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