Ground launching equipment question

Andy wrote:
On Oct 30, 12:42 pm, wrote:
On Oct 30, 1:49 am, "Bert Willing" bw_no_spam_ple...@tango- On this (aborted) launch, I was still rolling, both wheels on the
ground. I noted the chute opening in front of other gliders too,
while on the ground. I'd had no problems launching with our non-
chuted poly rope.

How springy is 3000 feet of spectra? I imagine that would be more of
a factor for auto tow than winch. I'm speculating that the problem
with the spectra launch is not the parachute itself but the dynamics
of the rope tension. The result may be strongly dependant on how the
tow vehicle accelerarates to nominal launch speed.

Andy

That makes senses. My guess would be that the tow vehicle changed gear
and thus briefly reduced power, which would probably be enough to allow
the chute to start to open. Some automatic gearboxes have quite a
deliberate gear change, enough to reduce the tension on the rope. If
there's a lot of spring in the rope a gear change could set up some
brief oscillation, enough to allow the chute to flap around.

Did it close again, or remain open? If the latter, either the tow
vehicle wasn't pulling or there's something very odd about the chute design.

On Oct 31, 3:40 am, Chris Reed wrote:
Andy wrote:
On Oct 30, 12:42 pm, wrote:
On Oct 30, 1:49 am, "Bert Willing" bw_no_spam_ple...@tango- On this (aborted) launch, I was still rolling, both wheels on the
ground. I noted the chute opening in front of other gliders too,
while on the ground. I'd had no problems launching with our non-
chuted poly rope.

How springy is 3000 feet of spectra? I imagine that would be more of
a factor for auto tow than winch. I'm speculating that the problem
with the spectra launch is not the parachute itself but the dynamics
of the rope tension. The result may be strongly dependant on how the
tow vehicle accelerarates to nominal launch speed.

Andy

That makes senses. My guess would be that the tow vehicle changed gear
and thus briefly reduced power, which would probably be enough to allow
the chute to start to open. Some automatic gearboxes have quite a
deliberate gear change, enough to reduce the tension on the rope. If
there's a lot of spring in the rope a gear change could set up some
brief oscillation, enough to allow the chute to flap around.

Did it close again, or remain open? If the latter, either the tow
vehicle wasn't pulling or there's something very odd about the chute design.

The chute stayed open. (at least until I was too sideways to see it!)

I would like to add some more facts to help determine the problem I am the
owner of the tow vehicle spectra line and chute. The chute is a toast
cross- panel and is 1450 mm diameter. It came with the minimum 2 m
connecting cable and 3 m safety cable. 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 The tow
vehicle has skid control on it witch means if the tires breaks traction the
computer automatically backs of power to get traction back. Since the first
day towing with it we have figured out how to disable it. I don't know for
positive if it was disabled during the tow in question because there was a
new driver at time. Unless the ignition was turned off then it should of
still been disabled. There was two more contributing factors 1 allot of the
dry lake bed was soft. The tow vehicle was breaking the crest and in some
places leaving 3 inch deep tracts. 2 the winds was variable and had a
slight till wind about half of the day. Some times the tow vehicle was
doing 65 to 75 all the way till some gliders was releasing. I think more
then pilot error or vehicle driver error I believe it was a combination of
several factors butt I would be interested in other thoughts.
John



wrote in message
ups.com...
On Oct 31, 3:40 am, Chris Reed wrote:
Andy wrote:
On Oct 30, 12:42 pm, wrote:
On Oct 30, 1:49 am, "Bert Willing" bw_no_spam_ple...@tango- On this
(aborted) launch, I was still rolling, both wheels on the
ground. I noted the chute opening in front of other gliders too,
while on the ground. I'd had no problems launching with our non-
chuted poly rope.

How springy is 3000 feet of spectra? I imagine that would be more of
a factor for auto tow than winch. I'm speculating that the problem
with the spectra launch is not the parachute itself but the dynamics
of the rope tension. The result may be strongly dependant on how the
tow vehicle accelerarates to nominal launch speed.

Andy

That makes senses. My guess would be that the tow vehicle changed gear
and thus briefly reduced power, which would probably be enough to allow
the chute to start to open. Some automatic gearboxes have quite a
deliberate gear change, enough to reduce the tension on the rope. If
there's a lot of spring in the rope a gear change could set up some
brief oscillation, enough to allow the chute to flap around.

Did it close again, or remain open? If the latter, either the tow
vehicle wasn't pulling or there's something very odd about the chute
design.

The chute stayed open. (at least until I was too sideways to see it!)

On Nov 2, 10:59 am, "John Cagle" wrote:
Some times the tow vehicle was
doing 65 to 75 all the way till some gliders was releasing.

I'm surprised that the tow vehicle was going that fast. Did the
gliders ever get into a normal ground launch climb attitude?

What vehicle speeds are other auto tow users seeing on calm wind days?

Andy

I owned a Speedastir. Aileron control was never great on takeoff. If a
wing goes down there was every chance it would stay there. Picking up
a wing with ailerons was a bad idea. Was more responsive to rudder.
If the wing hits the ground release immediately unless you are VERY
sure you can get it back up.
Cheers
Mark.

