Parks College Parachute Research Group
Using a flexible cable closing pin on an experienced skydiver's rig
Investigator: Gary Peek
Purpose of this study
To determine if a flexible cable closing pin is a practical method of
closing the containers of rigs for experienced skydivers.
Background
1. My personal rig, a North American Aerodynamics Centaurus, contains a
canopy smaller than it was designed for, and tension on the closing loop when
the container was closed is very light even with the shortest loop length
possible. (The loop originates at the bottom flap, the first one in the
closing sequence, not on a tab between the reserve and main, which would allow
for more adjustment.) I was concerned about the security of the curved steel
closing pin and had considered ways to increase the security of the pin.
2. A skydiver had mentioned this topic on an Internet newsgroup and had
posed the question (to all) as to why harness/container manufacturers did
not offer flexible cable closing pins on rigs for experienced skydivers,
since this could potentially provide a more secure method of closing rigs.
I responded personally to him that I thought the reason might be that the
wear to the closing loop would be excessive and that skydivers sometimes
do not replace their closing loops as often as they should as it is.
An Experiment:
I constructed an eight inch flexible cable closing pin from standard yellow
LOLON coated cable, which is the cable often used for cutaway handle cables
in skydiving rigs, and installed it on the bridle of
my Centaurus. This application produced a much more secure closing
of the container due to the distance that the cable would need to be moved
in order to cause the container to be accidently opened. Deployments were not
noticably different from using a curved steel closing pin.
The closing loop used was made from Type IIA suspension line sheathing,
a typical closing loop type used on experienced skydiver rigs, and has a
strength of approximately 100 pounds. The pilot chute used on this rig is a
34 inch zero porosity collapsible type.
Important installation note:
Since a flexible cable pin of any length must move a great deal further than
a curved steel closing pin in order for the container to open, it was
imperative that I insure adequate bridle length between the closing cable and
the top of the deployment bag, otherwise, a container lock could occur.
Supporting Research:
I contacted Strong Enterprises, who has used flexible cable closing pins
on their Dual Hawk Tandem containers and who might have some information
on this type of closing pin. Ted Strong told me that the company originally
used a 400 pound "sheathing" type loop on Dual Hawk Tandem rigs but had
switched to an 1800 pound spectra loop, and that closing loops were lasting
much longer since then. He also stated that it was his experience that the
flexible cable they were using, (which is the type often used for closing
static line containers) is less likely to dent or distort than LOLON coated
"cutaway" cable for two reasons. First, the inner steel cable is a larger
diameter to begin with, and secondly, the clear plastic coating on that
cable is harder. He also mentioned that the force exerted during pin
extraction by a fully inflated drouge parachute used on a Strong Dual Hawk
Tandem rig was something that was never in doubt.
Conclusions:
I observed that a flexible cable closing pin creates considerably more wear
to a Type IIA suspension line sheathing type closing loop compared
to a curved steel closing pin. In as few as 10 jumps a closing loop of this
type shows wear that most skydivers would feel uncomfortable with, and
consider replacing the loop.
The combination of a flexible cable closing pin of sufficient hardness
and installed at an appropriate place on the bridle, a closing loop with
adequate strength and durability, and a pilot chute with adequate and
consistant drag could be a practical system of providing a more securely
closed rig than using a curved steel closing pin.
However, as in many mechanical systems, it is easy to overlook the critical
relationship between the components used in the system, and changing any one
component could have consequences beyond the end user's knowledge of the
system.
Update 5/99
At the PIA Symposium '99 I was given several 1800 pound spectra loops by
Strong Enterprises for use with their Dual Hawk Tandem rigs. I installed
one of these loops on my personal rig configured with a LOLON flexible cable
closing pin. Since that time I have made over 20 jumps in that configuration
with no noticable wear on the closing loop.
Update 10/04
I now have so many jumps on this configuration that I have lost count. Perhaps
500? I have replaced the loop about 7-8 times if I recall correctly, usually
with 1800 pound Spectra. About a year ago I noticed a small amount of wear on
one of the closing flaps where the cable attachment point rubs past the flap during
container opening, so I enclosed the cable's metal swage with binding
tape so that the swage could not come in contact with the flap. Since then
I have noticed very little additional wear.
Notice/Disclaimer: This study is not intended to suggest that a
flexible cable as a closing pin on an experienced jumper's rig is the
solution to any particular container problem, but is intended only to
provide information which we believe to be interesting and informative
to the skydiving community. If you have questions regarding a particular
harness/container system and its method of closing, always begin by
contacting the manufacturer.
For questions or comments about this study contact Gary Peek at
peek@pcprg.com
