Mayf;
I'd like to say that Nolan White's tragic accident was certainly one that
has deeply saddened the racing community as well as his immediate family.
Perhaps there is something that can be learned from it that may prevent
something similar from happening in the future. Parachute deployment on fast
LSR streamliners has been a problem area that could benefit from further
investigation.
However, I think there may be something missing in that link. I had to sneak
up on your parachute page by going to your home page first and going the
Analyses route.
Your analysis is certainly interesting and I can't offer much in the way of
data to the discussion but here are a few thoughts.
I have had considerable experience in caving and some in mountain climbing.
Both sports participants' lives depend on characteristics of their climbing
rope. The need for a rope of sufficient strength is obvious but within the
last 40 years or so another equally important characteristic has been
recognized-- elongation and energy absorption.
A climber on a difficult pitch is always "on belay", or securely tied with a
climbing rope from his nylon harness to a piton (for example) or to another
solidly- positioned climber who is holding the rope around his waist. Free-
climbers don't use rope belays; they are crazy. It is necessary to allow
some slack in the rope so the climber can move from one position to another
but this is minimized. If the climber falls, his body accelerates downward,
building up kinetic energy, until the rope is finally pulled taut. What
happens next is critical.
If the rope is Manila, like in the "olden days", the climber's body is
brought to a sudden stop, generating tremendous "G" loads. Even though he
has been saved from falling further, the stop may prove fatal. In actuality,
one or two pitons may be pulled out, slowing the sudden stop. Techniques for
belaying climbers were developed to slow the rate of deceleration by letting
the rope slide around a belayer's back and bring it to a slow stop. These
were difficult to do and were simply "work-arounds" for the basic problem:
Manila rope wouldn't stretch. Dacron and some other synthetics are also in
this category.
The development of nylon rope changed the whole character of climbing &
caving. Nylon stretches as it is pulled taut. This spreads out the time over
which the body is brought to a stop, greatly lowering the "G" forces on the
body and, consequently, the peak tensile load on the rope. Ordinary nylon
stretches but it also rebounds quite a bit. This is annoying but not
particularly dangerous; I've oscillated up and down 20 ft on a free drop
into a 180 ft cave (Hellhole- Pendleton Co. WV). Special climbing- grade
nylon rope has been developed to feature an excellent combination of tensile
strength, elongation, and energy absorption. These ropes absorb energy as
they stretch, minimizing injury to the climber and this also reduces
rebound.
Parachute tether line seems to have similar requirements to climbing rope--
it needs to stretch and absorb energy. The longer the tether, the more the
stretch and the lower the "G" forces and tensile loads. It may also be
possible to pay out the line dynamically to absorb lots more energy--
perhaps unwinding the tether line from something like a drum that has a
brake. The additional drag of the brake as the tether line pulled off the
drum might be one approach to reducing the "Yank" force on a parachute that
is deployed at high speed.
One thing I might mention-- probably highly controversial-- is the practice
of publishing details of accident investigations by the caving & climbing
communities. The National Speleological Society publishes "American Caving
Accidents" giving detail such as this:
http://www.caves.org/committee/er-ncrc/08287701.HTM and the American Alpine
Society publishes a similar report "Accidents In North American
Mountaineering" so that similar accidents can be avoided.
I wonder if something similar would benefit the racing community. Any
thoughts?
Regards, Neil Tucson, AZ
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