Cheers
Mark

On Nov 3, 5:36 am, Andy wrote:
On Nov 2, 10:59 am, "John Cagle" wrote:

Some times the tow vehicle was
doing 65 to 75 all the way till some gliders was releasing.

I'm surprised that the tow vehicle was going that fast. Did the
gliders ever get into a normal ground launch climb attitude?

What vehicle speeds are other auto tow users seeing on calm wind days?

Andy

If a wing drops to the point where you are sure it will hit the ground release
immediately. If you start a ground loop with a winch line attached the results
are very fast, and frequently result in a lot of damage to the glider and its
contents...

Fish wrote:
I owned a Speedastir. Aileron control was never great on takeoff. If a
wing goes down there was every chance it would stay there. Picking up
a wing with ailerons was a bad idea. Was more responsive to rudder.
If the wing hits the ground release immediately unless you are VERY
sure you can get it back up.
Cheers
Mark.

Cheers
Mark

On Nov 3, 5:36 am, Andy wrote:
On Nov 2, 10:59 am, "John Cagle" wrote:

Some times the tow vehicle was
doing 65 to 75 all the way till some gliders was releasing.
I'm surprised that the tow vehicle was going that fast. Did the
gliders ever get into a normal ground launch climb attitude?

What vehicle speeds are other auto tow users seeing on calm wind days?

Andy

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

Hi John

On Fri, 02 Nov 2007 10:59:32 -0700, John Cagle wrote:

I would like to add some more facts to help determine the problem I am the
owner of the tow vehicle spectra line and chute. The chute is a toast
cross- panel and is 1450 mm diameter. It came with the minimum 2 m
connecting cable and 3 m safety cable. 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 The tow
vehicle has skid control on it witch means if the tires breaks traction the
computer automatically backs of power to get traction back. Since the first
day towing with it we have figured out how to disable it. I don't know for
positive if it was disabled during the tow in question because there was a
new driver at time. Unless the ignition was turned off then it should of
still been disabled. There was two more contributing factors 1 allot of the
dry lake bed was soft. The tow vehicle was breaking the crest and in some
places leaving 3 inch deep tracts. 2 the winds was variable and had a
slight till wind about half of the day. Some times the tow vehicle was
doing 65 to 75 all the way till some gliders was releasing. I think more
then pilot error or vehicle driver error I believe it was a combination of
several factors butt I would be interested in other thoughts.
John

My experience is with winching, not auto tow, but a few things we have
learnt along the way. (We have also used a Tost cross panel chute, and a
number of similar designs.):

- The only thing that keeps the chute closed during launch is the cable
tension. This is determined by both the pilot and the winch driver. A
smooth constant acceleration on the part of the winch driver during the
ground run, followed by a smooth rotation into a steady climb on the part
of the pilot keeps the chute closed. Maybe your acceleration is just too
slow to keep enough tension to keep the chute closed. As a comment, we use
these chutes so that the winch driver can control the cable after release
and wind the cable to a point where the chute lands close to the runway.
With auto-tow your requirements may be different and a large chute may be
unnecessary.

- You must have a sufficient distance between the glider and the chute to
eliminate the possibility of the glider overrunning the chute and it
getting snagged in the glider. This could result in the glider being
launched for example, by the tail skid - which has resulted in fatal
accidents in the past. The Soaring Society of South Africa recommends 15m
to 25m between the rings and the chute (some other countries use a little
less but follow the same principle). The additional length also helps
prevent stones picked up by the chute during the ground run from hitting
the glider canopy and leading edge.

- You must stiffen the section of cable immediately in front of the release
rings with a hose pipe or similar. This is to prevent it from getting
picked up in the main wheel or similar resulting during an overrun. This
would result in the glider getting launched with no means of releasing the
cable - also a cause of fatal accidents in the past. The Souring Society of
South Africa recommend a minimum 15m length of stiffened cable (other
countries use a little less).

- You should have a means of releasing the cable from the tow car in case
of a hang up emergency as described above. The driver should also carry
a sharp knife, as a backup to cut the cable in the event of the release
mechanism failing to operate.

- The British Gliding Association recommends that a winch launch be
commenced with the pilots hand holding the release knob. If the wing
touches the ground the pilot should release immediately. If the wing tip
gets caught on the ground a "cart wheel" accident can occur very quickly,
often with serious injury or fatality.

Winching is conducted safely on a large scale in many parts of the
world. The above lessons have already been learnt the hard way and you do
not want to go through the same learning curve again!

Have fun.


Ian

On Nov 2, 10:36 am, Andy wrote:
On Nov 2, 10:59 am, "John Cagle" wrote:

Some times the tow vehicle was
doing 65 to 75 all the way till some gliders was releasing.

I'm surprised that the tow vehicle was going that fast. Did the
gliders ever get into a normal ground launch climb attitude?

What vehicle speeds are other auto tow users seeing on calm wind days?

Andy

The truck was accelerating to 60ish, then easing off the gas when the
glider achieved climbing attitude. I was consistantly climbing at 60
- 62 knots at close to 45 degrees. On the 1800' poly rope I got 1200'
altitude.