Let's talk ground launching........

On Sat, 03 Sep 2005 23:40:08 +0100, Robin Birch wrote:

We averaged 1,000 to 1,500 ft launches but did get to much higher on
occasion. (1 Mile Runway). We replaced the system with a Skylaunch winch
using stranded steel wire. This is much more repeatable and gets launches
between 1,400 and 1,800 feet with a much greater availability.

I was once winched in an SF-25 there. It was pretty calm
but we still made 1300 ft. The ride up was quite odd: climbing out
steeply with a stationary three-blader in front. We glided around for
400 feet before hitting the starter and flying back to Nympsfield.

--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Ian Johnston wrote:[snip]Who operates the guillotine in these systems?
Do you need someone stationed by the pulley, or is there some sort of
remote actuation? [snip]

The pulley was mounted on the back of a large, heavy truck, chocked to
stop the forces dragging it down the runway. The guillotine control was
a knob in the back of the cab (seat reversed on the passenger side IIRC)
which released the spring loaded chisel if required. We always had a
chopper person there during launching as a safety precaution, and they
had to be in the cab because of the danger of thrashing wire after a
break or chop.

They also served to speed up the launching process, by gathering the
drogue and strop etc. to hook onto the tow truck when it drove up.

For fastest turnaround, two tow trucks are used. One does the launch,
carries on to the launch point after glider release and delivers that
end to the next glider. The other follows the launched glider up the
runway, passes the launching truck half way, and arrives at the pulley
in time for the chopper person to hook on. The cable is double ended, of
course, with drogues and rings etc. at both ends. An extra ring on the
main cable goes to the tow truck Tost release, so no wear and tear on
the drogue etc. at that end when launching. At its best, it gives
similar turnaround to the Long Mynd's cable retrieve winch system - 20
or more launches per hour.

It is only worth doing all this if you need a lot of launches. Straight
autotow is quicker and cheaper to establish, needs less training and
manpower to operate, but is a bit harder to get a quick turnaround. You
can use two tow trucks to speed it up, if you have a wide runway - one
retrieves the cable it has launched with and returns to the launch
point, while the other does the next launch. Safety precautions need
some care with this - we did it in the 1970's when there were fewer
legal cases likely in the event of nasty incidents.

Chris N.






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There are other risks than the glider hook hanging up. At North Weald,
we broke a child's leg when the drogue dropped into a group of young
football players and dragged one of them along the ground - the chopper
man decided not to pull the release but should have done. (Agreed there
were others things that should have avoided such accidents, but Sod's
law says that if something can go wrong it will if you keep trying long
enough.)

The requirement for a guillotine should not be dismissed lightly.

We also had a fatal accident on the ground - one end of the cable
snagged during retrieve, got very tight, and snapped back when a man at
the launch point went to release it, pulling him over, resulting in a
fractured skull. Tow truck driver didn't know there was a problem. The
victim forgot his training, to ensure the cable was slack before
releasing it from the truck. (If the chopper man had cut it when it
snagged, it would not have hurt anyone.)

Launch systems can bite, and will, if safety is not taken very
seriously.

Chris N.




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At 09:36 03 September 2005, Ian Johnston wrote: (snip)
Personally, I think it's time we stopped messing about
with spring
loaded cutters and went to explosive ones, but that's
incidental here!

Ian

Er.......you are kidding, right?