650 m I have experienced myself.
Eggert

  #60  
Old October 29th 03, 06:08 AM
soarski
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Good Morning!

I Think Gary had a similar question or topic here, a year ago or
longer.
Seems to me, he likes winches, but his club has doubts.

I was trained with winch launches to solo in Germany, after I had
already learnt to fly airplanes in the US. Subsequently I got into
soaring in CO with aerotow, the going thing. Visiting Germany through
the years, I realize how much more experience there is about that
method. There are many places, where there is winch launch only! There
are pilots with two years experience of flying who have never seen an
aero tow!

One canot make any comparison or have statistics! It all depends who
does it, and his knowledge. When I look at modern winches and
everything that goes with it, winch launching is really quite
complicated and specialized.

Take a good Towplane, a good instructor, a talented pilot, and in no
time one has a towing operation going. In the US, to start a winch
operation, which is as perfect as Oerlinghausen or similar would take
a lot. To my knowledge, there is not a decent winch in the US, by
comparison to Germany and what they have.

Bill Daniels knows his stuff, but I think he is the exeption in the
US.

As for Gary Boggs, the only thing I can suggest is to go to Germany
for a summer and learn the trade. Winches, how to run them, including
the infrastructure. (Telephone)

On the other hand, with more reasonable selflaunchers coming out, the
winch effort may not be the answer anymore in the US. There are enough
reasons mentioned in this thread.

Happy Halloween
 




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