Ground launching equipment question

Last weekend our club did some ground launching from a nearby dry
lake. I had two very successful launches using our "cheap" 1800'
rope. With the cheap rope we don't use a parachute on the cable.
When I tried to launch with the 3000' spectra rope, equipped with a
parachute, the chute at least partially opened when the glider was
going around 40 knots, and depsite full right rudder, the glider
ground looped to the left. All the pictures I've ever seen
(admittedly very few) of the cable chute used for winch or vehicle
tows seem to show the chute' is completely 'closed' when the rope is
still attached to the glider. I'm sure pilot error had a part in this,
but it really seemed that when the chute opened, I lost what little
rudder authority I had. It also occurred to me that the
Speed Astir verticle stab and rudder is one of the shortest
(vertically) around, and that may have been a contributing factor.
The dust cloud was quite impressive!
Jim

What's the distance between the crown of the parachute and the
attachment to the glider? Should be at least 30 feet.


Dan

On Oct 29, 10:10 am, Dan G wrote:
What's the distance between the crown of the parachute and the
attachment to the glider? Should be at least 30 feet.

Dan

Seemed more like 10 or 15, but certainly less than 30.

wrote:

What's the distance between the crown of the parachute and the
attachment to the glider? Should be at least 30 feet.

Seemed more like 10 or 15, but certainly less than 30.

I winch launch a lot, but have never seen 30. 10 to 15 seems reasonable
to me.

On Oct 29, 7:07 pm, John Smith wrote:
I winch launch a lot, but have never seen 30. 10 to 15 seems reasonable
to me.

That's the general recommendation from Tost (or rather, 10m is). We
used to use less but now use the correct length - it's a lot more
comfortable.


Dan

On Oct 29, 3:30 pm, Dan G wrote:
On Oct 29, 7:07 pm, John Smith wrote:

I winch launch a lot, but have never seen 30. 10 to 15 seems reasonable
to me.

That's the general recommendation from Tost (or rather, 10m is). We
used to use less but now use the correct length - it's a lot more
comfortable.

Dan

Shouldn't the 'chute stay closed though? I'm sure I wasn't clear, but
that was the root of my question.

At 18:01 02 November 2007, John Cagle wrote:
The chute kept fully opening the
first day I used it. You can see it in the video that
I have on my web
site. http://www.caglesonline.com/video/autotows.wmv
Since that day I have
increased the 2 m connecting cable to 4 m. It does
a better job as you can
see in the next video taking the same day and place
that jims glider ground
looped. http://www.caglesonline.com/video/07fallroachlake.wmv

It looks from the videos as if the towing cable is
split in four and looped over the chute so it is trying
to keep it closed only because of the tension in the
cable. I think the chute is almost bound to open with
this arrangement. In all the ground launch cables I
have seen and used - for both winch and auto tow -
the strop attached to the glider goes directly to the
apex of the parachute so that the chute itself is part
of the cable and is kept closed by its own tension.

And 65 or 70 mph seems far too fast. At any reasonable
launch angle the glider airspeed is considerably more
than the tow car speed so for a good launch at say
55 or 60 kt into a light wind, the car should be doing
no more than 30 or 40 mph.

Neil

I agree about the chute.

All the winch launching parachutes I've seen (and the principle should
be the same) are constructed roughly as follows:

1. Take four squares of material (lozenges might be better, and possibly
some curvature in some of the sides - you'd need to experiment).

2. Attach one corner of each to the other four to form the apex of the
chute. The cable to the glider goes to this apex.

3. Sew the squares together along (for each) the two sides which meet at
the apex (think jellyfish?)

4. Connect the four free corners by tapes or ropes about 3 or 4 feet
long to the cable connected to the tow car. Most chutes I've seen have a
heavy duty tape stiched from the apex of each square to the free corner,
then continuing to form the junction to the tow car cable.

Chutes like this stay closed so long as the cable is under more than
minimal tension.

You'd need to experiment - maybe start with four handkerchiefs and some
pins to see if my description translates into something usable?


Neil MacLean wrote:
At 18:01 02 November 2007, John Cagle wrote:
The chute kept fully opening the
first day I used it. You can see it in the video that
I have on my web
site. http://www.caglesonline.com/video/autotows.wmv
Since that day I have
increased the 2 m connecting cable to 4 m. It does
a better job as you can
see in the next video taking the same day and place
that jims glider ground
looped. http://www.caglesonline.com/video/07fallroachlake.wmv

It looks from the videos as if the towing cable is
split in four and looped over the chute so it is trying
to keep it closed only because of the tension in the
cable. I think the chute is almost bound to open with
this arrangement. In all the ground launch cables I
have seen and used - for both winch and auto tow -
the strop attached to the glider goes directly to the
apex of the parachute so that the chute itself is part
of the cable and is kept closed by its own tension.

And 65 or 70 mph seems far too fast. At any reasonable
launch angle the glider airspeed is considerably more
than the tow car speed so for a good launch at say
55 or 60 kt into a light wind, the car should be doing
no more than 30 or 40 mph.

Neil

Jim,
My experience is with winch launching. Have done it for many years in
Europe.
By looking at the video, the climb angle is way too shallow, at least
of it were a winch launch. The chute opens while following the rope
after initial lift off.

Following the rope is never a good idea unless you're going to
release. At least with winches.

Right after lift off, one should start climbing gradually and increase
the angle once more than 100ft. That way the rope tension stays firm.

If the air speed should become uncomfortably slow or remain too slow,
you can release safely at 100ft or more. Height = safety - even when
slow. So you always want to get some air under the wings and keep the
rope tension up.

By pushing the nose over even at low airspeeds and then releasing, you
won't stall and land straight ahead and see why the speed was too low.

But following the rope on initial launch for more than 2-3 seconds
because the speed isn't high enough, is not proper technique, at least
not on the winch and I would say probably on a car tow as well.

Either release immediately and abort or gently climb out for the first
100ft and then release if speed remain too low for comfort.

Ground launch requires very quick reaction without any hesitation.
There for it requires a plan of action firmly in place ahead of time
that needs to be followed during launch. If the pilot is prepared
properly and knows how to react given the situation, I think it is
much safer than aero tow.

Once you're over 100ft, nothing much can go wrong.
Tom

Even on the second video, the pilot is heard saying "almost level
attitude" on initial climb out. That is totally wrong technique and
the chute is opening in front of him as a result. That as we saw, is
dangerous.

He would need to climb out a little steeper for the first 100ft and
all would be OK.

Even on winches the chute can open for split second sometimes, but as
the pilot pulls, they close back up again.

Also the climb in the second video is not done very smooth. Proper
technique is to gradually start easing back on the stick and leveling
off as maximum altitude is reached. You will know this because the
sailplane will start rocking back and forth, pitching the nose up and
down, if you don't ease back and the angle remains too steep. The
plane does not like to be dragged through the air at a high angle of
attack, which is what happens when the angle is too steep - regardless
of the airspeed.

Suddenly leveling out and releasing means the maximum altitude was not
reached. Either they leveled off too soon or too late.

Then again, maybe the car had to stop due to a limited ground run.
Then the release technique used in the second video is understandable.
Otherwise not.