Safety of winch launch vrs. aero tow?

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".

Haven't heard about that, but I _have_ heard about a hairy thing called
"step towing", which is something the hang-glider pilots do from small
fields. They winch up to say 150m, have the winch pay out as the fly
back, turn and take another winch launch from altitude! This can of
course be repeated for as many times as practical, and some respectable
altitudes can be gained.

Imagine this done with a glider and dyneema or spectra cord for wire.
You would of course have to modify the tow-hook to not automatically
back-release (shudder, gulp!)...

Well, if someone actually tries this with a sailplane I'm not sure I'd
want to know. They would certainly not be allowed to fly _my_ glider
anyway.

Christian 8-)

The HG community used (has used) pay-out winches for a number of years. At
least one major auto maker produced a limited production launch vehicle
pick-up truck as advertised on national TV. Others were retro-fits or home
grown. The current generation of US UL gliders, Sparrowhawk and Lighthawk,
could probably use these as supplied. The Apis and Silent might need
something a bit more stout.

Frank Whiteley


"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

"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

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

In article , "Adrian Jansen"
writes:

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.

Yessss, but!!

I suggest you now estimate the wing loading with 4300 ft of high tensile steel
plus the down pull of the winch. Because you cannot feel the "G" loading on a
winch does not mean it is not there and two effects occur.

1) Your stalling speed increases with the weight of cable dangling below you,
and,

2) the G loading increases by the weight of cable attached to your glider so
you MAY be far exceding your all up "weight".

Beware, whilst this may be great fun, you get much closer to the envelope
limits than you know.Care is needed.

Barney
UK

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

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

Bob Johnson wrote:

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


1/3 cable length seems low. There was in France an experiment showing
40% cable length without wind with cable length from 1000 to 2000 m.
See HTTP://www.gliderforum.com/thread-vi...geID=1466#1466

"Bob Johnson" wrote in message
...
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

Bob, When winching, the wind is your friend. Quitting at 15 knots is not
necessary. I have winched into 35 knots and higher winds and the results
are spectacular. Each 10 knots of headwind is the equivalent of about 40
additional HP.

The thing that often severely limits the altitude gained is a slow pitch-up
profile at the start of the launch. The final height achieved is largely
determined by the profile flown in the first few seconds of the launch.

Now, as everyone has pointed out, you need to be careful here. Safety at
the start of the climb is a combination of airspeed, altitude and attitude.
The more you have of the first, the faster you can get the second two and
the higher you will get.

I've done calculations, simulator runs (X-Plane) and flight test to prove
the following point. If you have 60 knots in a glider with a stalling
airspeed of 40 knots, you can be in full climb attitude at zero altitude and
still have a large safety margin. Practice this way - at several thousand
feet AGL, zoom the glider into a 50 degree nose-up attitude. As the
airspeed decays to 60 knots, yell "WIRE BREAK", delay 0.5 seconds
(simulating reaction time) and pitch forward at zero G. Watch the airspeed
and altitude, you'll see what I mean. (For winch CFI-G's, this is a great
way to teach how to handle wire breaks.)

If you have (or simulate) a wire break at this point and start a zero G
pitch over after a .5 second delay, the minimum airspeed during the
parabolic ballistic trajectory will be about 50 - 55 knots when the glider
reaches apogee at an altitude of about 100 feet AGL. So there you are at
100 feet and 55 knots in a normal gliding attitude - not exactly a
problematic situation, just land straight ahead. The reason this works is
that the glider's induced drag at zero G is minimal so the airspeed decay is
mainly just due to gravity and the glider follows a parabolic trajectory
until the pilot re-establishes one G at the normal glide attitude.

I need to repeat that I am not advocating a rocket blast-off kind of climb
profile but a smooth transition into the full climb without undue delay
equipped with a full understanding of the safety margins.

Bill Daniels

JJ -

I, as a power pilot, learned to fly sailplanes on the winch, overseas. I
now only fly aerotow, and am not signed off for ground launch. One thing I
have not seen mentioned is the qualification of winch operators. Tow plane
pilots ( I'm not one) have to meet certain standards and be signed off. I
became a winch operator by volunteering out of club spirit (stupidty?). I
was informally instructed by a winch operator who desparately wanted to
escape the exile of the winch. Then I was left to do the job, getting my
flights at the end of the day. They brought me food and drink
(nonalcholic), but no one "qualified" on the winch would come near for
hours. I'm sure I never endangered any aircraft or pilot, but I'm also sure
that some achieved less than optimal release altitude. There was no
tensionmeter, and throttle control was based on visual evaluation of
aircraft attitude and cable sag.

Many years later I had the chance to observe the operator of a modern
six-reel winch at Terlet. He was an artist at work, and he had the best
equipment.

I think winch launches are safe, as long as you have a cg hook. But, in any
comparison to aerotow, the increased number of launches necessary to achieve
sustained flight must be taken into account.

Ed Grens

"E. A. Grens" wrote in message
...
JJ -

I, as a power pilot, learned to fly sailplanes on the winch, overseas. I
now only fly aerotow, and am not signed off for ground launch. One thing
I
have not seen mentioned is the qualification of winch operators. Tow
plane
pilots ( I'm not one) have to meet certain standards and be signed off. I
became a winch operator by volunteering out of club spirit (stupidty?). I
was informally instructed by a winch operator who desparately wanted to
escape the exile of the winch. Then I was left to do the job, getting my
flights at the end of the day. They brought me food and drink
(nonalcholic), but no one "qualified" on the winch would come near for
hours. I'm sure I never endangered any aircraft or pilot, but I'm also
sure
that some achieved less than optimal release altitude. There was no
tensionmeter, and throttle control was based on visual evaluation of
aircraft attitude and cable sag.

Many years later I had the chance to observe the operator of a modern
six-reel winch at Terlet. He was an artist at work, and he had the best
equipment.

I think winch launches are safe, as long as you have a cg hook. But, in
any
comparison to aerotow, the increased number of launches necessary to
achieve
sustained flight must be taken into account.

Ed Grens

If it's soarable, one launch should do most days. Most seasons I winch
launched regularly I can count on one hand the number second snaps taken per
season to soar away. Of course, _big wings_ do help, but that's another
thread;^) This season, I only took two aerotows to 2000agl. My other AT
releases were 1200 to 1700agl, that is, at or below winch height and near
enough to the airfield to presume had we been winching, getting away was
pretty likely. For a number of reasons we didn't winch much this season,
but when we did, we soared. This included thermals on New Year's Day and
wave on Feb 1 and thermals each subsequent winch day this season. Looks
like snow for November 1st though. Last Saturday would have been perfect as
lift was 10kts to 12K in a stiff NW breeze. The kind of day we get 2500+agl
on the wire.

Frank Whiteley